1965 Fender Vibro Champ Amp.....Beautiful Condition but Smokin' Hot !!

This video features an exceptionally nice, completely original 1965 Pre-CBS Blackface Fender Vibro Champ Amp with a problem that is not unusual in amps of this vintage: Extreme Overheating. The diagnostic process is presented, step by step, and the problem is resolved in the least obtrusive manner. In addition, Rusty makes three appearances on screen (and countless contributions behind the scenes) that will thrill and delight his many fans ^. .^
If you enjoy videos featuring classic vintage amps, jukeboxes, home-built electromechanical marvels, and clear, concise technical presentations, then please subscribe to my channel. You will receive immediate access to almost 100 additional videos, and (if you activate the service) you will be alerted each time a new video is posted.
Rusty adds: Thanks for watching !!!

[@Classix1969]

isn't it awesome to see such a pristine handwired amp, just beautiful

[@UncleDoug]

Thanks.....glad you like it :)

[@tmitz73]

Love me the sound of a nice Vibro - Champ!! Thanks Uncle D, stay well, healthy and happy!! Rusty is sooooo Ruling!!

[@UncleDoug]

Thanks, T. You too :)

[@jdb2722]

Good job Rusty! I have an 81 and it’s in excellent shape. Love it. My favorite home practice amp.

[@UncleDoug]

Thanks, JB :)

[@SasquaPlatypus]

GET 'IM RUSTY!! Great looking amp, love your channel, I've consulted several times for some good troubleshooting. Thanks Doug and Rusty!

[@UncleDoug]

You're welcome, SP. We really appreciate your nice comments :)

[@jadefire1985]

Good to have you back uncle Learn so much and you have such a charming manner.If you'd been a teacher in my school I'd be an astronaut by now

[@UncleDoug]

It's good to be back, JF. Thanks for your kind comments. By coincidence, one of my ex-students (Science and Math in grades 4-8) really is an aerospace engineer.....so you might be right :)))

[@rbauer1632]

Hey Doug. Just wanted to thank you for sharing your expertise with us less knowledgeable, but no less interested DIY amp techs. Followed your discussion with Aaron Bean, and there was a lot of knowledge gained.

[@UncleDoug]

You're quite welcome, RB. I'm glad the videos and commentary have been helpful. Thanks for your kind words :)

[@picker63028]

Doug, I enjoy your video's and appreciate the detailed explanation. As an old Fender fan, I have quite a collection and have repaired several. I use the information from you and the library of books I read. Anyway, many thanks.

[@UncleDoug]

picker63028 You're welcome, Picker. Rusty and I are glad our videos are helpful. Best of luck :)

[@Jackmc2112]

I was born June 65’. Wonderful video. Send me back to 1985 Great Lakes NTC where I learned electronics.

[@UncleDoug]

We're glad the video brought back good memories, Jack.

[@brentatkinson73401]

An amazing amp and a very educational and extremely well done video and good job Rusty 🏆

[@UncleDoug]

Thanks so much, Brent :)

[@rebelrelicguitars]

Very helpful. I have precisely the same problem with a 1976 Vibro Champ. Ordering the necessary parts now. Thanks Uncle Doug!

[@UncleDoug]

You're welcome, RRG. Good luck.

[@rodneykroetsch2924]

Thanks so much, for your way of sharing knowledge and making it understandable...your the best!

[@UncleDoug]

You're welcome, Rodney :)

[@user-ux1bm2br7u]

G'day there, Glad I discovered your channel. My comments are 10 years too late ... but ... while your changing of the 6V6 cathode resistor from 470 to 800 ohms is perfectly correct to reduce the plate dissipation, it is the fact that the VC circuit is running too hot (even on a brand new VC from the late 60s and 70s) that gives the amp its distinctive sound. Fender's initial B+ was 355V on the AA764 circuit in the early 60s but raised it to 420V on the late 60s and 70s models using the AB764 circuit. Changing the cathode resistor as you have done gelds the amp ... so to speak. The valves from the 60s and 70s can handle, and obviously did handle, higher plate dissipation than one may normally design for. It is the sound of the 6V6 working hard that guitarists love. Raising the 6V6 cathode resistor to around 800ohms removes this OD sound from the amp. In the builds I have done (and where I have had to repair a DOA vintage VC) using a 10W 470ohm cement 6V6 cathode resistor, adding in suitably sized screen and grid stoppers to the 6V6 keeps the great OD sound of the VC and ensures it doesn't overheat or burn out the cathode resistor (which often occurred in 70s VCs). Using a vintage NOS or ANOS 6V6GT power valve (a single vintage valve is relatively cheap and will outlast any Chinese or russian built 6V6) makes the amp safe and still sounding awesome.

[@UncleDoug]

Thanks for your helpful input.

[@amoruzz]

Gold Bond stamps.. wow Always something special in your videos. Thanks!

[@UncleDoug]

I recall many a happy day as a callow youth, helping my mother lick and stick S & H Green Stamps in booklets, in anticipation of an exciting trip to the redemption center.

[@mudylafeet]

Nice of Rusty to explain all this to you and to us all, thanks again, great video!!! :)

[@UncleDoug]

Hey, Mudy....It's good to hear from you. Yes, I would indeed be lost without Rusty's leadership and guidance. He is a very helpful hound :)) ^. .^

[@mudylafeet]

Uncle Doug Hilarious U Doug, btw i continue to share youre awesome videos on my FB group of guitarists, makes quite a stir, please let Rusty know and yall keep up the fantastic work, cheers to both !!! :)

[@UncleDoug]

Thanks so much, Mudy......as long as their are appreciative viewers out there like you, Rusty and I will be churning out the best (beast) videos we can :))

[@Dan79istheman]

Thanks Uncle Doug, I really was experiencing "Uncle Doug Video" withdrawal symptoms. No joke, my wife did not know how to help me. But alas, I feel much better now. I have also completed my very own Fender style amp with a pair of 6V6GT's in the ouput, using your video's as a guide. Stay groovy Uncle Doug.

[@UncleDoug]

I'm flattered that you missed me....and it's good to be back, Dan. I took a few weeks off to work on other projects, but couldn't resist getting back on KZbin with another video :) Congratulations on completing your Fender-style amp !!

[@mudylafeet]

Uncle Doug and Rusty, the kindest electronic tube tech-teachers on youtube, you guys Rock!!! Cheers!!!

[@UncleDoug]

Thanks, Mudy. Rusty and I are getting old.....and most of our rocking is in a chair......but we still appreciate nice comments from great viewers like you :)

[@mudylafeet]

Uncle Doug Old Whiskey is the Best, yall keep pumping them videos, any chance on a high powered Marshall a/b amp sometime? BTW put some rubber on them rockers so u dont wake anybody while Rockin, yall fantastic, so glad i found yer channel, G Bless you both !!!

