Peavey Encore 65 Amp. No Sound?

[Sigala]

Hello,
Trying to troubleshoot a friends Amp that has no sound output.
Checking all the compnents caps, resistors, seem to show no bunrt out components. Tried replacing the tubes, Still no sound.
If you rattle the reverb unit you cam hear low audio of the spring.But nothing for a guitar input?
ANyone have any thoughts on this, and schematics?


Dennis Sigala

[Enzo]

COntact customerservice@peavey.com and ask for the schematic.

And take voltage readings at teh tubes. Is B+ present? DO the heaters ALL light?

[Sigala]

Thanks Enzo
I will contact Peavey for schematic!
I do see the heaters light, but will start taking measurements as soo as I know what pins B+ is and so on!
Thanks very much
Dennis

[Enzo]

And don't forget to check the speaker and its wires.

[Sigala]

Well, I found an open 100K Plate resistor, On V2 pin 1.
Schematic calls out 100k 1Watt, for all these resistors, what actually on the board are 1/4 watt, I call Peavey and tech stated, that they had screwed up, and there should have been 1 Watt resistors. Well I just had 1/4 watt resistor and put that in just to test, It works somewhat, but the 6Lk tube socket I believe is intermittent as the sound is distorted. Plate voltages for V1 through V4 are running, 235v, 205v, 235v, 288v
I suspect the rest of the 100K resistors are the reasons for the Variation in voltage, I plan on replacing all the 100K with 1 Watt.
And re-soldering the tube sockets. The Caps are not bulging or showing any leakage, Should I replace those too?
Thanks for all your help Enzo!
Dennis

[TerryEncore65]

Just a thought have you tried connecting the "pre amp out" jack to the "power amp in" with a regular 1/4" guitar/patch cable? These jacks are used for your effects chain, and sometimes the contacts get a little oxidized and won't pass or pass poorly your signal. Happened to me when I first started using those jacks. You can clean them with contact cleaner or the like. As for the caps, without troubleshooting, If you haven't already done them, I would highly recommend replacing the big electrolytic power supply caps ie the gray ones made by "Illinois Capacitor" I got mine from "Allied Electronics" for a couple or dollars each, made a world of difference, quieted the amp right down. Be mindful of the voltage ratings on the individual caps and make sure you don't try to undersize them. As for the resistors you could possibly replace them all, but unless they're popping left and right IMHO why bother? Just my two cents.
Terry,
a fellow Encore 65 owner

[Sigala]

Hi Terry
Thanks for the info, not sure what you mean with the Pre-Amp out to Amp in
There are 2 jacks on the chassis, Which are marked as such are you saying to plug a patch cable from the pre-amp out to the Amp in jack?
Dennis

[TerryEncore65]

Yep, it's for your effects, fuzz,chorus, etc. Pre amp out to Power amp in. I had a Digitech
rp300a plugged in there for a while, tweaking settings etc. and later, much later Iwas playing at a friends house without the rp300a and the sound got all weird. Also inherited a Bass amp with no sound and after doing some checks on the board and not finding anything conclusive (other than someone had clipped and then resoldered the legs of the output transistor -it was a Fender Sidekick 35 Bass amp) plugged in a patch to the effects out- effects in and Voila! works! I'm not saying this is the problem in your case but my Encore dates back to the mid-80's. P.S. I've heard a "small fan" can help keep it cooler, the pcb is prone to warping due to the heat. I haven't tried it though.

[Sigala]

Hi Terry,
Just paid the man $100.00 for the Amp
So looking forward to getting it all working right.
Going to do a Cap and change out the 100K 1/4 watts with 1 Watt.
And probably re-flow the soldering on the Tube sockets. yes the Peavey tech told me the thin board was prone to warpage, so thats a great idea to add cooling fan, Thanks. I now have to order a bias probe, so I can set the bias.
I have some Sovtek 6L6's and Sovetk 12ax7 tubes to replace the factory ones.
Back to the pre-amp out and in. Should I connect a patch cable from Pre-amp out to Amp in to check what you mentioned?

Dennis

[Enzo]

The amp makes no sound. If the signal cannot get past those jacks, it can;t come out the speaker. SO plug a spare cord from preamp out to the power amp in jack next to it. If this restores sound, then the power amp jack needs service.


Likewise, you can plug the guitar into the power amp jack. Get sound that way? And plug the guitar in out front like always, and run a cord from Preamp Out over to some other amp so you can hear what is there. Got sound from that?

[Sigala]

Hi Enzo
I am getting sound at the speaker, its just distorted, So I believe after replacing the Plate resistors and Caps at the power supply, hopefully the distortion will go away.
And I mentioned replacing all the tubes? Your thoughts. Also I need to re-bias this amp after the mod.

I just tried taking the pre-amp out from the ENcore 65 and plugging into my Nashville 400 and the pre-amp stage is clean, so must be in the power amp section.
Thanks all you folks for helping me out. Any tips on Biasing this Amp, I was going to buy a Bias probe??

Dennis

[Gtr_tech]

Tarnished contacts on the pwr amp in jack can cause distortion, as well as intermittant loss of signal, or complete loss of output. See...there's normally closed contacts in that jack ( the pre out or send is just tapped off the preamp signal, not in series with it), so if signal can't get across those closed contacts, it doesn't make it to the output section. If the contacts get resistive, weird things can happen. When you bridge the loop with a cable, those contacts are out of the equasion since you're doing it manually with a cable.

Bridge that loop with a cable and see what happens. If there's another loop, bridge that too. Some amps have 2 loops. One marked "pwr amp out" and "pre (or main) amp in", and one marked "effects send" and "effects return". They both do the same thing but may be at different points in the signal path.

[Enzo]

Here.

[Sigala]

Thanks everyone for all your help!
I am wanting to change the fixed bias of this amp.
It uses R67 470 ohm Resistor.
I thought of using a trim pot, with a fixed resistor.
trim pot Pin 1, Wiper (pin 2) Pin 3.
connect pin 3 to fixed resistor to where R67 was, then tie wiper pin2 and pin 3 together to the other end where R67 was??

Radio Shack only has 1 K trim pots. so not sure how to do this??
Any help would be appreciated!


Dennis

[Enzo]

That won't work. Changing the 470 ohm resistor to 1k will drop the bias voltage less than a volt. The 470 is there mainly to improve the filter action of the two caps.

The bias voltage starts out with the -57v supply. Unless you rebuild the supply completely, there is no way to increase that.

The bias voltage is slightly lower at -56v, then -55 at the grids. There is a voltage divider formed by the 470 ohm R67, and the 47k R58. The only way to make this adjustable is to increase the 470 to several thousand ohms and make R58 variable.