Is Gradual Variac Warm-Up Effective with Tube-Rectified Amplifiers ?

[@donaldthompson4857]

what is so great about these videos, is that you can watch them as many times as needed for the information to sink in , your a great teacher

[@UncleDoug]

Thanks so much, Donald. Rusty and I really appreciate your kind words....and we're glad you enjoy our videos :) ^. .^

[@bluesman97]

Nine Years later I get this video and it's still more informative than most. Uncle Doug Your a Gem.

[@UncleDoug]

We're glad it was clear and helpful, B97 :)

[@cassvirgillo3395]

Hey Uncle Doug, 'Ol Rusty, I sure miss him, what a sweet heart, he had a good life living with your family. Thank you so much for sharing your vast wealth of knowledge. I know Richard "Rick" McWhorter over at All American Five Radio, on YT, would like the Simpson 260 meter, me too. I like analog for the visual aspect of seeing what's going on, motor boating for instance. I hope all is good with you and yours, All the Best, C.

[@UncleDoug]

Thanks, Cass. Things have never been better :) To me, the best possible use of analog meters is in evaluating potentiometers......you can readily see (or not see) the smooth sweep that is impossible to monitor with a DMM.

[@gerardoromano3436]

What a great demonstration, Uncle Doug you were the best Nine years before, and you keep improving to this day, love you and your Channel.

[@UncleDoug]

Thanks so much for your very nice comments, Gerardo. We really appreciate them :)

[@stevenstewart5980]

Thanks, Uncle Doug for another great video! As you can see, I often go back into the treasure trove of your earlier videos. I love the videos you make of exploring, repairing and building amplifiers. But I especially appreciate the videos that you make showing how to be safe with your person and your equipment. These, I think, are your most important contributions to those of us who understand less about the whys and wherefores of certain procedures and having and using certain equipment like variacs, current limiters, etc. Thanks again for all that you do to help us safely enjoy working on high voltage electronics (personal safety and protecting our devices).

[@UncleDoug]

Thanks for acknowledging our efforts, Steven. Jack and I really care about our viewers and want you all to safely participate in our great hobby.

[@StuderRevox]

Just to say that I find your videos on vintage amps very educational and gives us a chance to understand better what is happening with such circuits. Please keep them coming and would be great to see videos in the future perhaps of explaining a full circuit of say a hifi vintage tube amp and helping us understand what each component is serving its purpose for. Many thanks :))

[@UncleDoug]

You're quite welcome, SR. It's good to hear that the videos are helpful. I believe I have posted videos that cover virtually every aspect of tube amplification, so please check out my channel menu. Thanks for watching :)

[@rsdmag]

I've been learning so much from your videos, thank you so much for making them! I'm always looking forward to the next 'Uncle Doug' video. They always inspire me to dig more deeply into my own equipment, and to see what I can make myself.

[@UncleDoug]

You're quite welcome, Dan. It's great to hear that the videos are helpful. Best of luck with all your projects :)

[@bretfuzz925]

I usually use an octal solid state diode (I make) and bring up the supply slowly with that. I will typically use that with a variac to slowly build the capacitors. Sometimes I will even use a resistor between the output of the rectifier and the rest of the circuitry to limit the current to something modest. I do love videos like this. Very informative. Thanks for posting.

[@UncleDoug]

I'm glad you enjoy our videos, Bret.

[@huberttremaine8343]

Wow the old Simpson 260! I still have mine. Just goes to show even a novice (not you) should have at least 2 VOMs. All juice caps(I call them that because electrolytic is too long of a word) all need the same treatment although the the working volts in a solid state circuit is usually much lower than tube, old filter caps need to be brought up slowly. Great as per-usual Doug. Rusty might have other things on his mind. Thanks

[@UncleDoug]

Thanks, HT. I rescued the old Simpson meter from a local pawn shop, where it had been languishing for months.....a filthy mess with battery corrosion and God only knows what else slathered all over it. Like all fine equipment, however, it cleaned up beautifully and now looks and operates like new. Glad you liked it :)

[@n4120p]

Using a variac not only slowly ramp up the voltage but also protects against the inrush current in the transformer and giving filaments a soft temperature ramp when they are cold , avoiding unnecessary damage ,,, variac , yes always a good reassurance

[@UncleDoug]

Are you advocating the use of a Variac every time that a tube circuit is turned on ??

[@n4120p]

@@UncleDoug yes .

[@highpath4776]

Dont forget it is probably the case in the UK where the input voltage is 250v AC RMS, can be noisy or you might just plug in at the peak +/- which for both tube, (capacitor) or transistor (probably more sensitive) circuits the use of a variac - which is also hopefully acting as an isolation transformer, there are benefits even though the primary and windings of a 240v transformer should still supply the normal design voltage to the rest of the circuit. A variac is an additional protection , particulary with old radios that have the joys of live dc return chassis (DO NOT PLUG A GRAM OR GUITAR ETC input into one of those !), and the fun world of selenium rectifiers. Additionally should you plug any input voltage into a circuit you have not visually checked or component tested if it is a item new to you, and the average home person digging out dads old equipment - or their own from younger days is just going to power up from the mains anyway. Indeed from your RMS measurements consider the peak voltage is going to rise proportionally differently to your RMS derived measured AC.

[@UncleDoug]

Thanks for your input, HP.

[@djfrank59]

Good morning Uncle Doug! Another great video of 'fact'. When I get older tube Amplifiers, Radios & other tube gear in for repair, I swear by my Variac. I've learned to use one religiously when I'm uncertain of an amps condition or how long it was hanging around before the last power-up. Although, I do open up the amp and give a visual inspection under the chassis before any AC gets put into it. However, as we both know, components that look good aren't always as they appear...especially electrolytic caps. From many years of experience, I've learned that this practice of slow voltage ramping is also a safety step. For a good amount of years, I've done what David B has done (I can relate) plug it in and see if anything or what blows up & smokes. After having one amplifier's power transformer go up in flames on my bench and my cat making a B-line for the top of my storage cabinet, I took my Variac (which was laying in the original sealed carton for 5 years) out of the box and placed it in it's permanent place on my workbench. David B also has a true point in his comment on this procedure for solid state amps...BJT's do need all the voltages correct at the same time. What I usually do is, when I get a solid state amplifier of uncertainty in for repair, this is where I use the incandescent lamp current limiter. At that point, I just need to know if there's a dead short or not. It saves trips to the breaker panel, or saves on wasting an extra fuse or two...not to mention possible added damage to the equipment. Another great video as always. This one's going to be in this week's home work lesson for the 3 private students I have :) Always great to see another video from you ::)

[@djfrank59]

PS: Looks like it was Rusty's day off :) One other procedure that I use and forgot to mention is, when I get a piece of gear that's been laying around, I also take resistance measurements on the transformer windings to make sure there are no shorted turns in either the primary or secondary taps; then I pull the rectifier tube and measure the AC voltages at the rectifier socket.

[@tubical71]

As for the "solid state" Amps is use my variac as well. Since i´m dealing mostly with "classic" PA-Amps and there are dual symetric voltage driven anyway. On some germanium (AC something transistors) Amps i prefer an AC current control device (I use a old german "elabo - netznachbildung" with AC current sense, limit and control ability) But, as you know, to limit the currrent you need to lower the voltage, so the voltage initially ramps up until the current is limited and it drops down or stays there but this depends on how you limit the current. With an in series resistor (= light bulb) you just limit the inrush current a little and/or add some dynamic(=ligh bulb) resistance to it, it works well, but the inrush current may do some harm.... Some Mains NTC resistors are great helpers here as well, since they act the opposite direction compared to a light bulb. They limit the inrush current and when they are heating up the resistance goes down and the "DUT" (=DeviceUnderTest) come to fully operation within 1-3 seconds. Some sort of "Automatic Variac" but sadly they don´t come cheap. Even the raw component itself is around 10 bucks and you´ll need minium two of them. And everyting around you´ll need to build up yourself and it must be save as it deals with mains voltage...

[@djfrank59]

I also use NTC resistors for testing purposes It's worth the build...Unfortunately, I have a Peavey CS-800 solid state amp on my bench right now where 5 output transistors are shorted, but a section of the PCB is charred beyond repair due to the customer wrapping the fuse with tin foil...

[@tubical71]

Do not remember me on that tin foil thing.....i hate people doin´that!! How many Amps came across my bench with that?? how many...?? some had been so beautiful until i saw this done to the fuse(s)...always beond repair....WTF?!?!

