Marshall Artist, extremely low volume output.

[mfreqmaster]

Hi, I have an old 80s Marshall Artist, 30 watts, 2 EL34s. The amp had worked fine for a number of months but now it has a super low output. I have determined the preamp section works fine because I ran the effects send to another amp. Both channels operated as they should. I substituted the phase inverter and the power tubes from another working amp and the problem persists. Here are the voltages from the power tubes:
V2 V3
P3 488V 489V
P4 486V 487V
P5 -49V -49V
P6 488V 488V

Any assistance would be appreciated.

[Randall]

Have you tried a cable between FX send and return?

[mfreqmaster]

Yes. Doesn't change anything.

[m1989jmp]

Anyone else think that bias voltage on pin 5 is a bit too negative for EL34's?

[alexradium]

Hi, I have an old 80s Marshall Artist, 30 watts, 2 EL34s. The amp had worked fine for a number of months but now it has a super low output. I have determined the preamp section works fine because I ran the effects send to another amp. Both channels operated as they should. I substituted the phase inverter and the power tubes from another working amp and the problem persists. Here are the voltages from the power tubes:
V2 V3
P3 488V 489V
P4 486V 487V
P5 -49V -49V
P6 488V 488V

Any assistance would be appreciated.

please report also the PI tube voltages
you also have a couple of opamps in line from the return jack to the tube,it could be some failure or simply a fractured soldering.

[alexradium]

Anyone else think that bias voltage on pin 5 is a bit too negative for EL34's?

i'd say to turn off an el34 you must go up to -80V

[mfreqmaster]

PI voltages: p1 434v, p2 7v, p3 31.5v, p6 221v, p7 18.5v, p8 31.5v

[alexradium]

PI voltages: p1 434v, p2 7v, p3 31.5v, p6 221v, p7 18.5v, p8 31.5v

The resistor connected to pin 1 is most probably shorted,once replaced the voltage will be similar to pin 6

[mfreqmaster]

I suspected that too, but measured and it is 87k ohms. I will check the solder joint to that pin next.

[alexradium]

I suspected that too, but measured and it is 87k ohms. I will check the solder joint to that pin next.

reflow also pin3

[g1]

Are both sides heater lit at PI tube position?

[Enzo]

I'm with g1, it is most likely the pin 1 side of the tube is not conducting, usually because the heater is not lit.

I have never in my life seen a shorted resistor.

[The Dude]

......I have never in my life seen a shorted resistor.

Ditto!

[g1]

Me three. Although I did see one once that had decreased substantially in resistance. So I never say never about that anymore.
Although I still never expect to see a complete short.

[The Dude]

The only time I've come close was when I measured a 100K resistor and it measured 10K. It was while teching at a manufacturing facility. After encountering the same part problem several times, we checked the batch. It turns out the manufacturer marked a batch of resistors wrong. Still,...... they didn't short- I don't recall ever seeing a shorted resistor.