[@UncleDoug]

Mudy, there just aren't any vintage Marshall amps in my area....and I don't work on modern (printed circuit board) equipment. Maybe one day, one will show up at the workshop door and Rusty and I can feature it in a video. We'll keep our paws crossed :)

[@moodyga40]

love it uncle Doug missy boo is starting to building a amp

[@dtotheatothevtothee]

Excellent video, sir!

[@UncleDoug]

Thanks, Dave. Glad you liked it!

[@conjering]

Doug I really like this video, very educational. I can't wait to see you work on a old Marshall Amp and give us an orientation on it.

[@UncleDoug]

Greetings, CJ, and thanks for your kind comments. I only work on vintage tube amps, and very rarely, if ever, get my hands on an old Marshall or Vox amp. There are lots of modern ones floating about, but virtually no old ones at all. If that situation changes, I will gladly post a video orientation, as you requested.

[@kcole-xi9km]

What a really sweet looking amp! My friend had a Vibrolux he bought from a lovely old girl who had used it for violin, she had bought it new and it was absolutely pristine, just a little corrosion in a couple of jacks on the back panel. It sounded amazing, and it really loved his '64 Jaguar or his Strat, didn't work well with his Les Paul, however. I used to have a blackface Bassman head that would get pretty hot, you could touch the stand by switch, but you wouldn't want to hold on to it. I just thought that was normal...it was pre internet days, no one around here knew any better. I still miss the smell of a hot tube amp, probably the scent of baking tolex, but still, it's a strong memory of my earlier days: leaning over the top of it to flip the standby switch. it wasn't much of a bass amp, particularly for a Rickenbacker, lacking a mid control, but it was a killer guitar amp. I really should have kept it. Anyway, love the videos, they almost make me think I could build one of your projects, but without any proper electronics background I think it's better I don't. Say hello to Jack for me! He's an important part of the operation. :)

[@UncleDoug]

Thanks for your very nice note, KC. Keep watching and learning.....and you'll be building amps some day ;)

[@LeonelMendrix]

You're amazing Uncle Doug :-) it's a honor to watch your videos and learn something... and your dog are the one ;-)

[@UncleDoug]

+Leonel Mendrix Thanks so much, Leonel. Rusty and I really appreciate it :)

[@LeonelMendrix]

+Uncle Doug I think Rusty want that Vibro Champ just like me ;-) you should let him play guitar sometimes ;-) Greetings from Portugal.

[@UncleDoug]

Actually, Rusty did get to play a Chuck Berry tune in one of my videos. Keep watching and you will find it :)

[@corralesdavid]

Great to see more videos, thanks as always! Rusty is killer as well :)

[@UncleDoug]

You're welcome, David; and, speaking for both me and for Rusty (who is busy at the moment sniffing the neighbor's poodle) thanks for watching and for leaving nice comments :) ^. .^

[@s2arto]

Doug, really enjoyed this video. My '65 VChamp also runs plate voltage in excess of 400v. Now I have a remedy for getting plate dissipation closer to normal.

[@UncleDoug]

Greetings, S2. I'm glad the video was helpful. Yes, indeed, some of these old Fender amps tend to be biased way too hot. Thanks heavens a simple increase in bias resistance can lower the PC and PD to reasonable levels. Best of luck taming your '65 Champ :)

[@alvagoldbook2]

I was most surprised by those stamps! Many years before I was born, my mother worked in a stamp store!

[@UncleDoug]

I used to help my mother paste Green Stamps into booklets when I was a kid. Then we'd go to the nearest redemption center and get stuff like TV trays, toasters, etc. It was like Christmas.

[@88merc300e]

After you asked Rusty if he was excited about the amp he winked at you ;)

[@UncleDoug]

That's his secret code for "give me a steak bone or I'll bark a lot and ruin the video"....... :)

[@88merc300e]

Uncle Doug Oh I see lol.

[@LowEndStrings]

great video. love how detailed you explain everything! :)

[@UncleDoug]

Thanks, LES. I have a bunch of other videos posted that may also be of interest. Please check them out when you get a chance :))

[@LowEndStrings]

i gues I've seen all the videos that you uploaded! :) by the way, did you get my messages, that i've sent you via youtube a few weeks ago? cheers :)

[@UncleDoug]

For some reason, I am not notified when YT messages are received, so I tend to miss them. You can send messages to my Facebook page: Uncle Doug's Vintage Amps and I will receive them.

[@iyup2964]

Thank You! Nice video.

[@UncleDoug]

You're welcome :)

[@captainfineweather5610]

RUSTY RULES !

[@UncleDoug]

Yes, indeed :) Thanks, Capt.

[@bullthrush]

Great looking amp! Rusty was playing it cool to offset the heat from the amp. :))

[@UncleDoug]

Thanks, BT. I guess some dogs can sense earthquakes and others are sensitive to abnormally high plate dissipation :))

[@1980bwc]

Rusty's wink was perfectly timed.

[@UncleDoug]

He was a skilled actor :)

[@gringopig]

Great info Doug!

[@UncleDoug]

Thanks, GP :)

[@BourneAccident]

Rusty, I opened up one of those MADE IN CHINA tubes. There's a spring, an elastic, some used bubble gum, bits of old dog bones, and some green stuff that glows in the dark. With that being said, I think it was a good thing that your Uncle Doug replaced that tube. That's about as technical as I can get with regard to my expert analysis. Enjoyed the video very much.

[@UncleDoug]

Thanks for the detailed analysis, BA. Rusty got excited about the "old dog bones" and started chewing on some Chinese tubes :)

[@cgavin1]

I was just going to comment this lol. If its painted black its because they don't want you to see whats inside hehe.

[@johnmac8084]

That's a beautiful example Doug. I rarely see a Blackface Vibro Champ in the UK, in any condition, never mind pristine. Thanks for sharing.

[@UncleDoug]

Thanks, John. We're glad you enjoyed it :)

[@tremelo68]

Great, thorough explanation! Part of the high Pv might be attributed to our higher home voltage compared to the 110 of the 60s.

[@UncleDoug]

Thanks, Trem. You're right....my wall voltage runs about 10% higher than the original 110VAC, so it's to be expected that the B+ values will be about this much higher than it was in the original circuit and schematic.

[@twirlyboggs]

cool vid! I like how you wanted to preserve the magic of a vintage amp instead of just replacing all the components on the board -

[@UncleDoug]

Greetings, TB. Yes, I try to be as unobtrusive as possible when repairing these nicely preserved old vintage amps, generally using vintage-style carbon resistors and only changing what must be changed to make them work well. In this case, the owner requested this conservative approach.

