Nice coverage on this repair and very well explained. I found this especially interesting because just tonight I was at my bench setting the bias for a Fender AB763 circuit vibrato channel with reverb but no tremelo. I have 6L6WGB's however, and just a little scared about the 455vdc on the plates but, they are NOS Phiilips and have a reputation for handling that voltage quite well. Thats a pretty nifty capacitor tester you have there, would be a nice thing to have in the shop. Thanks for the well done video! NIce work.
I love the sound of these. So crisp and punchy but also still sweet. By far my favourite era of Fender Twins. I have no idea why people hate on them. They're fantastic.
I feel the same way. A couple of tweaks here and there and they are just wonderful. The last one I did was for a studio session and it really had "The Sound". Worked out really well.
Hello Leonard, I finally started the works at my 79 twin, but I am hesitating about the adjustable bias mod. In your video , you replaced the 33K resistor by a 20K trimmer + 15K resistor. I was more thinking of making the 2.2K at the other wiper of the tube matching pot variable. I am curious to know why you choosed the replacement of the 33K. And what is your opinion about my idea of making the 2.2K adjustable. Thank you in advance!
Just finished a 1980 Twin. All I had was the chassis and reverb tank. I found the amp had lost its bias at some point (the bias diode next to the bridge had physically broken, one lead broke right at the anode, I almost didn't see it). That led to red-plating and a lot of damage to the output tube sockets, grid resistors, etc. Transformers survived. I checked/tested everything from the power plug to the speaker jacks. Only replaced what needed it (and that was all electrolytics and OOT resistors). I had to find a cab, the faceplate is rough, the amp has had a rough life so I found a rough cab, a 1966. Getting the holes drilled in the right places on top was a pain, as you know the bolts are short and don't go all the way through on these late 70s amps. Had to reglue/clamp the cab, new baffle, saved the tattered grille cloth. Set and balanced the bias with a set of bias probes into a dummy load/scope. Tight squeeze getting the chassis back in. I had a pair of Celestion G12-65s so in they went. This amp sounds glorious, great for pedals. Thank goodness the cab came with casters!
@@SteverRob Sounds like it fought you until you showed it who the boss was. Good job. There is something about those amplifiers that is just different in a very good way.
Hi Bob I used F&T 220uf 300vdc caps and F&T 22uf 500vdc Caps. for the filters they work really good and are only slightly over rated which is fine. Got them from Tube Depot.
Good morning ! Great work. I'm about to fix my 1979 master volume twin reverb. It works pretty well apart from the chanel vibrato. In fact, I have a fuzzy distortion that appears behind the play notes. I will start with all the modifications you have made to avoid as many problems as possible. I have a question regarding filter capacitor values. What values do you use for example instead of the 70 mfd which does not exist in F&T. I imagined 20uf > 22uF 70uf > 100uF 25uF>22uf 5uF>10uF Do you think these replacement values will work? Thank you very much Rom
This was the capacitor order for the amp: Here is the list: 2 of these F&T axial 220uf/300V 2 of these F&T axial 100uf/100V 3 of these F&T axial 22uf/500V 6 of these Sprague Atom axial 25uf/25V Hope this helps.
Hi leonard, I happen toown a Music Man twin from the same time period. Just getting ready to use again. So I started her up let her warm up, and man she sounds great. So If i wanted to get my MM twin updated, where would I start, i'm in NY?
@@fubopnation8624 So I am assuming it is either a 2475-65 or a 2275-65. I would start by replacing the power supply capacitors (C42,C43,C44,and C45). You might also want to check the 6CA7/EL34 output tubes to make sure they're up to snuff. There is another set of capacitors in the power supply section that supply low voltage (C46 and C47 possibly C31 and C32 as well). It would be good to make sure they are in good shape. Outside of those suggestions I would have to have it in front of me. The Celestion speakers would be a nice touch.
the distortion sounded great, what drive pedal did you use? I have a modded 78 that's kinda a mystery to me, the master pullpot overdrive is high gain (not sure if that's part of the mods in it) sounds great but isn't quite as tight as yours sounded.