[@djfrank59]

I know, some people shouldn't own amplifiers (LOL) :)

[@johngeddes7894]

Some may have commented that Rusty was too brash, or bombastic - even demanding like many perfectionists tend to be. I find this NOT to be the case at all. We can see his careful tempo, sprinklings of insights, and often a perusal of the dreaded schematic! I would describe Rusty to be the consummate teacher in most respects! Thank you, Uncle Doug (and Rusty, wherever he may now be) .

[@UncleDoug]

Your analysis seems quite accurate to me. Many viewers assume that the "video" Rusty is an accurate portrayal, but in reality it is simply a very skillful act performed by a master thespian.

[@bryanmcwhirter9945]

Just came across this vid. and wanted to mention, as you have shown, should always have meters hooked up during any questionable operation. My variac is permanently on an ammeter and voltage output meter, no second guessing, don't like surprises or loosing my gear. Thankyou Uncle D!

[@UncleDoug]

You're welcome, Bryan. You make a valid point, and no one should ever forget to use a Current Limiter during repairs and analysis.

[@_David_E_]

Another great video Uncle Doug! I've always wondered if there was any point in doing this, so it's great to see this test. Thanks.

[@UncleDoug]

You're welcome, David. Although this procedure can't save electrolytic capacitors that have completely failed, it does enable reasonably functional components to gently return to functionality. Translation: It's not magic, but it generally works :)

[@_David_E_]

Uncle Doug Out of interest, would this procedure work just as well with solid state rectifiers?

[@UncleDoug]

Yes, David. The Variac slow start up has always been accepted/recommended for SS rectification. The only question was whether it would work with tube rectification also.....which is what the video investigated. With SS rectification, the DC output should begin immediately upon input of AC and should rise in direct proportion to the AC input.

[@UncleDoug]

Carl, for some reason your question had no reply capability. They probably recommended the solid state rectifier because they were under the impression that a tube rectifier does not put out DC at low input voltages; however, as shown in the video, it actually does. Either way, tube or diode, will work fine.

[@babybearkill1]

That's about right for a filament valve although i suspect the 6u4 will have quite a bit of hysteresis in hot to cold emission. Off to the Bat Cave to find out!

[@UncleDoug]

I believe the 6U4 is a half-wave rectifier, BB, and have never encountered one in a guitar amp. My experimentation was focused only on commonly used full-wave rectifiers, such as the 5U4, 5Y3, GZ34, etc. Let us know what you discover.

[@babybearkill1]

Will do. Secondly I need to ship the old tubes to you for restoration work. We have for you, 6v6, 5y3gt in the old bottle style. 6aq5, 12au7, EL33 yes, that's right plus a whole bunch of them made from the late 30s until the 70s. For my service work I can't really use them which is a real shame

[@babybearkill1]

And my bad, it was a typo

[@SuperJetjockey]

Thanks, I have seen both sides of this argued by "experts" , and just plugging it in has never worked for me. I am happy to see that you put a logical experiment together that makes a reasonable argument why it is worth the time to bring the voltage up slowly. Another use for my Variac, Thanks

[@UncleDoug]

You're welcome, SJ. I think virtually anything is better than simply plugging a vintage electronic device into a wall socket, turning it on, and hoping for the best. I always protect the circuit with a Current Limiter (video posted) and use a Variac for circuits that have been sitting for an undetermined (generally very long) period. Here's a simple test to prove that this "gentle" method works: Measure the ESR values in the filter caps of a dormant amp prior to slow start, and then after (gently discharge them first, of course).....the values will generally show a significant decrease. Any that don't should be considered suspect.

[@Ireland831]

LOL...I have that exact Simpson 260 multimeter (my dad gifted it to me 20 years ago). I now have a Radio Shack hand held along with a Fluke 87V. I wish I had found your videos years ago...I found out two things the hard way....the first was the voltage has to get turned up quite high before the tube rectifier output. I was watching TV as I was bringing up a new amp build. Every 10min I turned up 10v. When I got to around 60v or so I smelled something burning and zap....killed the PT. Now I start new builds with tube rectifiers with a rectifier plug. I also incorporated a dim bulb limiter, (which recently saved me on a new build with mis-wired SS rectifier). One last item....I recently picked up a Anatek Blue cap tester. I see that it can test caps 1uf and above. What do you do with the smaller caps??

[@UncleDoug]

The Anatek meter is strictly for electrolytic capacitors, Ireland. Non-polar caps can be tested with a capacitance meter and in circuit with one lead removed from the circuit (see my videos for details).

[@tubical71]

Great Video, Doug. This shows exactly what i´m saying everytime someone is asking me how to deal with old amps, a slow voltage rise is by far the best thing you can do when you check out some vintage electronics in unknown condition. Even better when performed in cunjunction with preheated tubes (if the amp has a standby switch).

[@UncleDoug]

Thanks so much, TC. We need to protect these poor old vintage devices.....especially now that I'm one myself :)

[@jonault2140]

i still do not know why i find all this so interesting! but thanks.

[@whynotme5926]

Good video-I've got to get me a variac before I start my first build but I am looking on ebay trying to find one cheap, but haven't had any luck yet.I'm going to have more money in testing equipment and such, than the amp!!! Thanks.

[@UncleDoug]

You can live without a Variac, WN, but you can't live without a Current Limiter. See my video on how to build one.

[@ianbanhamamprepair9457]

Another great video Uncle Doug. Your Simpson meter reminded me of the big old bakelite Avometers we used to use in the R.A.F. years ago [ quality equipment ].

[@UncleDoug]

Greetings, Ian. Yes, I really love the bulky old analog meters.....they just don't make them like they used to :)

[@ianbanhamamprepair9457]

That's for sure . Was a blast down memory lane for me ..re the meter ..

[@lukefenderrhodes]

uncle doug thank you for your videos they really have helped me on my way, with about thirty thousand people

[@UncleDoug]

You're welcome, Luke. Rusty and I are excited for the day when our videos finally reach one million views.....that's a long way off, but it will be a great moment :)

[@234dilligaf]

Very useful. I have an old original (two prong plug and all) Silvertone 1484 that I've been afraid to power up because it hasn't seen electricity in 20 years. I do have a variac. I wonder what duration of time would be appropriate to bring this amp up slowly to reform the capacitors? Caps look good visually.

[@UncleDoug]

I've heard of people who took DAYS to fully energize an old circuit.....which seems absurd to me. I'd give it an hour to go from 0 to 120VAC, but I would have a current limiter (see my video on how to build one) in series between the amp and Variac just to play it safe.

[@234dilligaf]

@@UncleDoug . . Yes I watched your video on a current limiter just yesterday, I definitely plan on doing that as well. I also saw your video on an ESR tester, and plan on buying one. Then I read your response to someone in the comment section to check ESR before bringing it up slow, and then checking again afterwards. I love watching your videos and really appreciate it.

[@UncleDoug]

@@234dilligaf You're welcome, 234. Good luck with your project.

[@donaldfilbert4832]

Great video Uncle Doug !! Not only did you debunk the naysayers on this issue; but once again demonstrated that it's best to see the truth of things for yourself !!

[@UncleDoug]

Thanks so much, Donald. Rusty and I really appreciate your kind and supportive words. Yes, whenever possible it's best to try to determine the truth, rather than accept hearsay :)

[@jensenbell]

Fascinating! Thank you! Maybe vintage amps wouldn't need so many Electrolytic Cap Jobs if techs would provide this service when you buy a vintage amp. Regardless, it's great to see myths put to rest with real testing.

[@UncleDoug]

You're welcome, Jensen. You are correct. The majority of my vintage amps have all or almost all of their original filter caps in place. The Variac and ESR meter (see my other videos) have changed my attitude regarding old electrolytic capacitors. Glad you liked the video :)

[@jensenbell]

Uncle Doug Thank you, sir. So far I have enjoyed every one. I am even sending them to my amp repair friends with the advice, "the next time someone asks so many questions that they are expecting you to be their professor free-of-charge, send them to KZbin and Uncle Doug for a primmer." I especially love how easy you make the math and reading schematics. My gratitude is hard to express fully.

