1965 Fender Bassman AA/AB165 Hybrid.......Schizophrenic but Sweet :)

This video features the rather extensive repair of a very unusual 1965 Fender Bassman with features specific to both AA-165 and AB-165 circuits, including several "unfinished" circuit characteristics. The initial issue was a completely fried 6.3VAC center-tap, but during its evaluation and repair, other unusual circuit peculiarities were discovered. Join us as we explore and repair this unique circuit.
Additional topics include alteration of the NFB circuit and use of the Polarity Switch to make it switchable, discussion of hum cancellation in 6.3VAC filament wiring, repair of my damaged Eurotubes bias probes, and modification of the Bass Channel tone stack to improve tone and favor guitar use for the customer.
If you would like to support our channel, please SUBSCRIBE and consider becoming a Patreon patron at: / uncledougsvintageamps or making a PayPal contribution to [e-mail]. We receive absolutely no ad revenue from our videos and rely upon our viewers for support. Thanks for your time and consideration.
Additional NOTES: 1.) The midrange tone control idea was deemed unnecessary. 2.) The audio demo was done with single-coil pickups (as Leo intended), NFB "off", and Tone Controls at neutral (5) position. 3.) The fact that the modified 6.3VAC circuit withstood hours of circuit and audio testing justifies, IMO, retention of the original power transformer.

[@TheGuitologist]

Always good to see a new Uncle Doug video.

[@UncleDoug]

Thanks, Brad. I hope you all have a wonderful Christmas :)

[@kevinking2468]

Uncle Doug is a real class act.

[@UncleDoug]

@@kevinking2468 Thanks, Kevin :)

[@VintageLabSilvioPinheiro]

He and you are one of those responsible for my appetite for the "lovely hot technologies" I try to keep in my modest and insignificant channel of deliciously outdated technology. Merry Christmas to you and a new year full of happiness. 73 DE PUSRZ - Brazil Thank you sir.

[@boboala1]

I know you busted your ass to type this vanilla comment - thank you!

[@tobiasgertz7800]

Uncle Doug will never have to wonder if he has made a positive contribution to society.

[@UncleDoug]

Thanks so much, Tobias :)

[@scuzz152]

More outstanding content as always, Uncle Doug! When clients of my little, post-retirement, amp repair business ask how I learned to do the work, I tell them 20% from the half dozen Tube Amp Repair books I bought, and 80% from your videos. All the tube jockeys posting content out there can only fight over who's the second best. Many thanks and glad to be a Patreon supporter!

[@UncleDoug]

Wow, thanks so much, Scott. High praise indeed :)

[@sharkskinboy]

I agree totally. I have seen a few other tube amp repair channels and while they were OK and largely seemed to know their stuff, they paled in comparison to Uncle Doug's outstanding explanations, attention to detail, and meticulous and well thought-out approach to troubleshooting. We've been spoiled terribly now, it's impossible to watch anyone else!

[@74cannelle]

@@sharkskinboy Yep. That’s where Uncle Doug makes the difference 😉

[@UncleDoug]

@@sharkskinboy Thanks so much, SB and 74C. We really appreciate your kind words.

[@TuanAnh-lg1rp]

He’s made of the same quality as many of these timeless fender amps, so I think he’ll be around for quite some time!

[@jlore6344]

Uncle Doug's videos are like meditation and therapy for me. These also inspire me to repair and mod my own amps and someday I plan to build one myself. Thank you Uncle Doug!!

[@UncleDoug]

That's great to hear, JL :)

[@BillMcGirr]

Not only do I enjoy watching his videos while I’m awake… But I let them run while I’m going to sleep hoping osmosis will take over. Besides being my amsr therapy. 🤣💪👍🎸

[@reggiewallace260]

Back in the very early 70's, I picked up a used 1965 Fender Bassman head to replace a Univox bass amp head that I bought several years earlier. It cost me $50 at the House of Guitars -- a wonderful guitar store in Western NY that I believe is still open. I paired it with a 2-12 bottom that a friend and I built with a couple of used Utah speakers. At the time I played bass in a local band. Eventually I switched to guitar, but kept the Bassman head around. Over the years, it was used by various keyboard and bass players. Once it served as an emergency replacement power head for a PA head. By the late 1980's, it was retired to a closet until my then 12 year old son decided to try playing bass in a band with some other kids. Eventually it started popping fuses and I had it serviced by a local tech who replaced a bag full of capacitors along with a few resistors. Interestingly, it still has it's original Sylvania 6L6GC tubes and RCA 7025/12AT7 tubes - except for one that was broken many years ago and was replaced by a GE branded tube I picked up at a local drug store -- remember when drug stores had tube testers and sold tubes? Love your videos Doug, thank you!

[@telecomex]

We had a tube testing "station" just as you entered the drug store here in vancouver. Most people used it to check the tubes in their tv. New tubes were in the cabinet below the tester. Man, those were the days!

[@rotaxtwin]

Drug store tube testers... Yeah they were a fixture everywhere. Last time I saw one was early 80s in a military surplus store, but it was still somewhat stocked with tubes.

[@reggiewallace260]

@@telecomex Yes! The tester right near the front door with tubes stocked in the cabinet below. lol

[@pneumatic00]

Great deal! I remember those heads selling for $125-$150 in virtually any quantity you could want.

