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

[@Classix1969]

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

[@UncleDoug]

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

[@jdb2722]

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

[@UncleDoug]

Thanks, JB :)

[@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.

[@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.

[@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 !!

[@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 :)))

[@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 :)

[@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 :)

[@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 :)

[@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.

[@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.

[@DavidWren-u3k]

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.

[@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 :)

[@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.

[@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.

[@brentatkinson73401]

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

[@UncleDoug]

Thanks so much, Brent :)

[@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 ;)

[@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 ?

[@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.

[@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 :)

[@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 :)

[@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.

[@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 :))

[@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.

[@dtotheatothevtothee]

Excellent video, sir!

[@UncleDoug]

Thanks, Dave. Glad you liked it!

[@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.

[@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 ;)

[@1980bwc]

Rusty's wink was perfectly timed.

[@UncleDoug]

He was a skilled actor :)

[@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.

[@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.

[@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.

[@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.

[@rodneykroetsch2924]

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

[@UncleDoug]

You're welcome, Rodney :)

[@moodyga40]

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

[@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.

[@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.

[@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 :)

[@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 :)

[@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 :)) ^. .^

[@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.

[@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.

[@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 :))

[@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.

[@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 :) ^. .^

[@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.

[@drbryson2]

I have a question about the pots. I noticed (at 5:35) that the back side of the pots have two different styles. Two pots are smooth and the other three pots have a smaller center shaft on the backside. Why the difference? Did Fender use pots from two different suppliers? In my '65 BFDR eight of the pots are smooth and the first volume pot is the only one with the small center shaft.

[@UncleDoug]

+drbryson2 I have no idea why the pots are of different configuration, DR, but I'll bet the farm they are original to the amp. Perhaps the structural differences are due to their different resistance values. I would imagine that Fender would have used pots from Outer Mongolia if the price was right and they actually worked OK, and they may have had parts bins where pots of equal value but from different manufacturers were mixed together.

[@BrickwallJackson]

Best dadgum channel on KZbin!!

[@UncleDoug]

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

[@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 :)

[@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 :)))

[@iyup2964]

Thank You! Nice video.

[@UncleDoug]

You're welcome :)

[@josesaldivar655]

Greetings to Rusty too

[@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.

[@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 :)

[@markgrimm3564]

uncle doug what tube tester are you useing and what is your opion on good bad and the ugly on tube testers and once again thanks so much for your time in sharing this with us

[@UncleDoug]

I use a Hickok 600-A, Mark. They're a useful tool that you can generally get dirt cheap at garage sales.....or not-so-cheap on Ebay. The one drawback is that amp problems are very rarely due to the tubes.

[@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 :)

[@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.

[@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.

[@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.

[@leewar40]

Rusty for President!

[@UncleDoug]

Thanks, Warren :)

[@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.

[@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 (-).

[@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.

[@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 :)

[@holmes1978]

So Fascinating !!!

[@UncleDoug]

Glad you liked it, LH :)

[@latouselatrec]

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

[@UncleDoug]

Thanks, Marco.

[@gringopig]

Great info Doug!

[@UncleDoug]

Thanks, GP :)

[@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.

[@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 ?

[@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.

[@captainfineweather5610]

RUSTY RULES !

[@UncleDoug]

Yes, indeed :) Thanks, Capt.

[@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.

[@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

[@donrutter6765]

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

[@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 !!

[@DeathByViny]

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.

[@DeathByViny]

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

[@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.

[@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.

[@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.

[@HDDog2]

AS far as the circuit running "hot" in old Fender Amps... How much difference is there between household plug voltage back in '65, compared to today ? Back in the day, the standard used to be 110 volts, where today my voltmeter shows a good 120 to 125 volts. A 15 volt difference may seem small, but, what would the output voltage be on the power transformer with the 15 volt increase on the input ???

[@UncleDoug]

The hot bias of old Fender amps can't be completely explained by the outlet voltage increase. Wall voltage has increased about 9 to 10%, yet the bias in many of these old Fender amps is 25 to 50% too high. The fact is, they were biased really hot from the factory.......probably for good tone, and replacement tubes were cheap back 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.

