Fender Amp Vintage Bassman Cap replace and repair

[@luizdejesus6240]

Good work on the amp. I would suggest the hot (black) should go to the fuse first (center) then the power switch in case of a switch failure. Also, the ground should be left long so that it is the last wire to get disconnected if the power cable is accidentally pulled out of the amp. Finally many techs prefer to solder the green ground to the chassis instead of drilling holes. The terminal is only stripped and crimped, it can corrode and the nut can loosen with time...

[@richardharris3426]

Si o al menos estañar la punta del cable de tierra para luego insertarlo en el conector. Hubiera quedado una conexión más rígida y sin peligro de que el alambre de cobre se oxide. ¡Bien trabajo!

[@titusfive]

Thank you! Finally someone shows the actual process for those of use new to electronics repair. Every other video seems to avoid filming the de-soldering, cutting the wires to fit, soldering in the new cap, etc. Great video!

[@FrankOlsonTwins]

Thanks! Yeah, sometimes the hardest part of repair is de-soldering and removing parts without damaging the remaining components! It's a bit tricky because KZbin attention span is very low, so showing full repairs in real time would just be buried by the algorithm. I try to keep a few little "experience gems" in the video to keep the educational value high, but it's a tradeoff.... Thanks for checking it out!

[@FrankOlsonTwins]

I didn't want to add too much music to this, so there's plenty of silence between the commentary. More of "A picture is worth a thousand words" video this time. There's a working demo near the end as well.

[@zbaby82]

I like how you use heat sinks while soldering. Very professional.

[@FrankOlsonTwins]

Thanks! Like any surgery, rule #1 is do no harm...!

[@FenderFixer]

Overall, a beautiful job! However, the hot (black) lead of your power cord should connect to the fuse holder, not the neutral (white).

[@tjminasi1442]

Neutral should directly to the power transformer winding. It’s the safety code. Hot to fuse then switch and the other side of the power transformer.

[@tjminasi1442]

Little dab of silicone adhesive under the PS Caps would be a good thing.

[@YeatzeeGuitar]

Really great work here, this is a great resource for people. I try to show everything as much as possible but it's a tough balance. Curious why you didn't just solder to the chassis? A lot easier then drilling a new hole. You obviously know what you're doing, I can't imagine you don't also have a big iron available?

[@FrankOlsonTwins]

Thanks! I was taught to use a crimped eyelet with a dedicated bolt for Earth ground. Everyone has their own preference for these things and this is one I'm diligent about!

[@meesterprofe007]

Very well done!

[@FrankOlsonTwins]

Thanks!

[@rupe53]

Great video and very straight forward. Nice touch with the clips as heat sinks. So, I have one of these 67(?) Bassman amps and it's mostly original, other than a new power transformer and line cord maybe 15 years ago. The tubes are a mishmash of brands, but it has fairly new Sovtek 6L6s on the output. What brings me here is I recently took it out of storage, and it blew fuses on power up. I replaced the fuse with a slow-blow (spec on the rear panel) and slowly brought up the line power on a Variac, starting at 20 volts and ramping up to normal. No further issues so I suspect the old (OEM) caps just needed some TLC after years on the shelf. Does anyone offer a cap kit, or should I just make a list and go hunting? BTW, I am told my unit is in near pristine condition, other than a little road rash on the speaker cabinet from gigging back in the day. Any idea on street value for these things?

[@FrankOlsonTwins]

Prices for Bassmans hover around $1k. Some go for more, other's less depending on a number of factors. Ironically, the speaker cabs don't add a huge value to the cost since the days of lugging around big cabs have basically passed. Variac is always a good idea after a long period of sitting. However, I usually do recommend replacing all the electrolytic caps(even if just in the power supply to start) on vintage units. My rule, especially with vintage gear, is the second you hear hum, shut it down and service it. As far as caps suppliers, it's possible that someone sells a ready to buy kit but I tend to buy from Hoffman amps. As you said, I make a list of every cap value and buy them individually. It's also a good idea to use a current limiter/incandescent light bulb apparatus for cold starts after fresh work or long storage. That way, if the caps, or anything else has shorted you can see there's a problem before committing high tension to the circuit. Good luck!

[@rupe53]

@@FrankOlsonTwins Yes, have used the light bulb trick before I found that Variac at a garage sale and keep forgetting about the brightness of the bulb being a clue. Thanks for the reminder!

[@caseyholford]

Fascinating to watch you work. I can attest this amp sounds fantastic!

[@FrankOlsonTwins]

Thanks! Yes, 100% agree! I still might need to build the second "guitar" channel for my clone if I come across a slightly bigger chassis....

[@calescapee9642]

Now show em how to install a triode switch and turn the hum balance into a true bias control.

[@jackleg266]

the ground is not soldered, at all? great video. i subscribed....