[@UncleDoug]

Yes, I do, Reggie. Thanks for sharing :)

[@curtisphilumalee1447]

Paul Westerberg sound test sounded spot on. Thanks for the educational upload. It’s always refreshing.

[@UncleDoug]

Glad you enjoyed it, Curtis :)

[@highpath4776]

Thanks for the cat update, we lost one to a road car run over a couple of months back. Have gained a new one (rescue from an old lady that could not look after her) - just on a year old , quite small and has either lost a bit of tail or it is just short and she cannot jump very high so its a clamber to the cat house and does not know how to scratch against the fence posts to keep her claws short. Different personality , sleeps most of the day and wakes up at 8pm to play when the kids have gone to bed - and only meows to play at 6am in the morning with a short jump onto the bed, better than an alarm clock.

[@UncleDoug]

She sounds like a great addition to the family, HP. Give her our regards :)

[@davecooper5951]

Fascinating how those little caps and resistors can make all the difference. I once found a fault in a power station computer 'clock' board that turned out to be a tiny tantalum electrolytic that had been installed the wrong way around at the factory. (At the start of the shift we had just one working board, by the end, we had seven)...got me a nice promotion to boot !

[@UncleDoug]

Thanks for sharing with us, Dave.

[@jenniferwhitewolf3784]

A holiday gift for channel fans! Thanks Uncle Doug!

[@UncleDoug]

Thanks so much, Jennifer. Have a wonderful Christmas :)

[@WRytmieBluesa]

My dream is to build amp by myself one day. As a non-English person, I'm still learning a lot about how vintage amps are build here on this channel. Thank You Mr. Uncle Doug :)

[@UncleDoug]

I hope that our videos and others can provide you with the knowledge needed to achieve your dream, DM. Best of luck :)

[@WRytmieBluesa]

@@UncleDoug Thank You :)

[@UncleDoug]

@@WRytmieBluesa You're welcome, DM.

[@watcher4627]

I do so enjoy your vids. I am a child of the 50's and went through the Maelstrom of the 60's music experience (you HAD to be there!). I played Bass (Still Do!) and then went through electronics school (USAF PMEL Lowery, Denver 1975). My take, Please keep doing what you are doing as it explains a LOT of what the teachers were trying to explain to me then😁. May you experience Good Health and Peace of Mind for a Long Time!

[@UncleDoug]

Thanks so much, Watcher. Likewise on the good wishes.

[@timothyandrews2157]

I found this same issue when looking into my 1967 pro reverb amp. I had to find schematics for both AA and AB, PLUS the Bassman AA and AB. I thought I was going nuts. I also had the resister to nowhere at the Bias pot. Then I couldn't figure out which way to go with it. I wanted the amp to follow the Bassman as it's so revered but then found the Bassman had the same basic schematics as the Pro Reverb. I just shelved it out of frustration but this video has given me new hope. Thanks Uncle Doug for helping us less knowledgeable to figure things out! You are a blessing.

[@UncleDoug]

You're welcome, Tim. Glad the video was helpful.

[@ericjenks9596]

Been recovering from heart surgery this past week (only 36 years old), and it’s been lovely to watch your videos while I recover.

[@UncleDoug]

Glad to hear it, Eric (the videos.....not the surgery). Best wishes for a speedy and complete recovery.

[@stewartcohen7683]

I'm just so heartened to know that other folks find this as entertaining, informative and rivetting as I do!! I am particularly interested in the NFB details :) as I already have my slope resistor switchable between 50 and 100--this is a nice option.

[@UncleDoug]

Thanks, Stewart :)

[@maxdisbrow977]

Thank you for yet another insightful video. You have been a great inspiration to me and it's time to let you know that. Three years ago, I wanted a vintage Fender tube amp. I am cheap and they are expensive, so I decided to buy and build a Tweed Twin kit. I built that kit and housed it in my own scratch-built cabinet. It was a great sucess. After the build I thought "I think i can do this" and I was bitten by the vacuum tube bug. Since then, I have built several amps from scratch, based on Fender circuits but always with modifications and I have started collecting and restoring vacuum tube test equipment and radios as well. I have a room full of "stuff" now. My wife just rolls her eyes. I have even begun making some solid-state circuits and amps and started making my own PC boards. Now, my former guitar instructor from years ago has begun sending people to me for amp repairs. It's crazy. All of this means nothing. The point of my story is that you inspired me to build that first amp and that kick-started this wonderful new hobby that I am very thankful for. Making music has been one of my favorite hobbies for a long time, but now It's a hard choice to say if the electronics or the instrument playing is my favorite part of it all! I can't thank you enough for your videos. When i get stuck on something I can always find the solution in one of your videos. Your knowledge is unsurpassed, your delivery terrific and your pets are cool. Our cats just love to "help" me when I am building. So, thank you very much Uncle Doug. Thank you for sharing your knowledge with the rest of us. I wanted you to hear another story of how you have changed someone's life. We can all make an impact. Many choose not to. Merry Christmas to you and your family Uncle Doug, and may the coming new year be good to you. Take care.

[@UncleDoug]

What a wonderful note, Max, especially at this time of year.....it's definitely one of the best gifts I will receive. It's great to hear that the videos were both inspirational and instructional, and that you put the knowledge within them to good use. Best wishes for a splendid Christmas and New Year.

[@jeremiahlyleseditor437]

Brilliant work especially with that floating ground.