[@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

[@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 :)))

[@russellnelson5768]

Hey Rusty, What is that black material the circuit components are mounted to, and how are they soldered together? It looks like wood, and the components are just soldered on top, but that doesn't make sense...

[@UncleDoug]

It's a thick, black paper material called "eyelet board". The brass eyelets are installed in the board in strategic locations so the electrical components can be soldered to them and to each other to complete the circuit. It was used in virtually all of Fender's pre-printed-circuit-board amps. Here is a site discussing the different types of circuit construction: www.aikenamps.com/index.php/is-point-to-point-better-than-pcb

[@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.

[@shadiah1]

Great video Uncle Doug. Have you ever worked on an Ampeg V4? I would love to have the tube biasing explained on it.

[@UncleDoug]

We have not, S1, but virtually all amps bias the same, depending on whether they are cathode or grid biased.

[@joemcgraw5529]

I have a ampeg v4 had it for years had many issues ,took it to a local amp tech and he fixed all the issues many caps were replaced ,the 2 wire ac cord was replaced ,all tubes basic all around overhaul but wasnt cheap about $650 but everything was done correctly and the main thing was biasing the natching tubes now this was 2005 ,so my cost a little more but the output tubes were about $120 ,so i was happy to pay him since I bought the amp and sunn 4x12 cabinet for $100 back in mid 80s it is very loud to say the least ,auditorium worthy not bedroom worthy lol it will shake the whole house at level 5

[@joemcgraw5529]

I will also add that iwas vetry lucky i didnt electrocute myself from the condition filter caps had been leaking for years ,and with a 2 wire ac cord it would have been very easy to be toasted ,the tech told me this and also told me i was lucky the transformer wasnt roasted then it would have cost close a $1000 to fix ,which is what this amp is worth now about

[@UncleDoug]

I'm glad you view the money spent on restoring a classic old vintage amp as a reasonable investment, Joe. You simply can't find that type of tone and quality in production amps nowadays......even at a higher price.

[@shadiah1]

I always laughed at younger guys who thought that a 100 watt tube amp couldn't produce nearly as much volume as their 1000 watt stereo. Then we would put them in a room with a VT22 turned up a bit....always a surprise.

[@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.

[@ijamsum]

That 6v6C tube is a freak ! It has the power of a 6L6 ?

[@UncleDoug]

No, a 6V6 is not as powerful as a 6L6, particularly a 6L6GC.

[@allanpennington]

Hi, I am working on a clone of a Vox amp and wanted to use thermal flow simulation to assess the 60's cab design and orientation of the amp chassis. In the Vox amp the tubes face down (like many amps) inside the cabinet. I am not sure how to apply a value for the tubes in the chassis which for the simulation is input as Watts. Forgive my obvious lack of electronics knowledge but is there a relation ship between the Watts and external Temperature reached by a tube. The tube data sheets dont show a working temperature range. The flow simulation should show if the heat convection to the components in the chassis is better or worse depending on its orientation, which is the aim of the study. Some people have added fans to their old amps as they have a concern about heat, and some swear that the hotter an amp runs the better it sounds. However there must be an ideal temp range or at least max that a tube should run before its life span is dramatically reduced. There is also transfer of heat through the chassis from the tubes to other components on the turret board and I have often wondered if the amp is better off in an 'upright' config whereby the heat from the tube rises up and out of the cab, without passing over the rest of the components as apposed to the 'upside down' config.

[@UncleDoug]

Common sense would dictate that having the tube globes facing upward would enhance their ability to shed heat. The only reason that chassis are hung upside down is to make the controls accessible from the top of the cabinet, rather than the bottom.....especially the bottom rear, as they often were in vintage amps. Tube heat is somewhat of an issue, but not a critical one as long as the tube plates are not overheated by excess current flow. If you are designing an amp with thermal efficiency in mind, I would place the chassis on the floor with the tubes aiming upward and plenty of opening(s) in the rear panel to allow for good circulation. If there are four output tubes and/or two rectifiers, I would add a small computer cooling fan.

[@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

[@gengster247]

Uncle Doug that could be a 1964, or very very early 1965. But it was built by Leo's guys with the FEIC wording on the faceplate. In 1964 the VC did not have a Fender logo on the grill. What is the serial number on the chassis and dates on the transformers and pots?