[@FrankOlsonTwins]

Thanks! Correct, be sure it is crimped tightly and has no way of pulling out. I've read various arguments for soldering or not, but I believe the current standard is crimped without solder.

[@ertreri]

9:50 what is the principle of equivalence there for that one cap replaced by two caps?

[@FrankOlsonTwins]

That single original cap had 2 caps inside, tied together at the ground. It was a somewhat common space saving technique of the day. So, it's normal to just replace it with 2 caps of the same specs.

[@tjminasi1442]

You can get the dual 25uF caps from F&T, but they are size and cost prohibitive.

[@tomfoolery2082]

If the filter caps have been changed is there a way to tell how long the new ones have been in there ? Thk u much .

[@FrankOlsonTwins]

Not really- but you can make a guess by their size and possibly color. Caps have gotten smaller in recent years, so if they're from the 80's or 90's they'll be just a bit bigger. In the past, filter caps were different colors(like orange or blue) so that can tell you they are maybe from the 70's or 80's. Nowadays, they're pretty much all black or grey. I tend to look at it from a reliability stand point. In my experience, aluminum electrolytic caps(filter caps) generally last a minimum of 15 years. Anything above that is suspect(to me). I've done a lot of cap replacements on mid 90's guitar amps(grey Illinois caps), so that puts them failing around the 20+ year mark. OEM caps might last 20, 30, 40 years- especially if they are used often and are used below 250v. But it's a gamble. In those cases, with my own amps I'll continue to use them with older caps, but the very second I hear the slightest hum, the gets unplugged and tagged until I can replace the filter caps. The brand can also be a factor. Good brand caps almost always last longer- Original Mallory(A+) and Sprague had long lifespans and I have an amp or two still running with those original caps. As a rule, I wouldn't gig one of those amps without first updating those caps. So, to sum up: If your amp has "new-ish" caps and sounds good with no hum, you're probably fine for the near future, especially for a casual home or studio player. But if you want the most reliable amp you can have and peace of mind, just bite the bullet and get those caps changed- especially if it's a gigging or often used amp. Good luck!

[@tjminasi1442]

@@FrankOlsonTwinsYes, for stage gigging, change PS caps and leave the pyrotechnics to the professionals ! LOL

[@johnbravo7542]

You can't tell how long they've been in the power supply,but there may be a date code on the caps of time of manufacture.

[@cgavin1]

Great video. Why are you using 22uf not 25uf bypass caps?

[@FrankOlsonTwins]

I seem to recall my distributor only had the 22 sprague.

[@tjminasi1442]

22uF are common, 25uF Atom Sprague caps are about three times the cost and no better quality to Vishay/MOD and the like. The frequency response is equivalent to the ears.

[@scottwilcox6313]

Nice video, but WHY DRIL INTO THE CHASSIS. And crimped terminals?

[@FrankOlsonTwins]

Drilling a hole for a 3 prong plug is preferable to using a transformer lug, as was often done in the past. By getting it's own dedicated screw and nut, the odds of the ground lug coming loose is greatly diminished. Transformer bolts loosen over time and if the lug is attached there, there's a safety risk. Despite any potential value drop of a hole in the chassis, why risk it?

[@tjminasi1442]

Drill into a vintage amp. What are you thinking??!!!

[@JammyCrackcorn]

What doghouse Caps did you use..Where did you order them from?.

[@FrankOlsonTwins]

F&T brand, purchased from Hoffman amps

[@cardre]

Great detail and enjoyed watching the restoration. I've got a '73 Vibrasonic that needs this done as well. I've never done a tube amp before, but am comfortable working with HV and your video (and some others I've watched) have given me the reassurance I need as to what to do. Just got to work out where to get a cap kit for it (I'm in Australia) and which valves may need replacing. Hasn't been played for 20 years and only ever had 2 of the 4 main valves replaced, so I'm expecting to need to buy a few parts for it. I'm the second owner and had it for most of its life, so don't think its been messed with. I understand internally its basically the same amp head as the Twin, just got a single 15" speaker instead of the 2 x 12". Do you normally get a kit of replacement parts, or individually order just as you need?

[@FrankOlsonTwins]

Thanks for checking out the vid! Is your Vibrasonic amp basically working? Is it showing symptoms of needing caps? Here in the states, I usually buy amp parts from hoffman amps .com, but I sometimes get parts from mouser .com If Hoffman will ship parts to Australia, he's got everything you need, and you can email him for advice on specific parts as well. Buy all the parts for a Resistive shunt wire, and make that first! You can also tape one end to a chopstick which will keep your hands clear of the internals of the amp until it's discharged. F&T are the current best value for quality, large filter caps. I generally try to steer clear of sprague, simply because they are SO expensive now. For a fender amp like this, however, I usually opt for the sprague bypass caps(electrolytic, that is). I bought a few cap kits from a place called studio parts(?) once, it was fine for smaller amps as I recall. Ebay or Reverb might also have some sellers that will sell you a cap kit. But try Hoffman first. Good luck, and remember- Safety first! 😉