[@rodneykroetsch2924]

Uncle Doug, i have a 1966 Vibro Champ on the bench. While not as cosmeticly clean as this...every bit as original. Original CRA 5Y3,6V6 and 2 Telefunkin 12AX7,s. Same problem. Running way hot. Blown speaker. I opted for the Weber Sig 8 alnico. I had to replace a few out of tolerance res. Ended up using a 811 ohm cathode res. To bring me to 30.5ma draw with the original CRA. SOUNDS SO SWEET....i don't want to give it back. The Weber is a great speaker in these amps!

[@UncleDoug]

Greetings, Rodney. Yes, indeed, many of these old BF Fenders are biased waaaaaay too hot. Hopefully, viewers will see comments like yours and mine, and check their bias before damage occurs. Also, as you say, if they need a good replacement speaker, Weber definitely makes them. Thanks for your input.

[@UGotMalk]

you are really great at fixing things !!! I wish I had your knowledge..lol

[@UncleDoug]

Thanks, UGM. Anyone can do it; it just takes some study and the willingness to apply yourself to the mastery of a skill. Much like learning to play the guitar. At first it may seem hopeless.....but you keep at it until you become proficient.

[@montygore]

Hi Uncle. I can still taste the blue on the back of the green stamps.

[@UncleDoug]

Yeah, my tongue felt like it was dipped in toxic waste......until we discovered a moist sponge ;)

[@itsstillfriday]

I LOVE that Rusty-Dawg!! :)

[@UncleDoug]

Me too. He was once an unknown pup, but is now an internationally-known actor and videographer with an agent and an entourage of poodle groupies :)

[@josesaldivar655]

Greetings to Rusty too

[@mickizzo]

It’s important to remind everyone that these amps were designed to run on 110-115 vac, not the typical 120-123 vac we have today. This usually accounts for vintage 6v6 amps to run hotter than designed. It’s also important to note that while increasing the value of the cathode resistor may drop the tube wattage to an acceptable level, doing so can make the amp sound dull and lifeless. Chinese firecracker tube aside, I bet if you ran this amp through a variac at 110 vac you’d find it running within spec as designed. BTW I really enjoy your videos. Keep up the good work!

[@UncleDoug]

According to the original Fender schematic, the VC operated at a PV of around 420VDC, which is 105V higher than the tube manual max. If the PC was a typical 35mA, this would result in a plate dissipation of 14.7W, which is 22.5% above the max PD for a 6V6. So, there is no doubt that the amps were biased very "hot" from the factory. If the input AC is elevated 9%, from 110VAC to 120VAC, you can see that PV and PD would increase to an even more outrageous level. For this reason, it is imperative that viewers measure and determine the PV, PC, and PD of their Fender amps, and reduce the PD to an acceptable level. I disagree that doing so will degrade the tone......in fact, I think you'll find that it is actually improved a bit, and your tube life will be extended dramatically.

[@rcgillsympaticoca]

Really enjoyed this vid. I guess this question and reply mostly answered my question, but was there a single component that drifted out of spec to cause this or was it just the original factory setting of this amp coupled with the more modern AC input voltage... oh, I guess the Chinese tube played a role also. Would be nice to know what was going on inside there since it tested ok on its own. Very interesting. Thank-you!

[@UncleDoug]

@@rcgillsympaticoca It was a combination of all the things you mentioned, Rob, and it's a common problem that should be addressed by all owners of vintage Fender amps.

[@holmes1978]

So Fascinating !!!

[@UncleDoug]

Glad you liked it, LH :)

[@latouselatrec]

I'm so sorry to hear of rusty's passing. Ouch

[@UncleDoug]

Thanks, Marco.

[@boboala1]

Hi Doug! Love all your videos! My first experience with electric guitar & amp was around 1975 (ahh...Sophomore year in HS - rewind, please!) with a friend's Fender Vibrolux Reverb amp. Ever heard of it? It's extinct like I am. BTW, Rusty reminds me of my elderly cat Weezee...both of which are what I lovingly think of asl a 'Furry Turder' ;)

[@UncleDoug]

Greetings, Bob. Yes, I've heard of it and even posted a 3-video series on the Fender Vibrolux. Here is a link to Part 1: kzbin.info/www/bejne/qJvVk4eQj96Vd8U Rusty sends his regards to Weezee.

[@BurnleyNuts]

Just love your videos Uncle Doug and full respect as a teacher of electronics you really are great and I've relearned so much stuff from my classroom days. You really do remind me of my old RAF college tutor whilst I was an apprentice in the early 80's. However before we get all xenophobic over American and Russian and Chinese valves, I should point out that at 7.09mins into the video and around there it's really clear to see that the Chinese tube has a crack in the glass thus the vacuum will be lost. As I also learned as a young engineer back then the saying 90% observation, 10% perspiration.

[@UncleDoug]

Thanks so much, BN. The tube you mentioned did not have a cracked glass envelope......the inside surface had what appeared to be a long, thin scratch in the inner coating that gave that impression.

[@jimraimondi410]

This video helped greatly. I have a '76 Fender PA100 with PC reading @ 30ma at its lowest setting and PV @ 699V.

[@UncleDoug]

Jim, since the PA100 has two pairs of 6L6's in parallel, I wonder if your readings may not be for a pair of 6L6's, i.e. they are doubled. This would make the PV = 350VDC (much more believable) and the PC a very low 15mA. You need to check the schematic to be sure.

[@TerryMcKean]

02:09 I remember "S&H Green Stamps" and "Blue Chip Stamps" when I was little. :-)

[@UncleDoug]

I licked Green Stamps for my mother, until my tongue got sore.

[@joeflaherty936]

These videos fascinate me. Some people must be electronic geniuses to understand all of the nomenclature, but I still love this stuff.

[@UncleDoug]

Greetings, Joe. I'm glad you enjoy the videos :)

[@joeflaherty936]

Uncle Doug You're very welcome, Doug. I'm just glad there is somebody who has taken the time to upload these videos. I can't get enough of 'em.

[@joshdelafuente1171]

You are an expert. I'd like to bring my stuff to you to work on!! Great video

[@UncleDoug]

Thanks for your kind words, Josh :)

[@lgmnowkondo938]

first things first...you make very good videos. I don't know how old you are...but watching your vids reminds me of spending time with my grandfather in his shop while he would explain similar things to me. Now...how come we didn't get to hear this amp before and after??