[@UncleDoug]

+gengster247 It was a customer's amp, G, so it's no longer available to me; however, the serial number should be evident in the video. It's probably what the 1965 dating was based on.

[@GarrickDavisWorld]

One of the biggest regrets of my life, nowadays anyway, is that I sold my pre CBS Vibro Champ on Craigslist back in 2001. My dad and I found it in a pawn shop for $99 in ‘71. I was 13. We made payments on it and it served me well even though I got bigger amps over time to be heard in a band situation. Divorce can make you lose your mind...for a while anyway.

[@UncleDoug]

I understand completely, Garrick. Many of us have lived long enough to amass a long list of serious mistakes. About all we can do is learn from them, and do our best not to repeat them.

[@GarrickDavisWorld]

Uncle Doug, thank you for your response. I just wasn’t so savvy about gear, at least as much as the guy who came and bought was I was selling. I believe I sold it for $200. My regrets are only that I, like so many, have discovered the beauty of these low watt amps. I do own a ‘66 Bassman head. Tone for days....thanks for sharing your expertise and passion.

[@UncleDoug]

You're welcome, Garrick. If you ever tire of the Bassman head, I have $200 to offer for it ;)

[@GarrickDavisWorld]

😂😂😂! Thanks for the “test”!!!!

[@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.

[@moodyga40]

love the American tubes

[@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 :)

[@briankisker6719]

On the topic of cathode resistors. mojo-tone uses 270 olm cathode instead of 250 from the original fender specs, what will the results be? lower plate dissipation?

[@UncleDoug]

Yes, Brian. Any increase in cathode bias resistor value reduces the plate current and thus the plate dissipation. In this case, the reduction due to only 20 ohms would be minimal. When you get the amp completed, you may find it necessary to alter the 270 ohm value (up or down) to achieve the proper PD value (12W or a little less for 6V6's).

[@raymondheath7668]

Always love the math!

[@UncleDoug]

It's God's language, Raymond :)

[@briankisker6719]

Uncle Doug and Rusty Your videos are great! In fact, they inspired me to build a mojo-tone 5E3 deluxe guitar amp! Its a challenging project and I'm in need of some direction. The layout diagram for the 5E3 deluxe does not give exact wiring connections for the ground wires. I'm writing for some advice about the wiring connections. I heard separating the preamp from power side using a bus ground works the best at reducing unwanted noise. I would greatly appreciate you help on the grounding wire connections. The layout shows (3) grounds off the turret board, (1) with power chord, (1) with the pilot light with 100olm resistors, (1) for the tone pot and (1) for each of the two volume pots. Where do they get connected? Thanks Brian the fellow Math Teacher !

[@UncleDoug]

I see about 8 chassis grounds in the Mojo-Tone schematic, Brian. What I generally do is place a grounding lug (small metal strip with a #8 or #10 hole at one end and a small hole at the other) under the nearest available bolt or nut, turret board support, transformer stud, etc. making sure it is screwed down tightly to the chassis, then solder the wires you want to ground to the free end. For the volume controls, solder the ground wire to the metal body of the pot. If you can, ground the power cord (green wire) and the negative ends of the filter caps to the same ground lug. If the kit has no ground lugs, you can make your own or (maybe) they're available at Radio Shack. Good luck !!!

[@briankisker6719]

thanks a ton !! give rusty a bone for me!

[@UncleDoug]

You're welcome, Brian. Rusty usually eats the meat and gives me the bone......

[@doctorspicer1042]

Just got myself a champ 40🙂

[@UncleDoug]

Congratulations, Doc :)

[@doctorspicer1042]

@@UncleDoug thank you 🙂

[@PeterWalkerHP16c]

I've now seen you drop the plate current on several amps that were scary high. Makes you wonder why Fender designed them so hot? Maybe the plate resistance or cathode emission for the OEM 6V6 was different or the tubes were so cheap you could hammer them like tyres at the staging lane.

[@UncleDoug]

I believe it was the latter, Peter. Super hot biasing produced "The Fender Sound" and tubes were cheap. I still have some NOS vintage 6V6's and they yield about the same PC, PV, and PD as the more modern tubes.