[@UncleDoug]

Rusty and I sincerely appreciate your kind words of support, Jensen. It's great to hear that the videos are helpful and appreciated. Thanks, and best wishes from both of us :) ^. .^

[@jonathanhorne6503]

The two rectifiers you tested are directly heated. What about indirectly heated rectifiers like the 5AR4 or 5V4? Your tests confirm my findings. Btw, I usually use a 5T4 as a tester. Similar characteristics as thee 5U4 but only needs 2 amps on the heater. Works great.

[@kenfoland]

You could also install a NTC Thermistor (and bypass relay) in the supply rail to act as a soft start time delay. Then, it wouldn't be quite as troublesome.

[@UncleDoug]

Thanks for the input, Ken. The main purpose for a "slow start", which may take several hours, is to allow the electrolytic capacitors to reform prior to being subjected to high voltage. I don't think a Thermistor would serve the same purpose......however, it would be useful in place of a Standby switch in larger amps, particularly those with diode rectification.

[@kenfoland]

No, they wouldn't be particularly useful in capacitor reforming. But, for an amp that is in otherwise good operating condition, they do remove most of the impact of a full mains voltage start-up. They can also be useful in applications where filament flash at power-on (some tubes of European origin exhibit this trait) is a problem. Thanks, Doug. I'm glad to see you on KZbin again.

[@UncleDoug]

You're welcome, Ken. It's always good to hear from you.

[@seeburgm100a]

Great info.. the questions I'm looking for an answer to though are.. in a vintage hi-fi unit, let's say a McIntosh 240 (which is SS rectifier) and a McC20 Preamp would it be a good idea to power up with a variac on a regular basis with the thoughts of prolonging expensive tube life. Not a long slow turn up as used when checking equipment but rather let's say a gradual turnup over about a minute. Do you think this would extend the life of expensive power tubes and by turning it up slowly but not too slow prevent cathode stripping? Of course the Variac would have to be rated at a high enough number to supply the units being powered. Thanks Uncle Doug.

[@UncleDoug]

Not a bad idea, S100. Most tube failures occur on start up, and with a SS rectifier this is even more likely due to the brutally fast surge of high voltage. Another, easier but probably not quite effective method might be to use a current limiter to slow down the inrush of AC.

[@thome1547]

Well thought through video, informative as usual and a well brushed Rusty. Thanks and waiting for more.

[@UncleDoug]

You're welcome, TM, and thanks for the kind words. I think Rusty rubbed on some tree bark (like an old grizzly bear) and combed himself.....but he is looking a little better :)

[@carlrudd1858]

Hmmm...Hi UD....say, in one of my 'amp repair' books ( I won't mention names), it was explained that when bringing voltage up on guitar amps, which employ a tube rectifier, the tube should be removed and replaced with an octal base solid state rectifier for the gradual rise from the variac. I don't recall the explaination, altho I do believe they explained why. I purchase one of these 'plug-in' diode rectifiers and have been using it for years. What is your take on that idea?

[@andrecarvalhomusic]

Another great video!!! Uncle Doug, you're the best. Cheers from São Paulo, Brazil!

[@UncleDoug]

Thanks so much, Andre. It's always great to hear from you. Give all those beautiful Brazilian girls our regards :)

[@arnoldrimmer8008]

On Mr. Carlson's Lab's youtube channel he had a Thoradarson T20w40T amp that would spike voltage when powered on because the rectifier was directly heated and the pre-amp tubes were not. In that case it seems that you need to find a way to bring up the heaters in the the pre-amp section before you bring up the heater on the rectifier tube. He designed a little board to heat the pre-amp tubes before the rectifier tube. I guess it depends on the design but it's a pretty cool solution. I'd post the link but it is forbidden on youtube to do so,

[@UncleDoug]

+Arnold Rimmer Very interesting, Arnold. I am not familiar with that amp, but it may have a 5U4 rectifier (directly heated). A simple solution might have been to substitute a GZ34, which is indirectly heated and provides a very slow, gentle start up.

[@arnoldrimmer8008]

+Uncle Doug Hey thanks that should work. It looks like inrush inhibitors (soft start) don't do very much if the amp's power supply uses a directly heated rectifier tube.

[@UncleDoug]

This is just another reason why I prefer GZ34's to 5U4's.

[@fredbach6039]

Nice job, Uncle Doug, as long as people are using the 5Y3 or 5U4 or similar rectifiers. I noticed you didn't include a solid state diode assembly. In that case the B+ would start off right away but the various tubes would not. In that case, the B+ current and voltage might both be interesting to watch as the variac is cranked up.

[@UncleDoug]

I haven't performed this procedure with diode rectification, Fred, mainly since it is generally reserved for older equipment that used tube rectification.

[@BurtonBoyz715]

Great Video....I love Uncle Doug takes nothin' for granted. Test everything! By the by TempCo....makes a nice little Variac for $60.00 ~ or so...and there is a nice little video explaining its function...and Guitar Tube Amps applications in particular ... on KZbin here.....Just FYI

[@UncleDoug]

Thanks, William. Yes, I've been using Variacs for years, and just recently someone told me it was a waste of time with tube rectified circuits. Rather than quietly feeling like a fool, I decided to run an experiment to either verify my foolishness.....or prove otherwise. Unlike most experiments, this one came out in my favor :) Thanks for the info.

[@anaraug]

While it's is pretty important that you showed that a gradual rise on the AC corresponds to a gradual rise on the DC also, I'm still curious about when having a gradual DC rise is necessary. Is it only needed for old caps? Does it prolong life in new caps? What about old tubes and new tubes too? I'm not doubting your wisdom, I'm just still unsure which situations require the most care.

[@UncleDoug]

Walker, I think a gentle increase of DC is best for all the components in the circuit: tubes, resistors, all capacitors, transformers, etc., especially when they have not been used in many months or years. This is not just my personal opinion, but a standard practice for many, many years....starting with vintage radios and carried over to vintage tube amplifiers, and other vacuum tube electronic gear. It's why amps have stand-by switches and why GZ34 rectifiers are so highly regarded. The more gentle the start-up, especially the first one after long non-use, the longer the circuit components will last.

[@josquinmingus]

The joys and rewards of empirical science! I’m looking to buy my first variac. That’s a really nice Ohmite. Can’t find it anywhere. Did it come with that red case?

[@UncleDoug]

Yes, it was a gift from a good friend and fellow electronics hobbyist.

[@skycarl]

Thanks Doug, always fun, entertaining, and educational. Carl

[@UncleDoug]

You're welcome, Carl....glad you enjoyed it :)

[@Gizmopennington]

I wonder if you would have had different results with the rectifiers passing current on both amps if you brought the voltage up a bit slower to give the tubes a longer chance to heat up. You ramped them up pretty fast and the filament didn't get much chance to heat the cathode before the voltage was brought up higher! Just a thought... I have an Ampeg Portaflex B-12-XT guitar/accordion amp using an 5AR4 full-wave rectifier tube. It's been in storage for 30+ years and I'm getting ready to fire it up again. Just picked up an auto-transformer to bring it up slow. Let me know if there is anything I might need to look out for when I start the project. The amp was working great when it went into storage. I intend to put a three wire cord on it beforehand and disconnect the "ground" switch...would appreciate any comment on that as well! I enjoy watching your videos, Thanks for making them! Say hi to Rusty

[@UncleDoug]

Your observation is probably true, Gizmo. If I ever do this experiment again, I will allow the tubes longer to heat up. I would recommend a Current Limiter (see my video if you don't have one) whenever working on electronic equipment that has not been operating for a long time. It will protect expensive components, like the power transformer, in case a short circuit has developed over time. A three-wire power cord and bypassed ground switch make excellent sense.

[@Gizmopennington]

Doug, thanks for your response. I thought the auto-transformer (variac) would take care of the current limiting function. My plan is to bring it up slowly with a meter on the B+ just as you did in this video watching for any large draw by putting an amp meter in the on the supply line...should I also have the current limiter in the circuit? Also, there is a .047mf/1000v cap on the ground switch that goes between the chassis and the line. The switch alternately sends the line through the capacitor to ground. Should this cap be connected to the white (neutral) side of the line with a three wire setup or to the black (hot) side? Or should it just be taken out of the circuit?

[@UncleDoug]

Yes, you will also need a Current Limiter, Gizmo. A Variac will quite happily send its entire current capacity directly into a dead short, incinerating every part in its pathway. For current flow protection, you need a CL. The cap you describe is the so-called "Death Capacitor" which provides a means for electrical noise in the AC supply to go to ground before entering the amp circuit. You can eliminate it, if you wish, but the best solution is to install a 3-wire power cord that grounds your chassis, be sure you have a proper fuse in series immediately after the power switch, and then connect the cap to the black lead.

