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112-65-RP Low pre-amp volume

Hello all,

I have a '78 12-65-RP that was brought to me by a friend. It was sitting in storage for many years because of a reverb problem.
I repaired the reverb issue and tested the amp out. It was acting strange, going from clean to distorted seemingly on its own and all the pots were scratchy. At this point I recapped with all new electrolytic's, replaces the 16v and bias diodes, cleaned all the pots and jacks, cleaned the tube sockets, removed the "death cap" and corrected the power/fuse/switch wiring, biased the output transistors, and roled the 1458s through the different sockets, and rolled a new 1458 in all sockets, tested all resistors in place for open/shorts.

I am now left with a very weak first gain stage. I have plenty of gain if i use the mvolt input, but not if i use the High or low gain jack. Using the input jacks, the output is just a little louder then the acoustic volume of the electric guitar, with both gain and volume on 10! What am I missing?

Full Name
Patrick Mulrooney

Member for

5 years 2 months

Mulmany Mon, 03/09/2020 - 12:04

Forgot to mention that my +-16v rail is still fluctuating even after the recap and diode replacement. It fluctuates about 1.5v.

Full Name
Patrick Mulrooney

Member for

5 years 2 months

Mulmany Fri, 03/13/2020 - 20:41

Here are some pictures of what I have done, and the original. Still trying to work out what's causing the issue. All my voltages seem to be with in the ranges that I have found on this forum. I am also getting distortion on the input if I put my signal gen on the inputs of the first 2 opamps.

112-RP-65 https://imgur.com/a/1a8Wio7

Full Name
Frank DeSalvo
Music Man Equipment
1974 130HD

Member for

5 years 2 months

Luthier Vandros Tue, 03/17/2020 - 00:10

In reply to by Mulmany

I’m in the same boat, but it is only channel 2 of a 74 130 HD. I’ve done all electrolytics and even replaced opamps 3&4. Stumped.

Full Name
Charles Carter
Music Man Equipment
Music Man 212 HD 130 (pre-1979)

Fender Twin Reverb Silverface 1979

Fender AVRI '62 Jazzmaster
Partscaster
Squier Vintage Modified Jaguar

Member for

6 years 5 months

greatlakesurf Fri, 03/20/2020 - 20:53

Is it a bad capacitor somewhere? Luthier Vandross had success changing a .1mfd capacitor near IC-3. From the look of your picture, those capacitors look pretty new... Just wanted to chime in with an idea and wish you good luck!

Full Name
Charles Carter
Music Man Equipment
Music Man 212 HD 130 (pre-1979)

Fender Twin Reverb Silverface 1979

Fender AVRI '62 Jazzmaster
Partscaster
Squier Vintage Modified Jaguar

Member for

6 years 5 months

greatlakesurf Fri, 03/20/2020 - 20:53

Is it a bad capacitor somewhere? Luthier Vandross had success changing a .1mfd capacitor near IC-3. From the look of your picture, those capacitors look pretty new... Just wanted to chime in with an idea and wish you good luck!

Full Name
Patrick Mulrooney

Member for

5 years 2 months

Mulmany Sat, 03/21/2020 - 08:15

In reply to by greatlakesurf

Thanks!