Tube Amp Archive

This is great feedback. I can fix the strain relief and wire nut no problem.

What other fixes or modifications would you do? Move the 12ax7 socket?

My hope is to use this amp for recording. I'm not interested in volume, but reducing noise and hum is a priority.

Here you go. I was thinking 5f2a as well. The 5f2 has a choke and a tone control. Look like it could be the one. One of the many parts of tube amp operation that I'm still foggy about is the power supply filtering. Does four 33uf filter capacitors seem like overdoing it? Does the KT66 make a differe...

I just picked up a mystery amp from a pawn shop. It is obviously a diy job. It looks like a 5f1 head from a kit, but I can't find any trace of the kit online. The chassis has a faceplate that says "Class of '57" with no other markings. The transformers have no identifiers that I can figure out. I've...

I have owned a Music Man 212-75 for about 20 years and I love it. It was my first tube amp (even though it's "merely" hybrid, I don't care). Somewhere along our journey together, the on-board phaser has stopped working. I've spent the last 5 years trying to figure out what's wrong with it. I've repl...

I got it. One of the new transistors was shorted at the collector. All sorted out now. Thanks guys! BTW, I was able to pull the power tubes and power on no problem.

Hey guys. I just recapped my 212-75. All electrolytics were replaced. The only discrepancies were the two 400mf 25v caps. I replaced one with a 420mf and the other with a 440mf. Also replaced both driver transistors. When I powered her back on, I got nothing but a loud hum. One power tube began quic...

My beloved Musicman 212-75 has been giving me a headache for several months now. It started losing output power so I looked at the service reports and schematics found here: (chassis 2475-75) http://www.music-man.com/techinfo/old-amps.html I tried to bias the transistors and noticed radically differ...

Woohoo! Success! I bypassed the transformer like you said (and it's a good thing you replied because I would have forgotten to reconnect pin 6) and there is tons of spacey, weird reverb that actually doesn't sound ridiculous dialed back to 4-5. Also, the footswitch now works as intended. Now I just ...

Okay, sorry about the long delay. I gave my workbench a makeover and it turned into a huge project. I'm ready to solve this reverb thing finally. So I'm going to accept that my reverb transformer primary is blown and rather than get a replacement I'm going to try to bypass it and go with the transfo...

Also, if I went the transformerless route, what wattage should the added resistor and capacitor be?

Thanks!

Phil_S, when I wrote reverb driver I meant the transformer, not the tank. The tank measures 180 ohms across the input and 162-170 ohms across the output. Pierre, I'm fairly certain the footswitch wiring was okay. I tested to make sure that it shorted pins 2-3 to ground and kill reverb. Now, however ...

I'm considering losing the transformer and running the reverb straight from the tube. What do you all think? I was reading here: http://music-electronics-forum.com/t36664/ Leo Gnardo says: Swap a 10W resistor of 5K to 10K ohms for the transformer primary. Pass the signal off the plate of the drive t...

Thanks for the details, Pierre. I'm thinking I'm at the nothing-to-lose point now, too. I hooked up my record player (unamplified signal straight from the RCA out) to the input of the reverb tank, and with the amp on, turned up the volume and the reverb. All I got was an irregular, scratchy distorte...

Phil_S, lol I thought I had gotten lucky. Don't go through the trouble of checking the turns ratio until I make sure it's necessary to replace it. You are generous enough with your knowledge and advice. Pierre, thank you for the info, I will look at the circuit again this weekend. How did you go abo...

Thanks Phil_S! I'll pm you and try to convince you to part with the non-existent transformer, IF I need it. Hopefull,y I won't need it. I found an old thread in which someone ran their record player through the input of the tank to test the transducer. Let me tell you, I'd much rather replace a tank...