[@UncleDoug]

Thanks, IK. I was born in the late 40's, so I'm probably old enough to be your grandfather :) The amp sounded about the same before and after. I intended to video the owner testing it when he picked it up, since he is a good guitarist, but he was in a hurry and the test consisted of a few notes, verification of the reduced operating temperature.....and out the door.

[@Tonetwisters]

I SO wish Fender would have (or STILL WOULD) make a 20-25 watt amp that sounds like these Class A amps do! And none of the custom amp builders seem to have a clue ... These are just very unique and very warm sounding amplifiers and I super love their tone! Best way to fix this amp is to dump a tray of ice on the top and let that cool do its job! Right? Amazed that these little amps put out nearly 13 watts! Double that amp in a 2X10 cabinet, and what a sound you would have! Nice to revisit Rusty. Rusty In Peace ...

[@UncleDoug]

The problem is that it's really hard to emulate the warm Class A tone of a single-ended circuit with a Class AB double-ended, more powerful, circuit. Perhaps a SE circuit could be built around a KT-150 tube ?

[@dorianmichael4360]

i'm old too, waaaa. i remember doing the stamp thing with my mother. i think we had "green stamps". i also remember when the tv stations went off the air at midnight and put up the test pattern.

[@UncleDoug]

Fond memories that I too recall, Dorian......and the test pattern always had an Indian chief in the center. This, I never understood.....what is the relevance ?

[@daveogarf]

GOLD BOND STAMPS (and S&H Green Stamps!) Right there with you, Uncle Doug! I clearly remember the cashier dialing up the amount on the stamp dispenser - and the Redemption Book, FULL of excellent teases in the form of supplies and even toys! SIGH!

[@UncleDoug]

Those were the days, Dave. I would help stick the stamps in books and then ride with my mother to the redemption store to pick out merch for the house.

[@leewar40]

Rusty for President!

[@UncleDoug]

Thanks, Warren :)

[@crazybaldheadz]

Thanks for this great video Uncle Doug! I adjusted my 77 Vibro Champ down from 19 watts to 12. She's never sounded better!

[@UncleDoug]

+crazybaldheadz You're welcome, CB. I'll bet your 6V6 is happy that the thermostat has been turned down.....it must have been roasting :)

[@BrickwallJackson]

Best dadgum channel on KZbin!!

[@UncleDoug]

Wow.....high praise indeed. Thanks, BJ :)

[@donrutter6765]

My 68' super reverb came with that exact chinese black tube, but for a GZ34 Rectifier.

[@pedenphoto]

Uncle Doug, Peden In NYC here again. Great video as always. I'm going to contact Rusty's agent to see if he's interested in a part (non speaking) in an upcoming video I'll be producing . In reference to the blackface amps having high plate voltages. Leo was pushing the envelope in those days when 110 volts was the standard A C. Here in the big city in 2018 our wall current is much higher so I use a buck transformer device which lets me attach a plug strip that delivers 110 to at least an amp and reverb unit. If you have several amps this method saves the problem without having to modify each amp. You've probably covered this in another one of your excellent videos but I thought I'd ask. BTW 2 items I've worked on that might interest you are : a You Tube video where guitarist G.E. Smith examines and discusses Mike Bloomfield's Telecaster (You Tube>Bloomfield Telecaster) and a book on Fender amps "The Soul of Tone" author Tom Wheeler. Check them out you might enjoy them. Tell Rusty we'll pay his travel expenses when he comes East.

[@UncleDoug]

I'm sorry to report that Rusty has passed away, Peden. Thanks for the tips. I will check them out.

[@gRosh08]

Sweet! Rusty is ready to go fishing!

[@UncleDoug]

Thanks, GR :)

[@gRosh08]

@@UncleDoug Rusty is such a great friend! I love the stuff you work on and my dog Bentley, is so much like the younger Rusty I can't stand it! Well done!

[@UncleDoug]

Thanks again, GR. I hate to mention it, but Rusty passed away several years ago. He lives on, however, in our earlier videos :)

[@gRosh08]

@@UncleDoug I am so sorry.

[@frankymcdonald3081]

I guess Rustys to "Hollywood" to play us a solo. but i can understand if hes preparing for the Oscars. Great video Uncle Doug.

[@UncleDoug]

Thanks, Franky. Yes, Rusty is currently at the Rock & Roll Hall of Fame, where he is posing for a bronze statue of him doing the "Duck Walk" with a mint 1953 Telecaster. I also understand that Chuck Berry asked him for an autograph :)) ^. .^

[@dylancole2946]

Dropped in a 820 ohm that metered closer to 970. I get a drop now of 33 volts which gives me about 14 watts disipation. High for an old tube but the JJ data sheet I found has 14 watts at the top end. I'm trying to find a silverface schematic as I've read the voltages changed on the schematic at some point to the 400+ range I'm seeing under the hood. This has been a great series of videos! I've learned a ton. And tubes are way easier to work with than mosfets and transistors - I don't get hand cramps trying to manipulated those tiny Lil legs or eye strain trying to count pins on tiny chips.

[@UncleDoug]

Dylan Cole That sounds a lot better, Dylan, but 12W is the more common max PD value. Although the PV seems high, this is typical for BF and SF Fender amps. The PC of 34mA still seems a wee bit high to me, but if it sounds good and you're happy, then so be it. Congratulations on a successful biasing procedure. I'm glad the videos were helpful.

[@davidjennings9253]

Hi Doug. I loved this video, as I own an absolute mint 65 Vibro Champ and it is totally original. The only fault I have had was a poor solder joint on the ground tag of the input 12AX7. Apart from that the amp sounds wonderful in every way. I have learnt so much from your channel that I feel comfortable that I can keep it that way in the future. Have you got a video on servicing a Vox AC30??

[@UncleDoug]

That's great to hear, David. So glad the videos have been helpful. No, I have never received a Vox AC30 for repairs.

[@jimraimondi410]

That makes sense. When I first checked the bias it was set at 65ma which would really be 22.5ma or so.....I will check schematic to make sure. Thank You very much.

[@UncleDoug]

Jim, if it was 65mA, then it would be 32.5mA for each 6L6. Depending on your method of measurement, the PC and PV can be doubled with parallel pairs of output tubes (which you have). Also, different types of 6L6 have very different PD maximums. American GB's @ 19W; Russian GB's and 5881 @ 23W; GC's @ 30W.

[@bluebuddha6663]

I really enjoy your videos, they are very informative and entertaining. I think you made a small error in calculating plate dissipation though. With cathode bias the voltage drop across the cathode resistor should be subtracted from the plate to ground voltage before calculating Pd.