[@Gizmopennington]

Thanks much Doug, not sure where I will find a 250w incandescent bulb, but I assume I could wire a few smaller wattage bulbs in parallel to accomplish the same thing, is that right, or should it be series? There is a 4 amp fuse on the line, it actually falls before the power switch on the schematic, but the odd thing is the cap is shown on the ground switch (center) that falls before the power switch looking like the cap is always either connected to the neutral or hot lead of the power source depending on the position of the ground switch. If this is in fact how it is wired, I will rewire where the cap is on the other side of the power switch so it will disconnect the cap from the line! I have the original schematic that came on the inside of the cabinet. Again, thanks much for your help!

[@UncleDoug]

Gizmo, yes you can use 2 or 3 sockets in parallel and then screw in different wattage bulbs to suit the current demands of any amp you are working on. Many people like the fuse before the power switch, but it can make changing switches a shock hazard, even if the amp is switched "off". You should consider installing a 3-wire power cord, eliminating the ground switch, running the black wire through your on/off switch, fuse, and connected to your noise-filter cap (if you keep it in circuit) before going to the power transformer primary.

[@TheLittleFatGuy]

Doug , thank you for sharing all this wisdom , its really appreciated ! Thanks again !

[@UncleDoug]

You're quite welcome, FLG. Rusty and I are glad you enjoyed the video :) ^. .^

[@simonmavity180]

I have watched loads of your videos. really good style and I am learning so much. Thanks so much U D. :-)

[@UncleDoug]

+simon mavity You're welcome, Simon. Glad the videos are helpful :)

[@Barnekkid]

Good video and I really like having the information. Love the Simpson meter and the Ohmite.

[@UncleDoug]

Thanks, BK. They just don't make equipment like they used to :)

[@integra818]

Much appreciated this video. All the best!

[@UncleDoug]

You're welcome, Int. Likewise :)

[@bullthrush]

A great demonstration. I bet Rusty likes a slow wake up too :)) Late comment due to being on a camping trip.

[@UncleDoug]

Thanks, Andrew. Yes, Rusty does tend to sleep quite soundly.....but the trusty Variac always rouses him back to his normal, energetic self. Next time please schedule your camping trip so it doesn't coincide with the release of a new video :)

[@ericr5431]

I purchased a Ampeg V4-B head back in 1973. It was brand new. Paid $275. After 1 year the 40/70 cap in the power supply exploded. Makes me wonder how long it sat on the shelf. Makes me wonder if Magnavox burned the amps in before putting them on the market.

[@UncleDoug]

Greetings, Eric. I agree with you that the capacitors in a new amp should last more than 1 year. There can be several reasons for an electrolytic capacitor to overheat and burst, including a short within the cap (rare in one that's only one year old) or one downstream from the cap, drawing too much current through it (not the cap's fault). I hope you got it repaired and have had no trouble since.

[@ElPasoTubeAmps]

Doug - I think this is a very good video documenting what actually happens. Thanks - no matter what the empirical evidence is, it will be interpreted in different ways by different viewers. Even though I rarely power up equipment in this way, I think, overall, it is a good approach. It is kind of like opening a door that has been closed for 20 years. Wouldn't it make sense to open it slowly instead of just kicking it open and hoping the hinges don't lock up and break? I am not saying I will necessarily change my personal lazy ways of just plug-it-in and turn-it-on and replace-whatever-smokes :-) A second comment from a gentleman's posting below is, I would be Very careful in doing this with solid state amps Because... in a dual polarity amplifier (i.e. say, +- 40 volt PS), the bias voltages are going to be too low as the main power supply voltages rise and it is conceivable that excessive current could flow through the EC junctions of common BJT's and cause damage. Common silicon transistors are know as bipolar junction transistors (BJT) and they are current controlled devices in contrast to vacuum tubes as voltage controlled devices and the BJT's need all the voltages correct at the same time. So, just because this procedure is, as far as I know, fool proof in a vacuum tube amp, I would Not practice this procedure in solid state amps.

[@UncleDoug]

Thanks, so much, David. As my old granny always said, "When in doubt, run an experiment," and I know that you too heed this sage advice. I recall that in your workshop, we noted the "healing" properties of gradually charging old electrolytic capacitors. The ESR value might be rather high on a dusty old cap, but after charging it up a few times, the ESR value would drop way down to an acceptable level. I tend to view this soft-start method as a means to that end. Also, thanks for helping out with the solid state info below. I was not aware of the possible harm that a slow start might inflict on ss gear, and am glad the viewer received a knowledgeable, accurate answer.

[@rheidtech]

Interesting. Good stuff.

[@UncleDoug]

Thanks, RH :)

[@randolphpatterson5061]

ElPaso TubeAmps Has anyone ever made a "dummy" circuit so they could remove caps from an amp & hook them up to the dummy circuit to reform them with a Variac & a current limiter? Something like that could be a great piece of bench equipment!

[@ElPasoTubeAmps]

randolph patterson Well, I like that idea and I do not know of anyone that has built such a circuit. Unfortunately, many of the old electrolytic capacitors dry out and "open up" and for all practical purposes, don't exist as a capacitor in the circuit any longer. In these cases, people often times leave the big cans in the amp for cosmetics and just parallel in another capacitor under the chassis across the open-defective one. Electrolytic caps have a wet electrolyte in them that dries out and that is the end of them. They are not going to be able to be restored so a capacitor rejuvenating circuit might work on some but not on all.

[@brittisaacrossman]

Hello again Doug. I was curious if the B+ deflection could be happening at lower input voltages... might the rectifier not yet be warmed up enough to produce an electron flow? My logic is telling me that, given a simple system (no losses), you should have a relative input to output, and therefore would not have to hit a "target" input voltage to see deflection at the output. Does this make sense? Or am I just babbling again? Thanks for your time. EDIT:: I suppose that the purpose here is that you got gradual B+ at 30-40V range instead of the 100V input/B+ surge. I just seem to have gotten hung up on the mundane details instead of the main idea.

[@UncleDoug]

I think you're probably right, Britt. I noticed that even after I quit increasing the input, at 40VAC for instance, the B+ continued to rise for a while, probably due to the rectifier tube warming up. When using a Variac to soft start an amp, you generally increase the AC input very slowly and in small increments, unlike my demonstration (which had to be accelerated for the sake of brevity), and I will bet you that if you monitored the DC output under those conditions, it would begin much sooner. I tend to think there may be a threshold AC voltage before DC output begins, but it's probably lower than it appeared in this experiment.

[@Dan79istheman]

Great one Doug and Rusty!

[@UncleDoug]

You're still the man, Dan. Thanks so much. Glad you enjoyed it :)

[@germansanchez3577]

Hi uncle Doug THANKS for so many great vids on vintage amps thanks to this videos i was able to resusitate my first 2 gitar amps that i ever had , and i thougth i never use again!!!! any way, i will be looking foreward to your next videos.

[@UncleDoug]

You're quite welcome, German. Best of luck with your amp projects.....and be sure to see the video showing how to build a Current Limiter. It's a great device to protect vintage electronic gear after you have resuscitated it with a Variac.

[@galactictravels224]

Hey Doug can you damage an amp when playing on a Lower voltage

[@UncleDoug]

Probably not with a tube amp. With a solid state amp, it would not be advisable.

[@midmodaudio6576]

@@UncleDoug Does this mean that solid state amps should not be brought up slowly with a variac?

[@petarbursac76]

This is very interesting Doug. What if the amp has stand by switch? Should it be turn on?

[@UncleDoug]

If the only purpose of he slow start-up is to reform the filter caps, the stand-by switch could probably be off during the process. If it is to slowly energize the entire circuit, then the switch must be on.

[@jonsheehan4715]

Super informative! Thank you! I always wondered about this....

[@UncleDoug]

Glad you enjoyed it, Jon.

[@ironpirites]

Excellent video as usual.

[@UncleDoug]

Thanks, IP :)

[@brockerickson8696]

Excellent video. In your opinion is safe to use a variac on modern tube guitar amplifiers? Some modern amps may have digital electronics on board. I was curious if running a lower AC voltage to the amp may harm these electronics.