[@UncleDoug]

Thanks, Jeremiah :)

[@henrykpycha1637]

Thank you I don't write too many comments on KZbin. I am 71 years old and I have met many teachers in my life. You are the best the most talented teacher - thank you so much you helped me understand so many things related to electronics. Which made my life more interesting. Thank you again. Henryk

[@UncleDoug]

Wow....thanks so much, Henryk. We really appreciate it :)

[@MrMeik1970]

The bridge to nowhere 😁 Very nice Repair and greetings to the lovely Cats 👍🏻

[@UncleDoug]

Thanks, Meik :)

[@sharplespaul]

I did a negative feed back mod on my 66 bandmaster years ago and forgot what I did.The drinking years..opened it today…then found this video lol….I put the feedback loop on a foot switch.I’m thinking the same as the ground switch.I’m thinking of slapping in a 500k tone pot instead and removing ground switch and death cap.Thanks for another great video Sir.

[@UncleDoug]

You're welcome, Mike. Good luck with your project.

[@drrobert2120]

That's what I love about Uncle Doug..a relentless, tenacious, troubleshooter...Always a great video and learning experience!! Thanks Uncle...Have a great Christmas and Happy New Year!!!

[@UncleDoug]

Thanks so much, Doc. Likewise to you and yours.

[@kgsalvage6306]

I worked on a 69 Twin Reverb that was a combination of the AB763 and AA769. Was confusing at first. Transformer dates all were correct. Power transformer was from the AA769, the eyelet board from the AB763. Made it work and sounded great with a few mods similar to ones you do. I've tried the pot for variable feadback in a few lately. Works well also. Erotubes are going to give you great service. They want the positive exposure your channel gives them. They may do it for all customers, but probably not as quickly. Another good video! Thanks Uncle Doug!

[@UncleDoug]

Thanks for your knowledgeable input, KG.

[@alexbozas887]

Uncle Doug, you trully deserve an honourary Doctorate in logical thinking, analysis, problem solving and restoration. If only those brand new probes could be directed at the current world leaders with a good dose of common sense we would all be smiling.

[@UncleDoug]

Thanks so much, Alex. I agree that some serious "shock treatment" is called for with our current "leadership". Let's hope we all survive their incompetence.

[@CraigHollabaugh]

Looks like Uncle Santa delivered an early Christmas present for us to enjoy. Merry Christmas to Doug, your support staff, the tubaholics and patrons.

[@UncleDoug]

Thanks so much, Craig. Likewise to you and all the Craigettes.

[@acooper8910]

The wires from the 6L6 plates to the dead end on the tag strip - the AB165 had a pair of 220k resistors going from the tag strip to the pair of 100k plate load resistors. The other tag from the bias had, as you say, a pair of 10k resistors that fed onto the .022 coupling cap - it was a hum balance rather than a bias pot. Interesting about changing out the .1 bass cap - gonna give that a go on mine. Thanks for the tip (& doing the groundwork😀)!

[@kbkman7742]

Yep, if you are going to remove the 220ks I would have removed the leads from the plates too

[@acooper8910]

@@kbkman7742 Yeah, it doesn't really do to have all that HT sitting out in the open doing nothing.

[@UncleDoug]

Thanks for the detailed analysis, AC.

[@keithcarter9396]

Wow, Uc;le Doug, your persistence for perfection is remarkable and legendary. A job well done, I guess the amp now outperforms its brand-new state

[@UncleDoug]

Thanks, Keith. It did seem to work quite well.

[@bluesman97]

It's nice to watch this video's... I feel a whole lot smarter. Thanks again Uncle Doug.

[@UncleDoug]

That's our goal, BM ;)

[@tomk1tl39]

As always, you videos are the greatest and educational....every time I watch them, I learn something new each time. Glad that all the felines are doing well, Ollie, KC and Jack. I had five feral cats I was feeding up until about four weeks ago and two somehow left....about a week apart. The are all B/W and I now call them the 3 Amigos. One is what I call my 'shadow' as he had no problems 'adopting me'. I want to get all three together to bring to the vet to have them looked over. The other two are still a little cautious and don't get as close as my 'shadow'. Funny as I walk out to the mailbox, and walk back, all three are waiting for me half-way down the driveway. My buddy, I can pick up and he doesn't mind it at all...never had a feral cat do this. Winter coming too quickly and have to make a shelter...they used to stay under my shed but somehow are staying under the front porch...there must be something else living under the shed I suppose. Keep up the great work UD.......LIFE IS GOOD ! ! ! ! !

[@UncleDoug]

It's good to hear that your furry buddies are doing well, Tom. I find that the females adapt to humanity a whole lot easier than the males. We've been feeding a big male cat in the back yard for years, and he still hates us.

[@highpath4776]

@@UncleDoug I doubt he hates, just considers himself superior

[@UncleDoug]

@@highpath4776 He may be right, HP ;)

[@jeffbrooks7246]

Everybody has pretty much covered the bases. You remain the best in the game my good man. Thank you, thank you, thank you!

