Oh yes...ANOTHER Tsl Marshall!

[Valvehead]

So i have a 3rd TSL 100 here (in a month) .

This one had an eL34 short and it took out a couple resistors right near it . I believe it was a 1 ohm and a 100 ohm . I pulled the board and cleaned it up and replaced needed parts . Installed new power tubes. Ive worked on this one a couple years ago--so all the solder joints have been fixed. The 1k Screen resistors all test good

So the amp powers up and passes signal , but has very low volume (all channels) .

I cant find anything wrong so far , I have another working Tsl 100 sitting here , so just to eliminate the OT , i clipped in the other one. Same thing - very low volume.

i did run the amp going into the return of a different / good 60w amp and it was plenty loud (fx send to fx return)
Going from the good amp into the fx return of the tsl --low volume.

B+ is 520vdc

Heres something strange=
The bias.
at each el34 , i have 40mv bias on pin 5

But measuring at the bias pins out back , i have 24mv and 2 VOLTS dc
measuring the OT , shunt method , i have 18ma and 12 ma

all 8 tubes have plenty of dc volts to the plates

any ideas ?
i dont think the weird bias readings are part of the volume problem--i could be wrong ??

[tedmich]

Is the schematic here?

Marshall Schematics

[Valvehead]

yes -- the TL10-60-02 matches the main board

r8 and r9 were replaced

[The Dude]

Remove that little bias board and check all of the solder joints.

[Valvehead]

it looks great

[The Dude]

When you subbed in the other OT, did you connect the speaker directly to an output tap, or did you use the existing impedance switch/jack combination that exists in the amp? The reason I ask is because it's not uncommon for there to be problems with the impedance switch and/or switching speaker jacks.

[Valvehead]

used the existing jacks--tried all 3.

i guess i can just swap that whole pcb with the good amp to try it.

[The Dude]

...or just hook a speaker directly to the OT secondary wires to eliminate the possibility of a problem with switch or jacks.

[52 Bill]

Heres something strange=
The bias.
at each el34 , i have 40mv bias on pin 5

But measuring at the bias pins out back , i have 24mv and 2 VOLTS dc
measuring the OT , shunt method , i have 18ma and 12 ma

I don't understand the readings here. There is 40mv dc on all pin 5's? Are the tubes red plating?

R9 is the bias read resistor, did you replace it with the wrong value? That might explain the 2 vdc reading on the bias set jacks.

[The Dude]

Good catch, Bill! I hadn't noticed "pin 5". I assumed those were readings across the cathode resistors. Yes, maybe that 100 ohm you replaced was supposed to be a 1 ohm? Make sure R6&9 are both 1 ohm.

[Valvehead]

swapped the speaker jack boards---no change

[Valvehead]

Bill for the win !

it was a 100 ohm in there, i must have had 1 in my 1-50 ohm parts bin Im headed out for a quick tour so ill order a resistor and get it in there tuesday.

do you think thats my volume problem too?

thanks guys

[Tone Meister]

Bill for the win !

it was a 100 ohm in there, i must have had 1 in my 1-50 ohm parts bin Im headed out for a quick tour so ill order a resistor and get it in there tuesday.

do you think thats my volume problem too?

thanks guys

Reminds me of the time I installed a 470K on one 6L6 socket in a Fender. And yes, most likely you'll get your volume back. I did ...

[Valvehead]

Well boys , i put that resistor in , and that high reading is gone , but im only able to get a max of 38mv and 28mv . Also---super low volume still

[52 Bill]

While perhaps not optimal, the current readings should not be a factor in the volume loss. 15mA per tube should be fine for now.

Do the usual things, check the break jacks, send a signal into the power amp, take a signal out of the preamp, etc. Try and isolate the signal loss to a specific circuit or section of the amp.