[@UncleDoug]

BlueBuddha666 You make a good point, BB. This is why I included notes in the video suggesting that the PV be measured from plate to cathode, rather than from plate to ground. The plate to ground method results in a slightly "cooler" bias, which is probably best for beginners (why I did it this way in the video), but is not as accurate as plate to cathode.

[@counciousstream]

I have what I have now identified as a 1966 Fender Champ using the rubber stamped date codes on the tube diagram located inside of the cabinet. It indicates that it was assembled in October of 1966. I just took it apart and it looks identical to the amp in your video with the exception of a Fender logo on the speaker fabric and without the Vibro lettering on the front. Although it is clearly after the CBS acquisition it does have the same control knobs with set screws at the 10 mark. The back panel says Fender Musical Instruments and doesn't include the CBS Musical Instruments lettering on some older amps. I was having a problem with the volume cutting down significantly after about 10 mins of playing. The pots were scratchy as well so I gave each a shot of crc contact cleaner and then took each of the tubes out and gave both the receptacles and tube contacts a cleaning as well. After re-assembling it now sounds great and there is no volume cut back like before. I guess that a little TLC was all that was needed at this point.

[@UncleDoug]

It sounds like a great amp, Bill. Progressive loss of volume can result from failing coupling caps......so keep an eye (and ear) out if it starts happening again. Good luck.

[@ipguyman108]

Thanks Rusty..!

[@UncleDoug]

ip man You're welcome, ip ^. .^

[@ipguyman108]

I know you mentioned that you don't repair out of state. But I had my old supro repaired 3 times in this area but it just fdied out. Can I send it to you? Russ Cichon

[@UncleDoug]

Russ, I would love to help, but I really have retired from doing outside work....especially if it involves shipping. Hopefully, you can find someone else in your area to take a look at the amp. Good luck :)

[@ipguyman108]

Thanks so much Uncle Doug. That's ok. I realy enjoy your videos anyways. I hope you and Rusty are doing well. P.S. - my uncles used to nick name me "Rusty" also. ha, ha..

[@UncleDoug]

You're welcome, ip. We hope you can get your amp repaired.....best of luck.

[@jorgemellooliveira9611]

Sonho de todos guitarrista um amplificador lindo leve para transportar ótimo vídeo mestre Jorge Sul do Brasil

[@UncleDoug]

Thanks so much, Jorge. Glad you enjoyed it :)

[@scootertrasher1369]

thanks for another great video, ( I know it's three years old ) but not out of date, I would think nearly all vintage amps from the sixties back if unaltered are running higher than spec voltages,causing bias to be off, due to wall voltages morphing from 110v to 115v to 120v up to even 125v at times. Especially Fenders that seem have started the trend of pushing the envelope on voltage !

[@UncleDoug]

You're welcome. Yes, the increased wall voltage does increase the voltages within an amp.....but with proper biasing, it's not much of an issue. If one is concerned, they can use a current limiter to reduce the voltage to original 115VAC levels.

[@catdumpling]

Glad to see a new video! I haven't seen too many issues with Chinese (Shuguang) tubes, at least between friends and myself. But they've always been your standard clear glass bottles, nothing that looks like that. That's a weird one and I have to wonder if there was a reason they blacked out the glass? Maybe it was cheaper than, y'know, doing quality control.

[@UncleDoug]

Greetings, Cat. It's good to hear from you. I trust that the Magnatone Melodier project is going well. Re the mysterious tube, I have never seen anything like it either. It's almost like it was really a 6L6GC or some other current hog, but in a glass bottle labeled 6V6. The tube is gone (with its owner), so I guess we'll never know for sure.

[@catdumpling]

I'm almost ready to get back on track with the Melodier. I've just about finished my Strat project: got a nice NFT Floyd from Freddy Gabersek (used but nearly perfect), I'm still in love with the Bill Lawrence pickup and the only thing I have left to get is a set of locking tuners. Unfortunately I did have to replace the neck (factory one was twisted), but put on a MightyMite and I like it far more than the original in all respects, so it worked out. As with many projects, it ended up costing me more than I thought it would, but oh well. I've had a great track record with necks in my 26 years of playing, so I guess it was about time I got a bum one. Of course I didn't really notice it until _after_ the return period, but such is life. The guitar plays great though and is exactly what I was shooting for! Now that the guitar is about 98% done, I'm getting back into amp-building mode. I'm leisurely re-reading some things, just to remind myself of all the stuff I've forgotten. Luckily I kept a ton of notes, so it'll be easy to pick up right where I left off (and my TDPRI thread was great for that too.) Starting to think about the cab situation. Found some good raw cab builders with affordable prices, but I'm keeping my eyes peeled for a piece of vintage furniture I might be able to repurpose too: maybe an old radio with broken guts, or a small nightstand/drawer thingy like my grandmother used to have. Perhaps a small wooden footlocker-type-thing. The garage sales should start cropping up soon too, so I'll have to poke around the neighborhood once the signs start showing up in the middle of the night. I made a mental deal with myself that I'm not allowed to start anymore projects until I finish the amp...so we'll see how long it takes my brain to start arguing with itself. ;)

[@UncleDoug]

I'm glad to hear that the Melodier project is back on track. Re an interesting cabinet, I occasionally see small, arched-top trunks.....like pirate's treasure chests.....in antique stores (and Hobby Lobby). The arched lid would provide clearance and good protection for the tubes when closed, and you could open the lid for visibility (and heat venting) when the amp was in use. Majestic made a radio (Model 381) in this style back in the early 1930's that was quite snazzy. Regardless, best of luck with all your projects :)))

[@raymondheath7668]

Always love the math!

[@UncleDoug]

It's God's language, Raymond :)

[@billmckenna7056]

Nice fix Doug, Seems like all the old BF fenders run hot as you mention. Leo probably had higher expectations those days of what the tubes could take :)

[@UncleDoug]

Yes, they did tend to bias the vintage Fender amps a bit on the toasty side, Bill. Back then, you could buy new tubes at the local hardware store for a dollar (or less), but now it can be a rather expensive mistake. I recommend that all old Fenders get their plate dissipation checked and adjusted.