[@UncleDoug]

You're quite welcome, Jeff. Have a wonderful Christmas :)

[@wayshot]

Another outstanding video from every amp tinkerer's favorite uncle :-) Tried simulating the cap changes in an online tone stack calculator. The .1 uF cap makes the bass control only boost the deepest frequencies, below 80 Hz or so. Lower cap values make a wider boost and lessen the mid scoop. Minni meows "hi" to her friends across the pond. She's bored these days as it's cold and lots of snow outside, so she can't patrol the neighborhood or hunt mice. She laid curled up beside me on the couch as I watched the video, so Minni and KC looked exactly like mirror images of each other :-)

[@UncleDoug]

Thanks so much, Asle. When I perform tone modifications, I rely more on my personal hearing (such as it is) than calculations. I do appreciate your further analysis of the value chosen. Holiday regards from Jack and me to you and Minni :)

[@edwardhannigan6324]

I was suffering serious withdrawal symptoms Doug..! No videos from you for a month or so.. Thank God, for this fab Fender Bassman arriving to save the day. Great video, super informative with so many interesting instruction and tech tips. Thanks for posting Doug, and for reducing my anxiety...Stay safe, and have a great Xmas.. Ed..uk..😁

[@UncleDoug]

Glad you enjoyed it, Ed. Thanks so much. Likewise on the nice holiday wishes :)

[@slartbarg]

Aww yeah, Uncle Doug and it's a '65 Bassman? It's like an early Christmas present.

[@UncleDoug]

Merry Christmas, SB :)

[@catfishfry336]

Nothing more entertaining than seeing Uncle Doug fix whatever little red wagon is tossed his way. It’s obvious that many of those amps had parents or techs that had no idea what they were doing….Lol!…….>===>

[@UncleDoug]

Glad you enjoy our workshop follies, CF :)

[@rohankhemraj]

Thanks Uncle Doug. I was excited to see a new video in my notifications. My favorite parts of this video were your explanation of the virtual center tap, the way you were able to salvage the power transformer, and the noise reduction steps. This was a very practical video that I will apply to my builds.

[@UncleDoug]

That's good news, Rohan. I'm glad the video was helpful :)

[@framusburns-hagstromiii808]

Great job! Best explanation of how a virtual center tap works I have ever seen! Also great demonsteation of how nothing but a piece of wire can inject wierd noise or oscillation in a circuit, I have seen that exact same thing..it can be baffling, natural inclination is to reject that as a possible faulty component. Good troubleshooting methodology will save you! Thanks Uncle Doug...Cheers!

[@UncleDoug]

Glad it was helpful, FB. Thanks so much :)

[@Shim267]

My first amp was a 71' version of this. You couldn't be more correct about the fast and loose approach Fender was taking with the Bassman heads.

[@UncleDoug]

Thanks, Shim.

[@jackallen6261]

Thanks UD for taking us along for the ride on another wonderful video adventure as you repair yet one more piece of musical history!. I think I speak for all the viewers when I say we appreciate the sharing of your knowledge in these videos more than you know! Happy Holidays to you and yours!

[@UncleDoug]

You're quite welcome, Jack. Thanks for your nice comments and for joining us on this ampoholic adventure :)

[@rocklamarre9717]

Nice to see you back!

[@UncleDoug]

Thanks, Rock :)

[@AlbertvanDuin]

Thanks for yet another very informative video! Inspired by your videos I finally built a 5F1amplifier last year, my first experience ever with tubes. It was something I wanted to do for many years and watching your videos finally gave me enough confidence to start building.

[@UncleDoug]

That's great to hear, Albert. Best of luck with all your future projects.

[@kenhancock8931]

THX UNCLE DOUG :-) HOPE YOUR DOING WELL!!

[@UncleDoug]

We are, Ken. You too, I hope :)

[@jamesadams1064]

Lupe must’ve been on vacation. Great video Uncle Doug.

[@UncleDoug]

Yep, she's sunbathing on the French Riviera, James. Thanks !!

[@seansweeney3532]

my first Bassman was from a drum shop in Granite city IL... I asked him if he had any old tube amps and he said just that one! but it doesn't work! And it was a Bassman head, 1966, holding the door to his office open. I was prepared to get down and dirty and fix my first real amp, but when I got the tubes and quickly made a dim bulb tester... it came right on and I played it for ten years... that one was $35... and the panel with the fake grill was covered in gold Lamé, but I was happy it was just kind of laid on it and screwed down over the original cloth that was perfect... apparently all the bandstands and amps were required to look like that. lol

[@UncleDoug]

What a great find, Sean. Thanks for sharing :)

[@Finom1]

God Bless and protect you and your family, Uncle Doug!!! I have missed you because youtube stopped sending me notifications. Bless you for sharing your wisdom with us in every one of your educational videos. You have been planting seeds of wisdom in so many souls over the years. You Bless us with your true Altruism, education generations worldwide!!!

[@UncleDoug]

Thanks for your very nice comments, F1. We hope you have a wonderful New Year.

[@rgbplumbinghilton]

Great to get a new vid during the Christmas Holiday. Thanks Uncle Doug and seasons greetings from the UK. Rich

[@UncleDoug]

Glad you enjoyed it, Richard. Likewise to you all.

[@Scodiddly]

Another great video - reminds me I really should spend some time checking the health of my beloved old Princeton Reverb.

[@UncleDoug]

Glad you liked it, S. Get to work on the PR ;)

[@drop_dtuned6167]

Hi Uncle Doug and thank for sharing your experience. Very much enjoyed watching you work through the trouble shooting, moving from diagram to circuit. Many blessings to you as well.

[@UncleDoug]

Glad you enjoyed it, DD. Likewise to you all.

