peavey encore 65

[brett]

Hi all…I have a peavey encore, a 65 watt all tube 2x 6l6 amp (ss recto)
It’s a single channel , but with 2 gain structures ,normal and “pump”
So,  when “pump” is switched on it all works as expected ,  as described in the manual here , all 3 pots in the gain block work ( except the pull smooth switch doesn’t alter the sound)

Link to the manual    http://peavey.com/assets/literature/manuals/80300051.pdf

schematic attached (hopefully)

When the “pump” is off (footswitch) the imput gain alters  the signal,  but post gain doesn’t … it seems to be full on and  pull smooth doesn’t alter the sound . I can't follow how the pump works with the LDRs, I guess the signal is bypassing the post gain pot somewhere that it shouldn't when the pump is switched off

After some vigorous knob twiddling I buggered the carbon track in the post gain / pull smooth pot . I was hoping the problem may have been the pot but after replacing it the amp is just the same . On the plus side it was a good excuse to do the caps.. at least it's quiet now!!

I could just use the pump gain I guess but I hate it when things don’t work right
and I would like a bit more clean control
any help would be greatly appreciated ,Thanks brett 

[PRR]

> When the “pump” is off (footswitch) the imput gain alters  the signal,  but post gain doesn’t … it seems to be full on and  pull smooth doesn’t alter the sound.

That is the way I read the circuit. Pump LED off, LDR2 off, bottom of "Post" pot and "Smooth" switch are disconnected from ground. Load on Post pot is hi-Z, so with pot un-grounded the pot turns 100%-90% of signal, instead of 100%-0% when pot bottom is grounded.

I have not read the manual to see if it says some other thing. Manual writers sometimes get bad info.

If you still suspect fault:

Measure voltages at LEDs and resistances at LDR resistors.

All LDR resistor legs should be at zero voltage (else a cap leaks). One resistance leg is (should be) zero resistance to ground. You can measure resistance at the other terminal with amp powered but silent. Turn "Pump" knob CCW; still this pump pot shunts LDR1 resistances so you won't get a real high reading; but you can tell it is much more than 1K.

LDR LEDs can't be seen so the "bright/dark" is conceptual. By voltage, under 1.5V across the LED is dark, over 1.6V is bright.

Pedal open:
LDR1 dark
LDR1 resistors over 100K
LDR2 and "Pump" bright
LDR2 resistors under 1K
point A at 3.7V

Pedal shorted:
LDR1 bright
LDR1 resistors under 1K
LDR2 and "Pump" dark
LDR2 resistors over 100K
point A at 1.6V

[brett]

Thanks PRR Hmmm ,maybe that is the way its meant to be..although there is the matter of the smooth switch not working at all.. Guess I will have to pull it out and do some measuring . Its hard when you don't know what it should sound  like !!!    Thanks, Brett