[@UncleDoug]

Brock Erickson Thanks, Brock. I understand that in some cases, particularly with solid state (digital, transistorized, etc.) circuitry, operation at low voltages can cause harm. For that reason, I would only advocate using a Variac on older, purely tube, equipment such as guitar amps and radios. This is discussed in comments below and in the video description. Quite frankly, since the slow Variac warm-up is to rejuvenate vintage equipment that has been dormant for many years, I fail to understand why anyone would even consider it for use with modern, digital devices.

[@brockerickson8696]

Uncle Doug Thank you for your response. I ask this because putting a variac on front of a tube guitar amp while playing may give the amp a more desirable tone. Eddie Van Halen claimed he did this to his old Marshall Plexi 100w to get his early era "Brown Sound" guitar tones. Around 88v. Thank you for your time.

[@UncleDoug]

You're welcome, Brock. That's an interesting story about EVH. I can see why they'd call it "brown sound".....sort of like the brown-outs that happen occasionally in big cities.

[@santacruz3600]

Dear Doug, I’ve only just learned about the concerns of powering up amps that haven’t been on in years. I have a few amps built in the early 2000’s that I haven’t powered up in 5 or 10 years. Would you recommend I buy a Variac and following this procedure? Thank You

[@UncleDoug]

I have two Variacs, SC, and I don't use either one to slowly energize old, fallow circuits. In my experience, all you need is a Current Limiter with an appropriate-wattage bulb.

[@rheidtech]

Hey doug. Nice to see ya. Were they talking about the b+ voltage starting at 100v+ at the caps maybee? Like we see here? Not ac volts? With the amp not reacting until 35vac the output the caps see is about 100 volts all at once? In a perfect world disconnect caps and bring them to life directly with the variac and bridge rectifier? This is what we do to warm caps up that have been sitting on the shelf when replacing ones in large vfd's.

[@UncleDoug]

Greetings, RH. I got the impression that the B+ would not appear until the input AC was rather high, and that it would not gradually ramp up, but would suddenly appear and rapidly surge to a rather high level.....completely unlike what I found in the experiment. To be honest, I think that the DC would actually appear much sooner than 35VAC, but that it was delayed until the rectifier tube cathode could warm up a bit. I'll bet if you re-ran the test with a warmed-up rectifier, the DC would appear at a lower AC input level.

[@rheidtech]

Yes. Probably UD. Great experiment.

[@mixolydian2010]

Thanks a lot Doug, great to have more videos from you all the best to you and Rusty. Colin...any luck with the adineko?

[@UncleDoug]

You're welcome, Mix. For those not familiar with the Fender Adineko, here is a site: www.eddievegas.com/store/details/1965-Orig-Fender-Echo-Reverb-Oil-Can-Adineko-Tel-Ray-Electronics-LA-CA-Made.php

[@barrywuthrich8530]

I don't own a variac. Someone gave me one once and I had no idea what to do with it, so I gave it to a tech friend of mine. I since have built a current limiter and am thinking it may be time to get a variac. I know of one for sale locally for $30, but it is only 500VA. Is that enough for working on tube amps? I noticed some of them are 2000-3000 watts, but I don't know what is enough.

[@UncleDoug]

I rarely use my Variac, Barry, but certainly would not advise that you not get one. The unit you mentioned sounds like around 120VAC @ 4A max, which would probably suffice for tube amp work, since most draw around 2A or less.

[@randolphpatterson5061]

Uncle Doug, can you help me with a couple questions? I have recently acquired a Silvertone model 1481 guitar amp. I have had Gerald Weber's book and the Groove Tubes book by R.Aspen Pittman for about twenty years and have read through them numerous times. I paid attention to the sections describing power cap reforming. I felt that I was long familiar with the cap reforming procedures, and I didn't look through these books when I decided to try my Variac for the first time a few weeks ago. After cleaning the amp up a bit , I pulled all the tubes from the amp, and hooked up the Variac. I didn't hook up any of my meters, but my Variac has the built-in current meter, which never indicated much current the entire time, as I expected. I ran the Variac at around 30 volts for a few days and then increased it by ten volts about every other day. I recall that the books said that after a day, the voltage could be raised ten volts every hour or so, but I have other things going on and this is being done in my home, so I wasn't keeping a constant vigil on the amp. I had it up to 120 volts a few days ago, and then shut it off, and I haven't re-tubed it yet. Since I'm still new to the internet, I just stumbled on to your videos today. I saw your clip here, and I noticed right away that you didn't remove the tubes for this demonstration. Did I not need to bother removing the tubes? And might it be that the power multi-cap in the amp wasn't being reformed if I didn't have the tubes installed? Or does it not matter either way? I try to do any of my amp work the best way I know, and since this was the first time I did this, I admit I should have reviewed the procedures in those books before operating the amp. Am I good to go, if I power up the amp and play through it? or did pulling the tubes negate the effectiveness of the reforming procedure? Did I harm anything by doing this? Okay, that's more than a couple questions...

[@UncleDoug]

randolph patterson Greetings, Randolph. I'm sorry to say that if you did your slow start-up without the 6X4 rectifier tube in place, you accomplished very little because there was no high-voltage DC produced to reform the filter caps. I think your best bet would be to build a Current Limiter (see my video on how to do this) and use it when you first power up a newly acquired amp. It will protect against any internal shorts causing component damage, and the amount of glow from the bulb will indicate current flow. Any un-shorted caps will reform (their ESR values will decrease) while the circuit is energized. It's not as gentle as a Variac warm up, but produces about the same result much more rapidly.

[@djfrank59]

Uncle Doug You could also put the current limiting light bulb on the load side of the Variac :)

[@michel333100]

Hi Doug, I wanted to ask you a question about variacs. I was thinking of buying a 5 Amp 500 watt variac. I read on the net that people were using variacs for live performances with their guitar amps to slightly lower the voltage in their amps to sometimes get a browner sound out of their amp or just to go a little easier on the amps valves and components. I was interested in doing this because I have a 1965 Fender Bandmaster amp. Do these new variacs need to be grounded by a tech or anything like that firstbefore running them to play your amp through? Or can you just buy one of these variacs like the one I mentioned, a 5 amp 500 watt variac for a 50 or 100 watt amp. The amps that I have are either 3 amp, 2 amp fuses or a Mesa Boogie Tremoverb amp combo at 100 watts uses a 4 amp fuse. There us a guy in the States there that sells a type of transformer box called the RXamp Brown Box wher you cn just plug this thing in and lower your voltage in your amp to say 110 volts. Just plug and play. No worry about it damaging anything or getting electrocuted. Just one draw back, It's $500.00 for one these in Canada. Would a variac be a safe idea for running your amp at a lower voltage? Thanks Michael Newell from Niagara Falls, Ontario, Canada [e-mail]

[@UncleDoug]

Yes, you could run an amp through a Variac, just like Eddie Van Halen did, but there would have to be a 3-wire power cord to the Variac and a 3-wire socket for the amp....with chassis grounding tested and verified. Second, you would want some leeway in current capacity. Running a 4 Amp circuit through a 5 Amp Variac for a long period of time might cause some overheating (in the Variac) and possible (disastrous) failure. If you are going to use the Variac over extended periods, get one with a minimum of double the current capability you will need. Good luck.

[@michel333100]

@@UncleDoug , thanks very much for your advice Doug. Hope you will always continue to make great videos. I wish I had the cash to take a trip down your way. The looks fantastic. Buried in snow here now. Take care, thanks very much.

[@UncleDoug]

@@michel333100 You're welcome, Michael. It was in the low 70's here today. I rode around in one of the hot rods in a T-shirt with the windows open :)

[@howardskinner4916]

Love that Simpson volt meter!

[@UncleDoug]

It's a pawn shop find, Howard.....for $15 in mediocre condition.

[@fostexfan160]

Very informative and excellent presentation....... On the subject of a variac, I want to slowly power up the filter caps in a Fender pro Reverb, the variac in question has a power rating of APS 500 watts with a 2 amp current rating. Would this be a suitable variac? Many thanks for any advice

[@UncleDoug]

That's a rather small Variac, FF, but since the Pro Reverb comes with a 2A fuse, I would think that the amp's current draw must be within the working parameters of the Variac.

[@fostexfan160]

@@UncleDoug Many thanks .......your videos continue to inspire this fascinating subject. Long may you continue

[@UncleDoug]

@@fostexfan160 You're welcome, FF. We appreciate your nice comments.