[@silasfatchett5693]

Line voltage having risen since these amps were designed probably doesn't help

[@audiosaurus6511]

Rusty likes them cold ;)

[@UncleDoug]

Actually, the smell of roasted Tolex seems to enhance his appetite. I guess it reminds him of some of the table scraps we give him :)))

[@moodyga40]

love the American tubes

[@djfrank59]

This amp looks like it's in great condition (well kept) I recently serviced one which had the same issue, except the 6V6 was red-plating beyond its limit and had a melt-down, which created another disaster...a fried power transformer. It was another situation where the owner had replaced the original tube which was functioning perfectly) with a Chinese 6V6 (clear glass). He felt that the original was aging and he could obtain better output and tone with a new tube. however, it came back to bite him in the keester! I tried to explain to him that just because a tube is old, doesn't mean it's not good anymore. the emission in the original tube was excellent with no sign of leakage or shorts. The clincher that killed the transformer is when the plate in the Chinese tube melted. it was to my discovery that the 1 amp slo-blo fuse was replaced with a 3 amp slo-blo. I replaced the power transformer, filter cap, cathode resistor, and soldered in a pig tail fuse under the chassis to kid-proof it. Another great video as always...especially with rusty as the director! :)

[@UncleDoug]

Thanks, Frank. Most people know better than to poke around in an amp chassis, but changing tubes is something just about everyone feels comfortable doing on their own; therefore, they tend to opt for that route whenever an amp doesn't sound quite right.....or if the present tube set is a few years old. In my experience, good old tubes are often waaaay better than mediocre new ones. Wholesale replacement of entire tube sets for no pressing reason is generally a real waste of time and money, much like changing oil every 3000 miles, even though current oils are good for two to three times that long. Tube and oil makers love it.....but it's really not necessary.

[@djfrank59]

I agree! I try to avoid Chinese tubes because they are a dice roll; out of 20 tubes, you "might" get one that's decent. If it's an old vintage amp, I try to convince the customer to go with NOS tubes (and only the one's that are truly defective) Chinese 12AX7's are another headache. they're full of pings, dings & whistles. microphonics are a real problem with them. there were times I had to float the tube sockets with rubber grommets to prevent any vibration getting into the tube...the shields simply weren't enough.

[@bepone1904]

hello mr doug, i just log in to your channel to express my strong support to your guides and big respect in very useful analitiyc videos..maybe too late, but i can add here something positive about this small russian 6P6S (6n6C) tube , rebranded chinese - it is sturdy and cheap 13.5w 6V6 type tube, what you can buy it for 2-3 usd.. most use it found in russian TV sets in output audio sections..some test showed that this small black bomb can withstand 500V anode and g2 without breakage.. characteristic is like you can see shifted 20% so bias need to be adjusted in comparation to 6V6..here in video we have too big voltage problem on g2 which is the "main flow valve" in the system.. so closing the flow (lowering g2 voltage by adding series resistor..from 1-5 kohms 5W with g2 ) will lower the anode current a lot -- so cathode resistor can stay untouched.. i usually take this method .. keep up the good work i just bought tolex to copy your method! (tolex tutorial- :)

[@UncleDoug]

Wow, thanks for the very kind words and detailed input on a tube I never heard of, the 6P6. It definitely sounds like an interesting and economical alternative to the venerable 6L6. Thanks for sharing this information, and best of luck with your projects !!

[@moodyga40]

rocking lot of juice red plating lol

[@W1RMD]

Beautiful amp and great video! I know it's been a long time, but I'm curious if you can remember how the Chinese tube performed with the 802 ohm bias resistor, or did you just stick with the GE tube?

[@UncleDoug]

I don't recall, Ryan. It's simply a matter of trial and error until the proper PD is achieved.

[@danielcrook9504]

We used those green stamps,at least my Mom did and you're right ! S&H green stamps. I must have been 7 or 8 and looked at them a time or two ! A bygone era and method to get customers to save these up.for trade and promos...!

[@UncleDoug]

One of my fondest childhood memories, licking, sticking, and going to the redemption store to get new stuff.

[@danielmargolis3210]

Various 6v6 tubes can sound very different in Vibrochamps. I have an original (not reissue) Tung-Sol in mine which sounds fantastic.

[@UncleDoug]

Thanks for the tip, Daniel

[@leew5624]

Just got this amp today at a yardsale for $10! So stoked! Afraid to turn it on though

[@UncleDoug]

Wow....great acquisition. Build a Current Limiter (see my video) to protect the circuit before you plug it in.

[@leew5624]

@@UncleDoug will do, havnt plugged it in yet just for that reason!

[@MrTartlet]

Nice to see another video from you. I wanted to ask you a little question: recently I experienced redplating with Tung-Sol reissue 6V6 (as it turns out they are limited to a very low 300V PV) even though they sounded well and otherwise were in spec for your average 6V6. So I was wondering: is it really that bad/dangerous to be running a tube that is redplating?

[@UncleDoug]

Greetings, AR. Yes, I believe that plates operating at "red plate" temperatures can actually melt and sag into contact with other components within the tube. Such contact could result in a short circuit and rapid destruction of the power transformer, rectifier tube, etc. Depending on how the 6V6's are biased, you need to significantly reduce the plate current, either by increasing the negative grid bias or increasing the cathode bias resistor value.

[@daleburrell6273]

...operating a vacuum tube at an excessively high temperature- is NEVER a good idea.

[@tubical71]

Nice litttle Amp and a good video, i would have done the same, as you did for the Amp :) I would have save the china tube for myself, if the owner is ok with the replacement JAN, and figure out what is going on.... I got here an EL34 witch have nearly twice the mA/V (=gain) characteristics than any other EL34. But everything else is of with this "special" EL34. It was from an 4xEL34 Amp and all other tubes where just fine... I missed out on hearing the sound of the Amp, as you usually play some chords after repair...

[@UncleDoug]

Greetings and good to hear from you, TC. It is indeed an unusual tube, that tested quite well on the Hickok tube tester and actually sounded quite good in the amp. I did test the amp after completing work and it sounds about the same as before the repair.....but without the excessive heat. Since there was no demonstrable change in tone, I chose to forego a video sound check.

[@SuperCarver2011]

Uncle Doug, you really know your Fender amp S/N. I remember those gold bond stamps from the 50s. I would get them from my mother, lick them and put them in a book to redeem them for prizes..fishing rod and reel. Looks like Rusty is just not into amps..it seems. Leo Fender started out building amps..he was good at them..the guitars came later. I would throw out those Chinese tubes..same with the Sovteks..yes they are supposed to be equivalent, but they aren't. Nothing like the old NOS RCA or other US manufactured tubes in your vintage amp. Very good discussion on addressing plate dissipation to keep those power tubes from cooking. I got a Peavey ValveKing and the first thing I tossed out were the electro-harmonix preamp tubes and the sovtek 6L6s. Got some better and still affordable tubes from a well known online tube seller.

[@UncleDoug]

SuperCarver2011 Thanks, SC. In the 1950's, my mother and I spent many a happy day pasting S&H Green Stamps into booklets.....for a new toaster, ironing board, etc. We used a damp sponge, thank heavens, or I would probably have developed a speech impediment.