[@cardre]

@@FrankOlsonTwins Thanks for that info, I'll check them out and see if they'll ship to Australia. I do normally get stuff from Mouser for my digital projects, but didn't know if they sell some of the bits for older tube amps. Last time I used the amp, it was working, but definitely had some hum, so I suspect something was on its way out. Previously when 2 of the main tubes died, it was like an arc welder was going off in the back of the amp! Was scary to reach around and turn it off. After replacing 2 of the 4 main tubes though, came good again, but still that hum. As its been so long ago though, I'm a bit worried to just turn it on and think I should do the electrolytics before trying as I don't want to damage the rest of the amp. I have seen some videos where they use an autotransformer(?) to slowly ramp up the AC (240V here in Australia) to try and reform caps, but I don't know if I should bother. Yes, will definitely make that Resistive shunt though first, what ohm and power rating did you use/suggest? Chopstick is also a good idea! It has been unpowered for a long time though, but if I need to power it on at different stages, will want to do that discharge process again.

[@FrankOlsonTwins]

For a shunt resistor, I use a 5K, 5 watt ceramic resistor. But anything between 1K and 50K, 3 watts and up is fine. It's a balance between drain speed and keeping the capacitor healthy. Draining too quickly will damage the cap. Too slowly and you'll be waiting forever to work. Many tube amps have a drain resistor already installed. The bassman in the video you can see a 22k resistor between the first cap and ground. That resistor should drain the amp efficiently in the first 3 minutes, but if it ever fails, you'll have a live chassis on your hands. That's why it's best to drain with a resistive shunt, then check the voltage with a meter as a matter of good practice. Mouser carries a lot of parts that can be used for these amps, but the tricky part is finding the exact one on their website. Yeah, it sounds like your filter caps are on their way out. Also, a few of the same resistors on the power tubes are probably fried. I wouldn't bother trying to re-form the caps. Sometimes that works, sometimes it doesn't. To me, it's a temporary solution. I'd rather just replace the caps and not worry about it. If you're worried your caps have completely died, you can make a "Lightbulb Limiter" which is easy to do with just a handful of parts. Look up "lighbulb limiter" for plenty of schematics. Basically, you run a lightbulb in series with the mains of your amp, and if the lighbulb glows very brightly, you've got trouble in the power supply(such as a shorted capacitor or power transformer). But if the lightbulb just idles, you're okay to power up normally. You should only use old school incandescent bulbs, no eco bulbs or flourescents, they won't work. Gook luck!

[@cardre]

@@FrankOlsonTwins Thanks again for this great feedback and info. I've seen those "Lightbulb limiter" projects being used for other vintage electronics and will definitely include that as part of getting setup for the restoration. You're most likely right about needing to replace some of the bias resistors on the tube sockets, so they'll be carefully checked as well. I guess the final piece of the puzzle will be in working out how to determine if a tube is ok, or should be replaced, besides the obvious of the amp works or not. I know in the case of failure there is generally something visible to see on the tube, but if a tube is somewhere between passable and good is another matter. I guess carefully using my scope to monitor voltages in/out etc while injecting a signal, but that's also dependent on the tube and its purpose in the circuit, not to mention safety issues. I've seen a YT channel mention that if you hear/detect a 50/60Hz hum (depending on your electric supply) or a 100/120Hz hum, it can indicate a failing tube or a failing cap, as one frequency is likely the tube and the other is likely a cap. This would need careful tracing to determine which one I'm guessing. Do most people just replace all the tubes in a vintage restoration, or just try to identify the ones that are failing/failed?

[@FrankOlsonTwins]

Generally speaking, people(and techs) often just replace power tubes all at once. The remaining good ones can be used as spares or amp testing in the future. Preamp tubes are usually replaced as needed, since they can last for many years, even under heavy workloads. To check preamp tubes for failure(or just bad sound) make a not of what section you thing sounds bad(ch. 2 for example) and move the suspect tube into different positions. The idea is that the bad sound will follow the tube. If, after moving a tube to the first preamp position(usually v1), channel 1 suddenly starts sounding bad, you now have a good idea which tube is bad. You can do the same thing with power tubes, to an extent. Temporarily put a new power tube into each position and listen to hear when it gets better. It might be worth pickup up an old tube public address unit or cheap champ type amp to work on to get your skills sharpened before opening up the big fender. I suspect you'll find many "Aha" moments in a small restoration that will apply directly to the big amp. Also, it's nice to have a working smaller amp to test out tubes on, to hear which ones sound good or are ready for the bin.

[@yoshiyaz5882]

👍😃

[@FrankOlsonTwins]

🙏🙏

[@5barkerstreet]

Lol