Marshall Valvestate

[Valvehead]

Looking for some pointers here guys --

Valvestate S80 model 8240

Amp seems to have plenty of output volume , but both channels have weak signal , and lots of hiss . I can hear the guitar faintly . All switches and pots are working.

Ive pulled the pcb and re flowed any crappy joints , new input jack , chop-sticked everything , swapped the 12ax7 , cleaned all jacks / pots ---nothing has helped yet .


Heres a possible clue = in crunch / OD modes on both channels--none of the 4 clipping LED's light up when playing . Is my signal getting killed before those ??

IC 2 /3 /4 all have +11.8vdc/ - 11.8vdc at them

[g1]

IC2 is common to both channels and before those clip LED's.

[Valvehead]

would a TLO 81 or 82 work there? Asking because i have several new ones in my parts bin

[Jon Snell]

A TL082 is a less popular version of a TL072 which has a FET input stage compared to a 3558.
There should be +-12v on the output of the two regulators. Not critical though as long as the rails are fairly clean. The TL072/082 will work at +-8volts without issues.
It is not usual for an op amp to go low gain. I would suspect C1/R2 or the input socket firstly.

[Enzo]

MY first reaction would be the signal is not even reaching the circuits. APply some steady signal to the input and follow it through the circuits. Don't just throw parts at it.

[Valvehead]

MY first reaction would be the signal is not even reaching the circuits. APply some steady signal to the input and follow it through the circuits. Don't just throw parts at it.

I did that and found the problem . IC2 was bad . Amp works perfect now. Thanks guys