[@ritualdevices]

As always... Great video! Thank you Uncle Doug.

[@UncleDoug]

Glad you liked it, RD.

[@danielpirone8028]

Uncle Doug is definitely part of my big happy family!

[@UncleDoug]

Thanks, Daniel......that means a lot :)

[@ronnie5129]

Uncle Doug, you are the best,

[@UncleDoug]

Thanks so much, Cuz :)

[@chokkan7]

Thanks for another illuminating installment, UD. Glad to see that the family are all doing well. I had not perused the diagrams for these (AA and AB165s) before watching this video; Fender was definitely trying out different things. I noticed that the AB Bass channel's 2nd stage has a 470K local feedback resistor from anode to grid (I'd seen a 10M resistor performing a similar function in the older 5E6A model), but this smaller resistor would have limited the gain of that stage significantly, wouldn't you agree? The AA (which lacked that local FB) had a 500pF coupling cap from that stage to the driver, while the AB used a 0.1uF coupling cap in the same position; looks as though Fender dropped the gain in the AB in order to improve clean bass response (the larger cap on the AA would have probably been a bit 'woofy', IMHO)...I'm curious as to your thoughts on the subject, if and when you have time...correct me if I'm wrong. Please keep up the great work...

[@UncleDoug]

Your analysis makes sense, C7. I might discuss this in a future video. The concept of local feedback of the out-of-phase signal from plate to grid, moderated by a resistor, is probably not well understood by many viewers. Thanks !!!

[@charleslambiase5670]

Uncle Doug you're back 💜🙏🏼

[@UncleDoug]

Yep :)

[@Bleats_Sinodai]

16:30 here in Brazil it's common to find people who recondition transformers. In my town there's this great guy, Diamantino, and his work is absolutely excellent. Made me an isolation transformer (with a 110/220 primary) for a tube record player, and also a P.T. for a project I haven't built yet. The core in those transformers usually doesn't get damaged when they go puff, so they're salvageable for rewiring.

[@UncleDoug]

Thanks for sharing, BC.

[@l6srob990]

Another great video as always i have never heard or played a bassman the work you did sure made it sound great learn from all youre videos thankyou

[@UncleDoug]

Thanks, Rob.

[@fredgarvin4482]

Thank you Uncle Doug for the excellent explanation of the 100ohm virtual center tap. I finally understand that. this is one of the reasons why I joined pateron to be able to support you in a small way. I think I had asked about it in the past and you had answered, but I didn't get until this time.

[@UncleDoug]

You're welcome, Fred. Thanks for your patronage of our channel.

[@fredgarvin4482]

@@UncleDoug so my comment made me go check my account. last time patreon made a withdrawal was 5 months ago... I guess I lied to you. I for the life of me can't find my old patreon account... I will make an honest person out of myself in a few days or so. lol. probably happened when I got a new card.

[@UncleDoug]

@@fredgarvin4482 Thanks for caring, Fred. We hope you can get it straightened out :)

[@Paul-hk7ue]

thanks again for your knowledge.........best wishes in this holiday season.......stay safe

[@UncleDoug]

Thanks, Paul. Will do ......you, too :)

[@raycochrane3971]

When I started watching an HUGE thunderstorm began so I downloaded your video so I could watch it uninterrupted by power failures or the fear of frying. Excellent diagnostics and a GREAT result. The NFB made a BIG difference on this one...sounds great. Thank you.

[@UncleDoug]

Glad you enjoyed it, Ray :)

[@Pyrofries]

All the best Uncle Doug

[@UncleDoug]

Likewise, Pyro :)

[@JagStar]

Someone has probably already said this but, that extra terminal strip is another indication that this is a hybrid AA165/AB165. The AB165 uses that terminal strip to connect the 220K local feedback on the output tubes. Another two "roads to nowhere" in this case. I had almost exactly this same hybrid about 20 years ago. It was the second Bassman I ever owned and it confounded me to no end because it didn't match any of the published schematics.

[@UncleDoug]

Thanks for your insightful input, JS.

[@oscardelatorre]

playing thru my 65 bassman right now while enjoying your show!

[@UncleDoug]

Sounds like a great way to play along with Ollie and Jack :)

[@OzziePete1]

Always a good day to see a new video from Uncle Doug. Trust you are well, sir.

[@UncleDoug]

Thanks, Ozzy. Never better :)

[@andyk295]

Hi Uncle Doug and Happy Holidays to you and the critters ! Excellent video as always. Couple of notes: I saw a mod (not for a Bassman) that employed a .01uf Capacitor in series if one decides to keep the N. Feedback loop, keeping the low and mid frequencies down. Or else, disconnect loop for a more aggressive tone at lower volumes, insulating the wire. Another mod is to increase the resistor value in the loop. The other suggestion is to install the switch as in the video and install the .01uf cap across it. The cap reduces 'harshness'. My soldering has improved having built a PC board-based delay pedal from a kit. No globs permitted !! Thank you !

[@UncleDoug]

You can indeed tune NFB loops, Andy, by controlling what frequencies are returned to the amplification chain and thus which frequencies are (more or less) neutralized.

[@danielsaturnino5715]

I've been watching psionic audio channel also for some time now and I found out that moisture in those boards can leak dc from the B plus connection on the eyelets to other close components. You can actually measure some voltage on the board itself. Even on the cloth wire insulations and if they are touching anything it leaks dc. Fascinating :) Just thought I share the info as it can prove to be usefull sometime later. Thanks for the video!