[@bart99gt]

I caught a glimpse of the back panel that it was designed for 117 volt operation, so there shouldn’t have been a huge difference in the B+, maybe 7-8 volts at most. Since those old schematics said to allow for about a 20% variation in voltages, what you measured pre and post repair were still close enough. Makes one wonder if something else was at fault, like a leaky cap or wrong impedance speaker.

[@UncleDoug]

Fender tended to bias their small amps quite hot, Bart, probably to enhance early breakup......and tubes were much cheaper then.

[@Rod_Knee]

Hi Doug, Another excellent, informative video. I have a question, though. What was the plate dissipation of the Chinese tube with the 802 Ohm cathode biasing resistor?

[@UncleDoug]

That was a long time ago, Rodney, and if the answer is not in the video, I would have no way of remembering it.

[@Rod_Knee]

@@UncleDoug: Thanks regardless. Your videos are great.

[@tomk1tl]

Hi Doug,I just removed a 470/ohm resistor (measured 510/ohms) from my home built 5F2(A) as it was running around 18w plate dissipation also. The plate voltage is 385VDC, which I thought was very high for the 6V6. What I did was order an 820/ohm 3w resistor...what I should do is put a 5K pot to have "adjustable bias" for the tube. I now know why the cat loved to sit on top of the amp case as it definitely did get very "HOT" indeed. I will let you know my results when I do the mod...otherwise, the amp sounds great...just awaiting parts !

[@UncleDoug]

Greetings, Tom. Yes, your PD was about 50% too high.....not a good situation. A 5K pot would be overkill, but a 3 to 5Watt 1K precision adjustable resistor would probably do just fine (see my video on the Fender Champ built from spare parts). Keep us posted on your progress.

[@tomk1tl]

Hi Doug...just installed a 1K/3W resistor in the cathode circuit. Got PD down to 11.2W which should be OK as it is about 1W below max rating for the 6V6. Would have liked to get it around 9-10W. I could have still messed around with swapping out resistors or changing tubes but this should be OK. Ip = 0.029A, Ep = 378VDC.

[@ericguglielmetti7583]

Hey Uncle Doug! I absolutely love your channel. I'll get straight to the point though. I have a 1968 Bassman head that I bought modified. The preamp is AB165 but the phase inverter/power section is AA864. I personally biased the amp recently and am confident i did the math correctly. I have 49ma on the plates at the moment, which some might say is high, but i think is acceptable . Anyway, the power tubes are not red plating, but I realized the power transformer is running quite hot. It isn't nearly as hot as the power tubes but it gets quite toasty after an hour or so. I can hold my hand on it for a while but im worried it might be getting too hot. I know Fenders are notorious for high plate voltage and getting hot in general, but is there a precedent for transformer heat? Would increasing the bias resistor value help? Unfortunately I don't have an infrared thermometer so I cant give you an exact temp. Any info you have would definitely help. Thanks Uncle Doug!!!

[@UncleDoug]

Greetings, Eric. The plate current (in Amps) is only half of the biasing procedure. You must also know the plate-to-cathode voltage and then multiply to determine the plate dissipation, which must not exceed the maximum for the tubes you are using. You may need to reduce the PC to achieve the proper PD value. If your PD is proper, your filter caps are OK, and your filament circuit is not drawing too much current, then (unless your PT is inadequate for the Bassman circuit) there should be no excessive heating problem.

[@stevegardner6461]

hello Doug thank you so much for your videos. I have a I think a 64 vibro champ amp. I have watched a couple on your videos on this amp, and due to your info it has set screws at the 10 o'clock position. With a red jewel power indicator. Recently it developed a hum. It seemed to be in the speaker cable cause it went away when you jiggled it. It was a poor quality cable from a best buy. I got a real nicely shielded cable this helped, but the hum has returned. I tried to op check the unit, and when I wiggled the filter capacitor it helped even more. Now I have a hum the responds to volume control and is quiet till about 5 on the volume. So after watching your videos I'm pretty sure its the filter capacitor. Any suggestions. Also I should mention the speaker has been sawed off this unit. It has a RCA cable going to a 1/4 inch input jack pushing a Laney 2 x 12 cab. Thank you so much for your info very informative.

[@UncleDoug]

+Steve Gardner Steve, as the video explains, you need to determine the frequency of the hum. if it's 120Hz, then it's probably from the filter caps. If it's 60Hz, then there could be many possible causes and you will need to either check Internet sites for a diagnosis or take it to an amp tech.

[@PadraicPlaugher]

great tech work uncy doug! How did you adjust the bias?

[@UncleDoug]

Just like I showed in the video, PP. I used trial and error to find a cathode bias resistor that provided an acceptable plate current and plate dissipation value :)

[@zamourdeki]

By installing a VVR in an amp you can reduce the plate voltage of the output tube.

[@UncleDoug]

I have been reading up on Variable Voltage Regulators, Zam, and find them quite interesting. They allow you to reduce the plate voltage in your output tube(s) without affecting the filament voltage. Thus, they can act as an attenuator to reduce your output power but still retain the distortion associated with the higher plate voltage. I suggest that interested viewers should do some searches to find out more info on the Internet. Thanks for bringing up this subject.

[@SlungStrat]

Rusty winks at 3:18

[@UncleDoug]

It's for his girlfriend, Georgette :)

[@imannonymous7707]

say hi to rusty for me plz lol cheerz great job.....both of yas

[@UncleDoug]

Thanks, Rick. I will :)

[@moodyga40]

wow 89c for tube must have been long time ago here $30 for 1

[@rgigliotti7576]

UD. great vid, I'm working on a black face champ and my power spy is rnning high, around 450 making all the plate voltages 30 - 40v hi. y line oltages rns around 120v. . Shold I change the dropping resistors in the plate supply to compensate well as setting the final bias? tnx RJ

[@UncleDoug]

Greetings, RJ. High plate voltages are pretty typical in older Fender amps. You need to check the plate current and plate dissipation. It's possible that the PC is low, making the PV higher. Bias the output tube to a PD of 11 to 12W and the PV will probably be lower. Regardless, it's the PD that really counts, and if it's normal then you're OK.

