Peavey Encore 65 - need help troubleshooting

[Boy Howdy]

I just got hold of a an Encore 65. It works, but there is a crispy, splatery sort of distortion somewhere in the back half of the amp. I suspect it's the electrolytics. I checked out the preamp with the power amp from another amp and it works fine - no weirdness. So I know the problem is after the preamp out/power amp in.

I haven't heard the sound of failing electrolytics in a long time, and I know there are several different possible sounds it could make. Does this splatery sounding distortion sound like it might be the caps to you guys? It sounds a little like an extreme version of diode distortion, if that helps.

I don't see any visual indications of trouble: bad solder joints, burned connections, etc.

Is it possible that it could be the OT? How can I eliminate that possibility?

Should I just replace all the electrolytics in the back half of the amp (all ... 11 of 'em?!) and hope that fixes the problem?

I have replaced electrolytics before and know about the dangers, but I'm not a proper repair guy.

One other thing: Somebody has been under this hood before. R41, R45, and R53 have been altered. R45 has been replaced (the old one is still in there but with one broken leg). R41 and R53 have the same value resistors paralleling the original resistors for half the original value. Any ideas on why this was done?

I can only find a download only option for the schematic. Sorry, but here it is anyway.
peavey encore 65 schematics - Google Search

[Jazz P Bass]

Peavey Encore 65

Did you try plugging in your guitar in the Pwr Amp In jack.
This jack has a normally closed contact.
If it is corrupt, the signal will not pass properly.
You could also jumper the amp out to amp in with an instrument cable.

[Boy Howdy]

Thanks, JPB. I didn't try going into the power amp in jack. The power amp does work, it just makes that awful noise when I play through it.

I did run out of the pre amp out to another amp's power amp in jack and it works fine that way.


So no opinions on what that bright, splat-ey distortion might be?

[Enzo]

Well, until you do that test, we don;t really know. You say the PA works, but sounds bad. But what we don;t know is if the4 PA itself is sounding bad, or if it is just faithfully amplifying a bad sounding signal.

If the preamp out sounds OK, then th preamp works. Try the guitar into the powr amp in. If that still sounds crappy, then we fix the PA, if however the PA sounds OK that way, then JPBs suggestion of the power amp jack itself being the issue makes sense.

[Boy Howdy]

Ah! Now I get ya. I should learn to read....

Crap! now I gotta put it all back together again. See ya'll Monday.

[Boy Howdy]

Wow, looks like things got busy around here over the weekend.

Well, I put it back together. Didn't really need to, I had already done the recommended test but forgot that I had done it until after I had done it again. Sheesh!

So anyway, I put it back together and couldn't really get enough signal out of the guitar to really hear (or get the amp to make the offending noise), so I did a couple other things: 1) I jumpered the pre in/out jacks with a cable (result: still made the weird distorted sound), and 2) put a different preamp into the Peavey's power amp in jack (result: same weird distortion).

I also tried the amp with a different set of 6L6s. No difference.

Any other ideas, guys?

[Jazz P Bass]

Sounds to me like an output section problem.
You did miss one though.
PreAmp Out to another amp.

[Boy Howdy]

No, I did that (pre out to another amp's pre in). Works fine that way.

I also checked it with different speakers and a different PI tube. It's definitely in the power section somewhere.

[Jazz P Bass]

Output section test

The schematic posted above has a number of voltages listed.
Check them with your meter on volts dc.
Also check the higher voltages with your meter on volts ac to look for abnormal ripple.
This will tell if the main filter caps are healthy or not.

[Boy Howdy]

Thanks, JPB. I'll see if I can figure out how to do that.

[Boy Howdy]

Well, I figured it out, found the problem. The R53 plate resistor was bad. Slapped a new one in there and done. Or so I thought. I was just playing it and the amp appears to distort (in a not altogether unpleasant way, but....) earlier than it should. Like if I hit it hard at very low volume it distorts. It may just be dirt in the pots. I'm out of contact cleaner. I'll have to pick some up and see if that does the trick.

That whole thing with the meter, I've never really used one before, at least not for repair. Glad ya'll pushed me into it. Greatly simplifies the whole process of fixing an amp, huh? Thanks, guys.

[Boy Howdy]

Oh, another thing. Can someone tell me how to do the following? I found this on Harmony-Central.

"This amp does not have factory adjustable bias. The bias (grid) voltage comes from a separate tap on the transformer, and the combination of R67 and R58 set the actual grid voltage. From the factory, Peavey chooses to run the 6L6's very cold. Great for long tube life, but I think the amp can sound much better with a bit more cathode current. I was able to adjust R67 to set a more aggressive bias. For a 25W (max dissipation) output tube, I'm running them at about 70%, with about 35mA cathode current. Sure, the tubes idle at about 15 to 17W, but the amp sounds fantastic."