[@stevenpierce8331]

Uncle Doug, you are just Awesome \m/

[@UncleDoug]

Thanks so much, BB

[@etuning6478]

Uncle Doug Would I use a Variac to bring up my Peavey Solid State Amp (it is a Express 112 -65watt) filter capacitors or would that just be a waste of time of course there are no tubes involved here. Thanks

[@UncleDoug]

+E tuning You could do a Variac slow warm-up, ET, but it's only beneficial if the amp has been dormant for several years. I also always recommend using a Current Limiter when first energizing any old amp that has been sitting a while. Good luck.

[@etuning6478]

+Uncle Doug Thank you for your reply I will build your Current Limiter project thank you very much

[@UncleDoug]

You're welcome, ET. I believe you will find the CL to be one of your most useful tools. I use mine with every amp that I work on.

[@rbauer1632]

Thanks for the experiment. I built a current limiter that uses a light bulb to detect any shorts in a circuit. Later I came upon an article that mentioned using just such a limiter, but they also claimed that it acts in much the same way as a variac to slowly charge the capacitors. Do you think this is true? Of course you have no dial to regulate the voltage, but do you think it would charge the capacitors at a more gradual rate?

[@UncleDoug]

Greetings, RB. I would think that a Current Limiter might slow down the charging process by a small amount, i.e by a few seconds, but it wouldn't come close to the rate reduction you can achieve with a Variac. I use a Current Limiter on a daily basis when working on amplifiers, to prevent damage to components in case of a short circuit. The Variac is better at re-forming electrolytic capacitors. To me, they serve two completely different purposes. Thanks for your inquiry :)

[@tubical71]

Something leaps in my mind: *DO NOT* repeat this here....*DO NOT* use this method in anyway when you got a rectifier like *3B25 -- 3B28 -- 866 -- 866A* or similar present in your Amp and/or Radio Again: *DO NOT* use a *variac* with a vapour rectifier tube. They *WILL BLOW UP* these tube need to be preheated before the B+ is applied. With the variac you´re foolin´ (=messing up) the old preheat section. The plate voltage will be present at the plate and let this rectifier tubes simply *explode*! You *DO NOT* want this, as the mercury will be come off that tube and that is in no way something what you want to have next to your bench, trust me!

[@djfrank59]

Mercury Vapor rectifiers are quite the different animal! When I encounter amplifiers with MV rectifiers, I do not use a Variac. I usually pre-heat the tubes for 20 minutes from a cold start after the amp has been sitting for some years. I've worked with Mercury Vapor Rectifiers for many years in AM transmitters and large tube power amplifiers. MV rectifiers are good rectifiers due to the low voltage drop they have, but when they go bad, most of them tend to short. I worked at one AM radio station where the transmitter had pre-heater sockets to keep the new spares warm and ready in case of rectifier failure. I have a few Altec power amps that use 4 866A's in each. the 83 is also an MV rectifier which was popular in early tube testers. I have a pretty good supply of NOS 3B25, 28's and 866A's.

[@djfrank59]

Frank Ferraro One of the important things to remember if you're building an amplifier using 866A's is, they are best to be used with chokes as opposed t electrolytic caps. the other downside of MV rectifiers is, the RF noise they generate which can get into the other stages of an amplifier. Lead dressing and distance from signal input/output is important to remember...:)

[@tubical71]

....the DCG i´ve shown in some of my videos is the better known version of the 3B25/866A....it is 2kV/0.5A rated for cont. ac service. Easy to mount as the socket is a standart light bulb thing:)

[@UncleDoug]

Again, great advice, especially for those of us who wouldn't know a mercury vapor rectifier from a Mercury stationwagon :) Viewers should be certain that the rectifier they intend to gradually energize with the Variac is a conventional tube rectifier, not a mercury vapor rectifier. If in doubt, check a tube handbook or the Internet to verify rectifier type.

[@djfrank59]

Uncle Doug Excellent advice Uncle Doug! You can download the entire RCA tube manual for free on the net which will give you characteristics of just about any tube...valuable information for someone who is working with vacuum tubes! :)

[@charliefoxtrotthe3rd335]

Is that really true? That old electrical components can be be damaged if left dormant for a long period? When my grandfather passed, I got his beloved old Gibson Lancer. You may have heard of it, it's kind of an obscure amp, but it sounds so good, even after all these years. Of course, I am ignorant of all things electrical, so I never gave using it a second thought. Now, I am wondering if I did some damage. He could not play his guitar for the last 15 years of his life, and it sat another two years before I got it. I did take it in and have it looked over, but he said nothing of using a Variac to bring it back to life.

[@UncleDoug]

Greetings, Danny, and don't worry. If the amp worked fine for you, you did no damage.....believe me, if an electrolytic capacitor (EC) had shorted out, you would have known it. Of all the components in an amp circuit, the EC's are the ones that actually deteriorate with time and lengthy non-use. If you catch them soon enough, they can be rejuvenated either by use (as you did) or gently with a Variac, as in the video. If they have deteriorated too far, nothing can save them. With an old, original amp like the Lancer, continuous use will probably keep the EC's in good shape.....but, if you want to keep it original and protect it, you should build and use a Current Limiter (see my video on how to build one). It will protect the amp components in the case of any short circuits, especially on start-up, and will immediately alert you by flashing brightly if a short circuit occurs anywhere in the amp. Good luck :)

[@randolphpatterson5061]

Täking Thë High Roäd You might have just got lucky. Maybe it was a case of being stored under rather ideal conditions. I do remember the Lancer, and I have a Discoverer Tremolo that I used as recently as the 90's, and it worked great. Class AB1, two 6BQ5's (EL84's), and a tube rectifier. Model number GA-18T. I ordered a set of power caps from MCM, but just sat on things when I found out I could get multis. Back burner special, I should've just left it alone & kept playing it. Back when I got it I had to put a speaker init, and came up with a Fender Jensen. The amp never failed, I was just looking to install fresh power caps when I took it apart. I am so bad at finishing things of my own, when I am working on somebody else's stuff, my personal amps get chronically neglected.

[@charliefoxtrotthe3rd335]

randolph patterson When I got it back from the guys at the shop they said that they have never seen an amp in that good of shape in the 30 years they had been repairing vintage amps. Every single component looked as though it had just came from the rack. Even the two pronged plug with the cloth cover was like new. They did a few things to get it up to code, like replace the cloth cord with a modern three plug and grounded the amp properly. And replaced the tubes just because they were so old. But they gave me the old parts to keep so that I could restore it back to original vintage if a collector demanded it. But that Discoverer was a real gem too. I have heard of them, but never played one. Good luck with your new caps.

[@daviewavie112]

I have a 5amp Variac. Is that sufficient for bringing up tube amps? I have a pair of 30watt monoblocks and I built a light bulb current limiter to use in conjunction with the Variac. Just wondering if 5amps is enouigh

[@UncleDoug]

Check the fuse value for the amps you intend to use the Variac with. Odds are they are less than 5A.....so your Variac will work fine with them. Any that have fuses greater than 5A might not be suitable.

[@anotherOneMore7]

What is the minimum specs needed for a variac to be used for tube amp repair (U.S.)?

[@anotherOneMore7]

What I meant was do I need a 3 Amp, 5 Amp, 10 Amp, 20 Amp for tube amp analysis and repair? I am going to guess 5 Amp.

[@UncleDoug]

@@anotherOneMore7 5A would be more than enough in most cases, but it's a good choice. Most amps are 3A or less.

[@JTM45100]

Do you have to have all the tubes in to do this or just the rectifier? There is another method some of my friends who work SS rectifier 100 watt Plexis use on vintage and new builds. They put a big resister between the rectifier bridge and mains. They measure the voltage drop across it. At first it will be higher, but with time it will decrease. This can take as long as 24 hours, but when done the caps are formed. On new builds the time is quicker. The guys that do this swear by it. They say it helps with making the amp very low on noise.

[@UncleDoug]

In this demo, JTM, all the tubes were in place. This best represents normal, working circuit voltages and current...and I was more concerned with demonstrating that the DC voltage is created at low AC input levels, despite opinions to the contrary. I guess you could perform the procedure with only the rectifier in place. The inserted-resistor method you describe is an excellent way to not only re-form the filter caps, but also test them for leakage (without requiring special test equipment). I may make a future video demonstrating this technique. Thanks so much for your input :)

[@JTM45100]

Uncle Doug I can't wait to see that video when you make it. Thanks for the reply and the time you took to make all these videos. I really enjoy them.