[@UncleDoug]

Thanks so much, Daniel :)

[@bobr8565]

I too saw the video on psionic where the voltage leaked across the board that is good to know and I suspect easy to miss. Doug keep ‘em coming a lot of enjoyment!

[@UncleDoug]

@@bobr8565 Will do, Bob :)

[@thome1547]

Dear Uncle Doug, great, informative video with lots of small, but great impact, modifications. Have a great Christmas season.

[@UncleDoug]

Glad you enjoyed it, TM. Likewise to you and yours :)

[@bullthrush]

An in depth repair / tune up. Thank you for taking time to share the tips and techniques. The cats seem satisfied with the level of service and have moved in

[@UncleDoug]

Thanks so much, Andrew. I think it's the free meals that won the cats over ;)

[@bobmckenna5511]

So great to hear your great customer service story for the euro tube product. That is very encouraging in these times when so many companies distance themselves from supporting their products. Another wonderful video and tutorial by the way, my highest compliments.

[@UncleDoug]

Thanks so much, Bob. I agree, Eurotubes is a class outfit. I highly recommend their products and service.

[@ralley145]

Hope this message finds you well and surviving the current pandemic. Love watching your videos with the mounts of info and humor. I've been amazed at all the amps I never knew existed. Although some videos are lengthy, they are very detailed and eye-opening. Almost like being in school. I have been guitar crazy and collecting some, but now tube amp crazy and looking for my 1st purchase. Say hi to Rusty and Jack. Hope they are doing well.

[@UncleDoug]

We're doing quite well, indeed, Bob....and hope you are too. Glad you enjoy our videos :)

[@ralley145]

Many amps are older than me. 1956.

[@glenncollins4778]

It’s my lucky day. Uncle Doug and friends are here to visit.

[@UncleDoug]

Break out the catnip and beer, Glenn :)

[@Numb3r1]

Finally another hit for the ampaholics out there, including myself. Thanks alot Uncle Doug!

[@UncleDoug]

You're welcome, N3 :)

[@BB-wj5wk]

Thank you Uncle Doug for another great video. Your expertise and careful troubleshooting never ceases to amaze me. You sir are also extremely rare and I hope you know that! Wishing you and yours continued health and happiness, and happy holidays.

[@UncleDoug]

Thanks so much, BB. Likewise on the holiday good wishes.

[@oldguy5381]

That a fine amp, good to see a new video from Uncle Doug. Please have a Merry Christmas

[@UncleDoug]

Thanks so much, OG. Likewise to you and yours :)

[@MrTimcoronel]

thanks Uncle Doug, great troubleshooting and nice to see the cats are all well. Merry Christmas from Australia!

[@UncleDoug]

You're welcome, Tim. I guess it's summer when you all celebrate Christmas.....it's hard for us to envision that, just as it must be hard for you all to envision our wintery, snowy Christmases. Best wishes for the holiday season :)

[@JonnySoundSounds]

good call on the virtual center tap

[@UncleDoug]

Thanks :)

[@AldoSpadaroOfficial]

Thanks, now I finally dare to start correcting mine as well!

[@UncleDoug]

Good luck with your project, Aldo.

[@hestheMaster]

Whomever was in the chassis before you and replaced the electrolytic caps was although proficient in the repair work was quite messy when using the solder. See sharp edges of solder on some eyelet connections and minimal solder in many places. Love your problem solving techniques demonstrated here Uncle. Myriad of problems well investigated and solved. Have a Merry Christmas to you, your family and your furry friends!

[@UncleDoug]

Thanks so much for your analysis, HM. Likewise to you and yours :)

[@michaeldowning796]

Masterclass! Another Awesome Lesson, Thank You!

[@UncleDoug]

Glad you enjoyed it, Michael.

[@Jesse-B]

Patience and logic wins again Uncle Doug. I am not a tech, but I watch your videos because of the clarity of your presentation, which apart from the knowledge gained, has a very calming effect. I almost feel ready to tackle one of those little 5W Fender clone kits.

[@UncleDoug]

Thanks so much, JB. When you're finally ready, good luck with the project.

[@GuitarSmith.]

Got the new Uncle Doug video notice a little later than usual this morning so I wasn't able to watch it until after dinner. Uncle Doug and a beer is just as good as Uncle Doug and coffee. It's 13 degrees out there tonight and the cats will go out, but not without giving me a dirty look. Not my fault guys. Thanks Doug.

[@UncleDoug]

Hope you enjoy it when you're able, Martin. I've seen that look from my own furry pals.

[@GuitarSmith.]

@@UncleDoug I did, while having chicken fried steak and a beer.

[@jonnybeck6723]

GREAT bit of teaching! Thanx so much!! I was wondering about 'hum balance' pots and lo and behold, you covered it... Magic. As I write, Elvis is keeping my lap toasty and says "Hi" to your gang... Very best of holiday stuff to you and fam, Uncle Doug

[@UncleDoug]

Thanks for joining us, Jonny. Regards to your furry kids :)

[@JDPri77]

Wow. What a difficult diagnosis. How Fender did this transition amp at the time affected the issues that arose years later. Amazing work.