[@rgigliotti7576]

Thanks Doug, I'm running about 16w PD at the moment so I need to increase the bias resistor. However, I'm also concerned that the plate voltages on the preamp and the the filament voltages are high as well, About 233v and 238v. on the preamp plates and filaments 7.1vac. Should I worry about these voltages as well? ;-) RJ

[@abeanx]

hi doug, love your videos man! Just wanted to say i followed your instructions to find the plate disapation on my 1970 silverface champ and i got a reading of 20.9w following your directions to the T. Yesterday while playing my amp it started making loud static and popping noises so i shut it down, and then took off the back and powered it back on and got the static popping again and noticed the power tube was arching white inside the 6v6 i thought the tube might be bad so i swapped in a new tub sol 6v6 and after about 2-3min of being on it did the same thing also the tubes where all bright red i belive they were "red platting". The only thing i have done to the amp is replaced the bias resistor and capacitor next to it because the resistor melted the capacitor i replaced the stock resistor with a 5w 470ohm resistor and the capacitor with a silver sprauge 25uF at 50VDC capacitor and the amp has been great up until last night. I also did the NFB loop mod but that is it. I asked around on a forum and they told me to check pin #5 on the power socket to see if it was getting voltage and it was it got all the way up to almost 150 on my meter before i shut the amp down so they were telling me that by replacing the bias resistor like you are saying in this video would be wrong since mine is a new resistor and is within spec that by increasing the resistor value with a bigger one would just be masking the problem? Do you feel the same? They said to test the coupling capacitor that is connected to the #5 pin because it could be bad and letting the wrong current threw and thats what is causing the arching and high plate disapation? Any thoughts? My email is [e-mail] if you could maybe email or just reply here if fine as well. Thank you so much in advance!

[@UncleDoug]

Greetings, Aaron. I'm sorry to hear that you are having problems with your SF Champ. First, 20.9W of plate dissipation is way, way too high and would probably cause red-plating. Maximum PD for a cathode-biased 6V6 is about 12W. I agree that before you install a higher value resistor to bring down the PD, you should check to see if there is not another problem causing the high current flow through the tube. I wonder if the Sprague 25uf capacitor you installed may not have an internal short circuit, or if it is installed backwards. Check to see if it is - to ground and + to pin 8, NOT the other way around. If it's in backwards or shorted, the result would be very high PD (just like you have). You could replace the one you installed with a new 25uf capacitor and be sure it's installed correctly. You could also simply replace the .022uf coupling capacitor between pin 6 of the 12AX7 and pin 5 of the 6V6. It's easier to replace the cap than to test it. If the high current problem ceases then you know the cap was at fault. Let me know how this works out. Good luck.

[@abeanx]

I originally installed the cap in backwards and the people on the forum caught that luck ally before I powered the amp up so I know for a fact it is installed the right way. I did notice a little oil coming out of the end closest to the pots I may try replacing it and seeing if that helps I have a spare capacitor the exact same kind I will try that really quick and see and get back to you! Thanks for the quick reply Doug you are awesome!!

[@UncleDoug]

Oil should never leak from an electrolytic capacitor. Something is either wrong with it or it is receiving higher voltage from the amp circuit than it can handle (which should not be happening). If you have a spare .022uf cap, replace the coupling cap to pin 5 of the 6V6.

[@abeanx]

I have a few caps laying around here are the specs... Sprague 25uf-50vdc Sprague 20uf-50vdc Will either of then work to replace that coupling capacitor? I think it's a 20uf? I may be wrong tho you are the expert :)

[@UncleDoug]

No, the coupling capacitor must be .022uf at 600V. You have to be very careful with both the capacitance (.022uf is completely different from 20uf) and the voltage (it has to be 600V for the coupling cap, nothing lower). The 25uf at 50V is a cathode bypass capacitor, like the one you installed from pin 8 (+)of the 6V6 to ground (-).

[@brianhensley7161]

Hello Uncle Doug.... I have a couple of follow up questions after this Vibro Champ video...I reset the Bias for mine to about 9W Plate Dissipation.(1.2k resistor)...surprisingly the amp still has a lot of breakup at the same volume settings.... 1. Will the "headroom" for this amp improve with a more efficient Output Transformer ? if not, 2. Where does most of the "distortion" occur? Thank you for your time, can't wait to get more into the new "Resistors" video....

[@UncleDoug]

+Brian Hensley I'm assuming that the PD before you increased the bias resistance was higher......probably around 12W, which is max for a cathode biased 6V6. I'm surprised that a reduction in PD was not accompanied by an increase in headroom, which is what is normally seen. Are you sure that your speaker and pre-amp tubes are in good shape? If so, then perhaps lowering the PD even more might provide the headroom you seek. I don't think the efficiency of the OPT is an issue. If it's the original OPT, then it should be just fine. If not, then the winding ratio of the replacement has to be correct to match the impedance of the output tube (around 5K) with the impedance of the speaker (it varies with different models and years.....probably around 4 ohms). Distortion can occur first in the pre-amp tubes if they are overdriven, i.e. by a very strong guitar signal or a booster pedal. This overdriven signal is then sent to the output tubes where it is either faithfully amplified (if the tubes can handle it, i.e. cool bias) or the signal overdrives the output tubes. Also, it's possible for the distortion to occur only in the output tubes, especially if biased rather hot. Thus, the "good" type of distortion always originates in the tubes.....pre-amp, output, or both. Speaker distortion is generally unpleasant and purely due to too much volume for the speaker to handle.

[@doctorspicer1042]

Just got myself a champ 40🙂

[@UncleDoug]

Congratulations, Doc :)

[@doctorspicer1042]

@@UncleDoug thank you 🙂

[@BrickwallJackson]

EXACTLY the problem I have with mine!! The question is: What doesn't Uncle Doug know about amps? The answer is nothing. There is nothing that Uncle Doug doesn't know about amps. . . :)

[@UncleDoug]

You are too kind, BJ. Actually, it's Rusty who does all the diagnosis....generally by sniffing components. I just do the repairs that he authorizes :) :)

[@elmadouf]

Hi Uncle Doug ! A friend of mine would like to modify his Wurlitzer 200 keyboard by installing an on-board tube amp. I suggested installing a Vibro champ circuitry with solid-state rectification (to save space), and maybe even a transistor base oscillator for the trem. I think this little amp would work wonders, since it's already very appreciated as an auxiliary output. Would you recommend this kind of installation ? My main concern would be the heat.

[@UncleDoug]

If your friend wants Tremolo effect for his piano, I guess that would be a good idea, Francois. I am not a big fan of changing to diode rectification in small amps, or substituting transistors for tubes......but if you are able to do this for him, then best of luck with the project. Either way, I don't think that heat would be a major problem.

[@silvertoneize]

Hello Uncle Doug, Love your videos. Can I send you an amp for repair or an overlook? I don't know if you do this for a living or just as a hobby. Thanks

[@UncleDoug]

+RemedyZ Greetings, RZ. Glad you enjoy the videos. I am retired now and don't do outside work, especially if it involves packing and shipping.....but thanks for asking. Hopefully you can find someone locally to check it out for you. Good luck.