Recap problem

hossymandias

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 quickly red plating. I'm not sure how to proceed. Any advice?

https://www.thetubestore.com/lib/thetubestore/schematics/MusicMan/Music…

Full Name
John Hostetter
Music Man Equipment
Music Man 212-75
Vox Super Beatle
National Model 90
a million pedal clones

Member for

10 years 6 months

hossymandias Sun, 11/25/2018 - 16:04

One transistor collector was shorted to ground. All is working now. Except my phaser, which didn't work before the recap. Now to dive back in!

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

10 years 9 months

lmv Sun, 11/25/2018 - 16:07

Hi there,

you need to take the amp to a qualified tech. If you took it upon yourself to replace parts without knowing enough about the circuit to troubleshoot it, I respectfully suggest to have somebody else look at it. We can't teach you electronics here, only advise on things particular to the MM amps. Why did you replace the transistors? Did they test bad?

Sincerely,
Lars Verholt

Full Name
John Hostetter
Music Man Equipment
Music Man 212-75
Vox Super Beatle
National Model 90
a million pedal clones

Member for

10 years 6 months

hossymandias Mon, 12/03/2018 - 12:02

Hi Lars,

Thanks for your response and your concern. I should have been more clear about my experience with electronics. I have been working on this amp for many years, have built several amps from scratch and I know how to read schematics, etc. I like posting my problems on here so I can get some feedback and ideas from you all when I get stumped. I think I was premature posting this particular problem since I obviously figured it out pretty quickly. But like I said, thank you for giving me feedback and for providing this resource!