[@UncleDoug]

Thanks, JD :)

[@isidroramirez5339]

Morning uncle Doug I’m going to take the same upgrades to my amp i see the change is noticeable Thanks for the advices

[@UncleDoug]

I hope the outcome is favorable, Isidro :)

[@andrewwilliams5042]

Been watching for years, appreciate the shared knowledge and humor. Was especially interested in the virtual center tap with hum balance pot part since it pertains to an old Ampeg V2 I acquired 30 years ago and am now working on. Just a side note, I just realized today is December 7th.

[@UncleDoug]

Glad you enjoyed it, Andrew. Pearl Harbor Day.....lest we ever forget.

[@rjprivate]

Thank you uncle Doug for the good wishes and the great video. There is always so much to learn from you. All the best to you sir!

[@UncleDoug]

Glad you enjoyed it, RJ. Likewise :)

[@Projacked1]

As usual I understand about half of this, but wow....what an episode. We missed you Uncle D.

[@UncleDoug]

That still sounds like a step in the right direction, PJ. Thanks !!

[@alfredahye4552]

Alfred ahye from Trinidad and Tobago, Uncle Doug in the video there were two wires connected from the plates of the output tubes which ended on a two pin terminal and stopped, in an earlier model, two 220k half watt resistors were connected from those terminals to the plates of the phase inverters

[@UncleDoug]

Yes, they were Alfred, which is all the more mysterious.....almost like they began assembly using one schematic and then switched to another in the middle of the job.

[@Slugg-O]

That amp was in need of serious need of surgery and you extended its life by 50 years. The center tap fix was slick. When I saw the carnage I immediately started wondering which brand of OT you were going to replace it with. Fortunately no heart transplant was needed.

[@UncleDoug]

Thanks so much, Randy. It seems like I've had a run of complex, challenging repairs and failed transformers. Hopefully, the next one will be easier......yeah, sure :)

[@EJP286CRSKW]

Hammond make a drop in replacement.

[@UncleDoug]

@@EJP286CRSKW Fortunately, it wasn't needed :)

[@akrmfk]

I ran out of superlatives to compliment your effort uncle doug. Thus I'll just say thank you.

[@UncleDoug]

You are quite welcome, Akram :)

[@elwoodblue977]

Thanks for the tip on the carbon comp resistors and the random pops coming out of the amp. I have a Traynor YGM 4 with this issue.will be replacing the resistors with metal film

[@UncleDoug]

Either metal film or metal oxide are a good choice, Elwood.

[@russellsmith4615]

Thank you! I learn something with every video you issue, Uncle Doug! I've got a '66 transitional AA165/AB165 Bassman very similar to your example and after doing the standard refurbish (electrolytics, etc.), I modded the power section (starting with the input of the Phase Splitter) to the AA864 circuitry but kept the AB165 front end. However, like your example in the video, the Bass Channel sounds a bit weak and the Bass Tone Control has very little effect. I plan to open the chassis back up and see if I can make the same improvements via the changes you made with those two capacitors you highlighted on the first stage plate and the tone stack. I'll report back my findings. Thanks again to you and your feline technical staff for sharing your knowledge for those of us out here in the Interwebs. ;)

[@UncleDoug]

You're quite welcome, Russell. I'm glad the video was helpful. Best of luck with the Bass Tone modification.

[@russellsmith4615]

@@UncleDoug, it worked great! I changed out that 0.1µfd cap in the Bass Channel Tone stack and put in a 0.05µfd (Jupiter) cap and now the Bass Channel sounds so much fuller and the Bass Tone Control now has a nice range similar to the Normal Channel. I had forgotten that I had already removed that .01 Plate bypass cap in the first stage of the Bass Channel 7025 - with this simple modification, the Bass Channel sounds the way it should. I also did the NFB mod using the old Ground polarity switch that I had already disconnected (along with the death cap) from the circuit when I put in a new grounded power cable (like you, the hot power lead went to the accessory then to power switch first, then fuse, then primary). I love the grittier tone you can get at a lower volume setting with the NFB bypassed. Oh, I also solved one other intermittent nagging issue: the amp would occasionally pop loudly when it was sitting on top of the 2 x 12 cab and if playing at a pretty loud volume - certain notes would vibrate (resonate) the cabinet/amp head and cause this popping. I first tapped the doghouse with my trusty chopstick and noticed pretty loud microphonics and then continued tapping on the preamp tubes and voila! V2 turned out to be the culprit! I changed it out for a new Tung Sol 12Ax7 and all is now good to go! Many thanks, again, sir!

[@UncleDoug]

@@russellsmith4615 Thanks for sharing these successful repairs with us, Russell.

[@billsoule5824]

Great as always to see another amp up on the table and your expert diagnosing techniques! I am relieved the OT held up to the filament supply/bulb socket short after seeing the CT wiring. Hopefully the exposed wiring was the worst the wear from being in an oxygenated environment vs internal to the xfmr and that the owner caught it in time to save it. I'm working on my '63 Bandmaster right now and had seen the bulb go out momentarily when I measured the filament voltage a couple of weeks ago. Thankfully the socket connections are secure and orientated safely. Just needed cleaning. I want to thank you for the excellent video you did on the 6G7-A version Bandmaster about a year ago. It turns out that S/N is 26 amplifiers after mine, and as they say, things always come in threes. There is another amp currently on Reverb that is 12 amps from mine and well chronicled in internal pictures, literally sharing date codes on 2 of the three Shumachers and identical manufacturing stamps on the chassis.. needless to say your video and that Reverb seller's documentation gave me superb snapshots of that 2-3wk time period, 58 years ago!