[@UncleDoug]

You're welcome, JTM. We'll try to get it out in the near future :)

[@donaldfilbert4832]

Uncle Doug I'd like to see that video !!!

[@UncleDoug]

Stay tunes, Donald. It's high on the list of prospective videos.

[@tubical71]

I demand a show-case video of this "Zenith" Amp chassis, Doug....come on, nice stereo thing, don´t let us down here;)

[@UncleDoug]

You read my mind, TC. I already shot some video of it, to be part of a larger video that demonstrates the incredible electronic equipment bargains that are available at garage sales and thrift stores. This Zenith chassis has a full complement of matched Amperex tubes (4 x 6BQ5 !!!), a big, stout power transformer......and the (new) owner bought the entire stereo unit at a garage sale......for $15 !!!

[@tubical71]

You know my words...;) I do not want to hear that bargain thing. The last tube "bargain" that i came across here last week was a non complete chassis with a blown mains tranny for $50, he did not sale it anyway for that prise, but these are the average money they ask today for tube equiped units. As when people see tubes inside they see themselves getting some $$$ as well. So no more bargains here.... Next real bargain i get, i´ll post a video on it.

[@daviewavie112]

Do you usually bring up tube preamps on a Variac as well? And do they need any sort of load like tube power amps need a speaker load? Also, I read a lot about using a Variac to bring up an old tube amp slowly, but what about in every day use? Is it best to actually use the amps through a Variac all the time after the first initial turning on?

[@UncleDoug]

I don't build pre-amps, David, but if I had an old one with its own power supply, I would probably start it up initially with a Variac. You really don't need to slow start any amp that has been used in the past year or two.

[@diceman220]

I was told you can change the tone of an amp, by lowering the voltage. Is that true? Also voltage can it vary from place to place? Thanks

[@UncleDoug]

Rumor has it that Eddie Van Halen used a Variac to reduce the voltage level to his amp and achieved some sort of "brown sound", but I have never tried this myself. I'll bet, however, that there are videos purporting to demonstrate this phenomenon. Yes, voltage levels vary at different times of the day and in different parts of the country, but only by a few volts, which doesn't make an audible difference in a guitar amp.

[@BicycleJoeTomasello]

Hello Uncle Doug, Thank you for this and all your video's one more time in case Rusty wasn't listening the first time. Question please,what size Variac do you recommend for amp testing and electrolytic capacitor reforming? I doubt anything over 50 watts would ever be on my bench but you never know when a Marshall Major might walk through the door.

[@UncleDoug]

You're welcome, Joe. The Variac in the video is an Ohmite V.T. which outputs 0 to 140VAC at a maximum of 8 Amps. Most amplifiers that I work on are happy with 120VAC and less than 2A input, so it's more than adequate for my usage....and probably yours too.

[@djfrank59]

Uncle Doug A standard Variac that's popular on most tech benches are the typical 500VA units which are quite suitable for average tube amplifier and radio service, however, I had to bite the bullet and get one of the big boys (20 amp) units for servicing the bigger tube amps, SVT's, Messa Bass 400's, etc. and occasionally a Fender 400PS. Since these amplifiers operate at insanely high B+ voltages, I wouldn't chance just plugging in an amp if the problem with it is unknown, or the customer is unclear of the symptoms or if he even knows the history of it if it was newly obtained.

[@huberttremaine8343]

Is there a self life for caps? How long will they last, brand new and never been in service. Last summer I went to a yard sale and found a box of electronic parts and there were caps that were new(no solder) or in parts bags. I gave 5 bucks for the whole box! Thankz

[@tubical71]

Hi Hubert, of course there is a "lifetime" for Caps. Industrial grade Caps usually got some readings like this (this is an example of one of my caps lying around) 27/105/56 besides the usual: 180/385/400 and 06/98 What are their for: Operating (ambient while working) -25 up to 105 gedgrees celsius within 56 days of humidiy tested in a climatic controlled enclosure (temp oven) Next is: 180 usually in micro farads (=capacitance) 385 is the max operating voltage 400 is surge limit peak voltage of about half a cycle. Last is the datecode here it reads 06 for week and 98 for the year (=06 week of 1998) According to the IEC standard for Caps they do test on how long the operate, some first grade Caps have lifetime rating printed on as well, like this: 105/10.000 the manufacture garantee that this cap will be last at least 10 thousand hours of service (also known as the MTBF=MeanTimeBetweenFailure) at 105 degrees celsius without driyng out more than 20% of the initial capacitance. More "sophisticated" Caps reds this: 135/20.000, or 40/135/85 If you go for filter caps, if they are not dryed out or leaked physically you can try to "re-form" them when you have some NOS or pre-used (big)filter Caps: Apply a DC voltage with current control. Rise the voltage very (about 5minutes) slowly up to the rated voltage, but watch the current. Use an analog meter for that as the reading is far more clearly when current may change rapidly. When you charged the Cap completely just shut down and leave it like this for a while (over night), as the static voltage in the cap causes some chemical procedures inside and also re-format the insulation, but this takes time. I was able to re-format some very old NOS Caps and now they are working just like new ones within their ratings. As well as industrial grade LowESR 2200/500/550 25/105/85 08/76 with M8-screw terminals. But be very careful with Caps that size, as they store a *huge* amout of energy. *do not* touch the terminals in anyway, *never* short them. And store these caps with a 470k to 100k resistor across the terminals. As even a fully (=close to zero volts) discharged Cap will do some "self recharging" over time causing some real lethal voltage presented at the terminals.So if you find some of these, may be in a box or some online auctions in unknown condition *never touch the terminals* measure the voltage first! Hope this helps;)

[@djfrank59]

TubiCal I keep large bleeder resistors on my bench with clip leads attached to them...a valuable discharge tool.

[@UncleDoug]

TubiCal Great advice and information. I too have noted the mysterious "self charging" phenomenon. During the experiment in the video, after carefully and thoroughly discharging each filter cap, I noticed that the (B+) DC voltmeter (which was at zero immediately after the discharging process) registered a slowly increasing voltage, even though everything was turned "off".

[@djfrank59]

Uncle Doug By the way, I had to take notice to the Simpson 260 VOM...Looks like you've brought it back to life! :)

[@UncleDoug]

Yes, it cleaned up perfectly, inside and out, and seems to function quite well. I know that digital meters are the standard of the industry, but I still REALLY like good analog gear.

[@timpayne8238]

Is this method ok for solid state rectifiers?

[@UncleDoug]

Yes, in fact it may work better with SS rectifiers than with tube rectifiers, since the tube rectifiers may not start producing DC until the input voltage level reaches a certain threshold.

[@elwrongo]

"so you're roaming the local pawn and thrift shops and comeup with this nice early 1960s Gretsch 6150 amp.." hahaha, what kind of heavenly world is this you live in? I need to go there now!

[@UncleDoug]

Don't laugh, EW. I also turned up a nice Gibson EH-150, GA79RVT, and a mint 60's Supro with the owner's manual still inside......not to mention an American Strat that they thought was Chinese, for $179.

[@elwrongo]

@@UncleDoug I have to laugh Uncle Doug otherwise i will just start crying :)

[@fbetti9]

Indeed very instigating - great food for thought! However I might say that it could've been much more enlightening if not only directly heated rectifiers had been addressed. What if I'm using a 5V4 or a EZ81/6CA4? I'd rather go along with reforming electrolytics by using a regulated external power supply direcly attached to the filter capacitors while everything else is turned off instead of fooling around with underheated filaments and/or heaters as none like such treatment! Not to say the low pressure mercury rectifiers - read further looking for valuable TubiCal comments and stick to them!

[@UncleDoug]

To each his own, Flavio. Thanks for your input :)

[@kevinbyrd6482]

where"s those video" of your sandrail you were working on.

[@UncleDoug]

I did record some video of the sandrail in action in the desert, including some scenes with Rusty, but hesitated to post it for fear that it didn't coincide with the interests of most viewers. Who knows? I may do it anyway :)

[@gennidee]

Bare in mind that you turned up the AC quite fast and hence didn't give the filament time to warm up, which it does even slower at these low voltages. I don't expect to get DC output at very low voltages since the filament has to reach a certain temperature in order to generate enough mobile electrons that can travel to the anode. But I think if you had turned up the variac ever so slowly you would have seen DC at much lower voltages. Especially on the 5U4 you see that once DC comes up it rises quite fast without turning the variac, which is due to the heater just starting to kick out more an more electrons that can be attracted be the anode. Maybe try doing this test backwards and see when the tube heater is too cold to produce mobile electrons or dial in a much lower voltage, say 20VAC, and wait if the DC comes on. If not, increase to 25 and wait again...

