New Tubes and disaster

[st220]

Hi, New to this Forum so looking for some serious help!!
I have a Marshall TSL 100 head - model from 2001, symptoms before
i replaced the valves was a very loud background hummm.
As with some of the threads in this Forum i to had the runaway BIAS and that destroyed 2 of my JJ KT77's (cooked them).
I ordered a matched pair & while i was at it i replaced the 4 pre amp tubes
with JJ ECC83S.
After putting this lot in i BIASED the amp at 80mv per side and it appears to be stable even after 30mins off standby.
But....now comes the problem!!
The Clean channel works fine, loads of power & no background humm, the lead and crunch when selected are both DEAD, even at volume 10 only a faint output can be heard through my 1960a cab.
I have resulted in putting all the old tubes back in (the humm comes back), but the problem is exactly the same.
I have tried just about every tip i can find in these threads..
Cleaned & tweaked the valve sockets, checked all the PCB's for O/Heating, all the fuses are intact but still i have no LEAD or CRUNCH channels...anybody in these threads seen this before ?

[Ward]

You need to get in there and have a look. Something is amiss.

[Wilder Amplification]

Hi, New to this Forum so looking for some serious help!!
I have a Marshall TSL 100 head - model from 2001, symptoms before
i replaced the valves was a very loud background hummm.
As with some of the threads in this Forum i to had the runaway BIAS and that destroyed 2 of my JJ KT77's (cooked them).
I ordered a matched pair & while i was at it i replaced the 4 pre amp tubes
with JJ ECC83S.
After putting this lot in i BIASED the amp at 80mv per side and it appears to be stable even after 30mins off standby.
But....now comes the problem!!
The Clean channel works fine, loads of power & no background humm, the lead and crunch when selected are both DEAD, even at volume 10 only a faint output can be heard through my 1960a cab.
I have resulted in putting all the old tubes back in (the humm comes back), but the problem is exactly the same.
I have tried just about every tip i can find in these threads..
Cleaned & tweaked the valve sockets, checked all the PCB's for O/Heating, all the fuses are intact but still i have no LEAD or CRUNCH channels...anybody in these threads seen this before ?

Sounds like something is amiss with the V1a stage in the preamp...not power amp related at all.

While all the other stages in this amp are global (work on every channel/every setting), the V1a side of the first preamp tube is active only when the Ultra Gain channel is selected. I'd try replacing that first preamp tube first and foremost. If it's not that, open her up and look for broken solder joints around the V1 socket.

[st220]

Thanks for the reply...

I have overcome the issue a few weeks ago by replacing the main board with a version 20 supplied from Marshall amplification here in the UK.
Was easier in the end due to the runaway BIAS issue with the version 5 board that i had installed.
For £60.00 it wasn't worth replacing all those heat coefficient resistors etc....
Thanks again for the reply, but just on a last note i can see a hole in the solder joint exactly where you diagnosed the problem.

[CharlieP]

Thanks for the reply...

I have overcome the issue a few weeks ago by replacing the main board with a version 20 supplied from Marshall amplification here in the UK.
Was easier in the end due to the runaway BIAS issue with the version 5 board that i had installed.
For £60.00 it wasn't worth replacing all those heat coefficient resistors etc....
Thanks again for the reply, but just on a last note i can see a hole in the solder joint exactly where you diagnosed the problem.

Resolder and keep for backup!