[@UncleDoug]

Thanks so much for sharing this with us, Bill.

[@billsoule5824]

@@UncleDoug Thanks for your reply, Uncle Doug. I just thought of a question that I haven't been able to resolve. On a schematic such as Fender 6G7-A it shows a date letter revision convention of K-FJ. I remember in my mechanical drawing days revision drawings had certain letters you skipped in the alphabet. No problem there. You then dated them except we used numbers. This is obviously the date of the revision but I can't correlate the K and J to year-month-week-day convention, in other words what the x-xx convention is? Any help would be greatly appreciated and have a great holiday!

[@UncleDoug]

@@billsoule5824 I believe the code is M-YY. For the Fender Harvard the revision code is F-EF which is 6-56 or June 1956. This will work for the 6G7-A, except for the "J" (10)? So I believe that the J indicates zero (0).

[@billsoule5824]

@@UncleDoug That makes sense, so K-FJ is 11-60 and the later AA763 rev of the bandmaster J-FC would be 10-63, J is either 0 or 10 and that is the one unique letter like that. (A-L) - (A-J) (A-J). Thank you!

[@UncleDoug]

@@billsoule5824 It's the only answer that makes sense to me, Bill.

[@mattdoliver1984]

Brilliant it’s good to come and watch someone with such a wealth of knowledge like yourself Uncle Doug, easily one of me new favourite channels to watch 👍🏼

[@UncleDoug]

Welcome aboard, Matt. Thanks so much :)

[@boboala1]

Outstanding job/pedagogy here, UD! (In my next life I'm gonna do my math homework & be good at soldering/unsoldering!)

[@UncleDoug]

Thanks, Bob.

[@klauspopp8322]

Thank you Uncle Doug for great performance - as usual very exciting ! And so good, that Jack, Oli and Kacy had a contribution for all us viewers ! God bless yo.

[@UncleDoug]

Glad you enjoyed it, Klaus :)

[@BobBob-dv2qh]

UNCLE DOUG I love your trouble shooting methods. Possibly takes bit more time but is very definitive, precise and absolute. Not alot of "repair techs" in todays world are as thorough or really have the skill set needed to trouble shoot, deduce, repair and tweak amps like you do. I love watching your videos and this one in particular I found very informative. One thing that I think is cool about this video is the fact that with the customers permission of course you are able to use your experience knowledge and skills to tweak the amp to dare I say make it optimal in both sound and performance. Oh let's not forget reliability. HUGE thumbs up for this video And well i cant say it enough, your skill set just shines in this video THANK YOU yet again keep them coming!! Oh one last thing. I just want to say thank you again for taking the time to share your methods insights and to show us all how it is possible to do repairs without a bunch of special tools lol. Like a hotrod lol so much can be done with a hammer screw driver and a vaccum gauge if you know what you are doing !!

[@UncleDoug]

Thanks for all the great comments, B2. Have a wonderful Christmas :)

[@Route66Wanderer]

Always a joy to sit back with a glass of fine spirits and enjoy your dissection, analysis, and repair of a classic amp from the annals of musical history! Cheers and Merry Christmas Uncle Doug.

[@UncleDoug]

Thanks so much, Wayne. Have a wonderful Christmas :)

[@Schwaadrumz]

Glad to see you back on here. Missed you. Hope all is well, thanks for sharing your always informative and entertaining stuff!

[@UncleDoug]

Thanks, Manfred :)

[@jonpardue]

Really interesting and thorough repair video Uncle Doug! Thanks for taking so much time to explain every detail, made it easy to follow along and understand on a schematic here.

[@UncleDoug]

Glad you enjoyed it, Jon :)

[@uptownphotography]

Very interesting video and interesting hybrid wiring. Great to have those schematics to compare the two... Phil

[@UncleDoug]

Glad you enjoyed it, Phil.

[@uptownphotography]

@@UncleDoug Thanks Doug. I actually have to watch the second half as I had to run out suddenly (my two rescue dogs insisted on a walk!), so I am looking forward to the 2nd half this afternoon. All your videos I find very well done and enjoyable to watch... Phil

[@UncleDoug]

@@uptownphotography Glad to hear it, Phil. Have a good walk.

[@GL64]

Great work Mr Doug!

[@UncleDoug]

Glad you liked it, GL :)

[@mozilla2576]

Great work Doug! Really enjoyed you brain storming all those issues out loud. Can't wait for the next video. Happy Holidays in 23/24!

[@UncleDoug]

Thanks, Mo. Glad you enjoyed it. Likewise on the good wishes.

[@stevenclarke5606]

Hi uncle Doug, another great job, it turned out to be quite a lot of work, very impressed. Top marks to the Euro probe’s people exceptional customer service .

[@UncleDoug]

Thanks, Steven. Agreed re Eurotubes :)

[@davidsigglekow1349]

Your troubleshooting abilities without using troubleshooting equipment is astounding!

[@UncleDoug]

I'm basically a mechanic and I (try to) approach each job from a common sense perspective. Generally it works ;)

[@davidsigglekow1349]

You’re one of the finest in the business sir!

[@UncleDoug]

@@davidsigglekow1349 Thanks so much, David :)