[@UncleDoug]

+GenniDee A very interesting observation, GD. When I get a chance, I'll check out your suggestions. Thanks for watching and commenting :)

[@gennidee]

+Uncle Doug You're welcome (: And thanks for your very interesting videos! They inspired me to dig out my soldering iron again after some years of not building amps and I'm currently working on a small use-only-junk-parts-project ^^

[@UncleDoug]

You're welcome for the videos, GD, and it's great to hear that you're back in action. Best of luck with your new project :)

[@makemyday2560]

Thanks...! Great demonstration

[@UncleDoug]

You're welcome, Rick......are you feeling lucky ??? :) :) :)

[@makemyday2560]

Thanks Uncle Doug..! Yep.. every day I wake up.. I am LUCKY..!

[@UncleDoug]

At our advanced ages, Rusty and I feel lucky to wake up too :)

[@GregsGarage]

I love this kind!

[@UncleDoug]

Greetings, Greg. It's good to hear from you. Glad you liked it :)

[@68MalKontent]

Very informative, thank you for the experiment. Empirical approach rules :)

[@UncleDoug]

You're welcome, Stan. I think it's always preferable to design and perform an objective experiment, rather than simply accept hearsay.

[@fullwaverecked]

Hello Uncle Doug, I have a question that is off this topic. I get amped up watching all your videos, and all the other usual suspect giants on KZbin. I'm trying to learn as much as I can about vintage tube gear. Last month I bought a Earth 440 Amp head. I didn't know anything about it, but for $30.00 I couldn't resist. I plan to bring it back to life. So, my question is: in your opinion, why are solid state Amp repair videos almost non-existant on KZbin? Are SS Amps horrendous compared to tube amps? I plan to make my first KZbin video this fall with the Earth Amp head. Your feedback, and anyone else's, would be greatly appreciated. Thanks!

[@UncleDoug]

I wasn't aware that SS videos were in short supply, FW. They are generally no more complex or difficult to repair than tube circuits, and they operate at lower voltages, but tube circuits are "in" at the moment and thus apparently in high demand for video coverage. Perhaps you can become the SS circuit guru on YT. Good luck.

[@fullwaverecked]

Uncle Doug Thanks for the info/advise! I've been watching/studying you, Brad, Paul, El Paso, etc. etc. for years. Three months ago I saw a Earth Amp head (440) 1976? for sale, local, and for $30.00, down the rabbit hole I went. Insidious, yet deliciously painless is the Amp bug's bite? So long story short, I've since been vintage test gearing up to perform a full physical on the Earth Amp this fall. It will be my first KZbin video, and thanks to you and many others, there's a modicum of a good chance I won't look/sound like a clown doing it. I've been googling the hell out of this Amp head - Peavey clone - and it doesn't seem critical to keep it religiously original? If you have any thoughts/advice regarding modifications that would make the Amp Head safer, perform better, I would greatly appreciate your input. AFTER you finish part 2 of the Viciously Awesome Amp Eater video, that is! Thanks again, and best wishes!

[@UncleDoug]

You're welcome, FW. As you commented above, answering viewer questions has become a very time consuming task, leaving little time to assist others with their projects. My advice would be to incorporate what you have seen and learned into your video evaluation of the EA head. You will gain more from the process if you do it yourself. Good luck.

[@fullwaverecked]

Uncle Doug The best advice by far. Thanks again!

[@UncleDoug]

You're welcome. Good luck.

[@Mattstiless]

Excellent vid I loved this

[@UncleDoug]

Thanks, Matt :)

[@cyberquipment99]

Good demo

[@UncleDoug]

Thanks, Roger.....glad you liked it :)

[@michaelalbro6856]

Uncle Doug has more patience than I do, if I’m right and I know it, I wouldn’t take the time to prove it to anybody who didn’t believe me.

[@UncleDoug]

Thanks, Michael.

[@JCHaywire]

A triumph of empiricism!

[@UncleDoug]

I doff my mortarboard in appreciation, JC :) It's always good to hear from you. Thanks for watching.

[@jazzgtrs1243]

Your videos wouldn't be the same without Rusty's finishing touch :)

[@UncleDoug]

You're soooo right, JG. His distinguished canine presence never fails to elevate a dry technical presentation from mundane.....to magnificent :)

[@RODALCO2007]

Interesting video.

[@UncleDoug]

+RODALCO2007 Thanks :)

[@russbrooks3510]

well done. thank you!

[@UncleDoug]

You're welcome, RB.

[@dwightbehm2886]

Uncle I gota say. Who cares about greed and if its an anteque or how old it is. sound is perseption. It can be Recreated nomatter. The materials you and I know that.money comes and goes. You cant take it with you when you and I are gone so whats the point? You are a great Teacher. The love of money is getting dumn Now days. Challenge Question? Does a modern day 2020 year all Tube amp sound any better than any anteaque amp?

[@UncleDoug]

As a retired school teacher, I am qualified to speak about a lack of money......and I consider it to be an asset rather than a liability. As a result, I am much more creative and appreciative of the things I build and the things I can afford to buy. I have not heard many modern amps, Dwight, and thus am not qualified to make comparisons......but I'll bet there are some that sound every bit as good as the vintage amps.

[@bradbeasley7669]

jack says thumbs up

[@UDX-21]

Thank you!

[@UncleDoug]

You're welcome DD :)

[@BourneAccident]

I think Rusty seemed disinterested because he "might" have been waiting for a test with a GZ34 rectifier, even though the results would probably be similar.

[@UncleDoug]

Bourne Accident I imagine a GZ34 would behave about the same, BA. Rusty is so fond of the tube that he named one of his puppies after it.

[@raymondheath7668]

The detractors of slowly ramping up a voltage on a rectifier, or any tube for that matter, do not understand that a tube is a linear device, not a switch like a semiconductor

[@UncleDoug]

I believe that most tube rectifiers have a threshold voltage, Raymond, below which, they do not function. Once you reach the threshold, they do tend to respond in a linear fashion.

[@raymondheath7668]

Uncle Doug yes, the electron build up on the cathode and the plate voltage sufficient to attract them

[@sfmag1]

Simpson 260! No mirror though.

[@UncleDoug]

Yes, from a local pawn shop.

[@surgingcircuits6955]

Can I have your Simpson 260?

[@UncleDoug]

Check your local pawn shops, SC. That's where I found mine......for $15.

[@surgingcircuits6955]

@@UncleDoug Wow!

[@jeffb6161]

great video, love the simpson meter

[@UncleDoug]

+jeff b Thanks, Jeff. It's a great meter. I found it in a pawn shop in filthy, non-working condition, for $10. It cleaned up to be just like new.

[@jeffb6161]

most people forgot what good sound is, good sound in my opinion is reproduction of sound as close as possible to being right in front of the band live or in the studio. and my RCA does it very well. or any halfway decent tube amp. they forgot what good equipment is too, like your simpson for instance, you could have dug it out of a hole in the ground 40 years later and probably still cleaned it up!!! the ryobi is interesting did not know they made them, have the lithium drill and circular saw and hold them dear to my heart!!!

[@UncleDoug]

I bought the Ryobi multimeter as a result of being disgusted with the flimsiness of my old unit.....it is very robust and seems to be quite accurate. I know it's not a Fluke, but it works for me.

[@bobbarcus8310]

Is that simpson a VTVM..And I wish you would show us novice guys how you hook all that stuff up so you do not KILL us dumbass's..lol I know you think you are only talking to people who know what they are doing...I have learned a lot more than I did from all your great vids...

[@UncleDoug]

Bob Barcus I realize that many viewers are novices, Bob. Learning how to operate a complex measuring device like the Simpson meter (it's not a VTVM.....it does not use AC power or contain a vacuum tube) is like learning to play the guitar. People can tell you how to do it, but the best way to learn is simply to get one and experiment with it on low-power circuits (at first) and then gradually move up to higher voltage circuits, like tube amps. Most meters come with detailed instructions, and much info is available on the Internet. I'm glad the videos have been helpful.