I was using a ARC Klone V2. It is an imitation of the Klon Centaur overdrive pedal. I must say it is a great imitation. I had the vibrato channel volume at 3 1/2 and the master pushed in at 3 1/2. The Celestion speakers are really a nice addition to that amplifier.
Awesome job! I have this exact amp on my bench right now. It's been slow going. It had some strange mods done when I got it home. I've been working to restore it to normal operation. I'm almost there. I'm getting about a 4 mA difference in current between V7/V8 and V9/V10. Someone tried to convert the "Output Tubes Matching" pot to a bias adjust pot. It looks like your amp has the original "Output Tubes Matching" pot wired per the schematic? Then you just added a 15k resistor & trim pot? My "bias" adjustment does seem to work, it just seems a little weird. Based on the other hacking that was done in this chassis, I don't trust what I've got 100%.
It's tough when someone has been in there mucking about. You can usually tell when the pairs are way out of match because the hum is substantial. But 4 ma doesn't sound terribly far off.
Absolutely great video. One question. Did you have the huge current draw Uncle Doug did at normal operation? I recall his current limiting light was very bright even when normal. Also, I think this is one of the best ever pedal platform amps. Whomever says they do not take pedals well doesn't play with a lot of pedals.
The power supply handling 4 6l6GC tubes does draw plenty. I think just the way it is for a 135 watt rms amp. The heater current alone for 10 tubes is quite a bit. But it is a heck of allot more then say a 59 Fender Deluxe with 2 6v6gt's. But very similar to a 100 watt Marshall. I couldn't agree more with the your pedal comment.
Hello leonard- i also inherited a silverface twin- master volume- very much molested-i have been going thru it for years-looks alot like this one-Do you have proper prints for this? I am have a hard time finding correct info-- trying to find filter cap resistor values -
I'm not uncomfortable with them but I still get bit once in a while... always obeying the one hand rule. A Leslie amp got me two days ago cause I had to test it live... because of a switching problem... but it was only the second time I got bit this year. Just a little glance and 330v in my pinkie... and lots of cursing... but I didn’t even pause... just kept working and cursing. Lol
One of the worst I ever got was from a Leslie. Wired the 6 pin plug wrong, looking from the front of the plug instead of the back or vice-versa. Left the filters un-grounded and got it all. It really hurt.
@@leonardpeters3266 yea! That was the thing... it wasn’t a terrible shock... just like sticking my pinkie in a blender and pulsing it once! Last year there was a touring band with a heavily molded Hammond A100 and I was checking it out as they were getting no sound... I looked in and the chassis on those is upside down and I could see the tube dangling on the pigtail that held the B+ and sent it to the leslie 122 switching network. He said it was off... because he hadn't turned it on. But he didn't know that the power toggle was switched on from the last gig... but it appears as off because you have to crank the helper motor to get it up to speed and switch on the synchronous ac motor... so I still do it right I use my one hand and kneel down to put that tube in... but it's summer and I'm sweating a lot and as I kneel down I establish a damn good ground and I didn't even get to stick my hand in thank God because as I was kneeling my hand brushed against the chassis and stuck to it... 550v... and I couldn't believe it... how the fuck... and I was falling into the damned thing because of my angle... and I hit the floor, but my hand is still stuck... I figure I'm dead... but I can still move one leg... and I kick the thing so hard it falls over.. and I screamed at the poor guy for ten minutes... left and never went back. That was my lucky one.
Hello Leonard, I have a problem with an amplifier just like yours, I think I have feedback on the reverb and it beeps when I upload it, it's driving me crazy... I would like to contact you by email or messenger so that I can send you a video in case you can help me, I write to you from Spain Congratulations for your video and sharing Thank you very much and I look forward to your response
