The amp sounds great (other then the squeal) Could the 2 power transistors SJ6392 be bad causing the squeal?  FYI I changed the 2 power transistors. Exactly the same squeal at the exact settings.

Notes to myself: After replacing the IC3, the input jack, 4 small 2.2mf caps, tested a new reverb pan and resoldering the 4-pin reverb-connector base on the main cuircuit board...the squeel has shifted but still there at high volumes when I turn up the "saturation" pot.  I don't have a reason yet for the burnt c66 22 ohm 1 watt resister that I replaced.  Going to look at that curcuit today for an excessive current or voltage drop.

Quote from: mikeskory on November 29, 2017, 02:24:34 PM
Hey Enzo,

Yes I have popped in a new U3 4558. No change. I just checked the Pin 1 and Pin 7 and YES when the oscillation kicks in, I see it at Pin 1 & 7 immediatly.  Here's another curious thing which I thouight was irrellivent but 22 ohm 1 watt resister R66 is obviously burn from over heating. It tests ok in curcuit cold. Maybe I should run over and get one fron Fultons before we go any further...

PS the reverb pan is Type 247 and appears to be stock. I ordered a new pan#4EB2C1B. That will solve the hum or eliminate that as the cause. I need a know good pan in stock anyway.

Hey Enzo,

Yes I have popped in a new U3 4558. No change. I just checked the Pin 1 and Pin 7 and YES when the oscillation kicks in, I see it at Pin 1 & 7 immediatly.  Here's another curious thing which I thouight was irrellivent but 22 ohm 1 watt resister R66 is obviously burn from over heating. It tests ok in curcuit cold. Maybe I should run over and get one fron Fultons before we go any further...

Hi Enzo!

BTW I'm still waiting for the transistors for the Pizza Party amp. Will call when all in.

Enzo sez: Turn the reverb down, but scope the output of the reverb IC, U3 pin 1.  Is the oscillation still there?  Also scope pin 7, is it there too or either?
Mike sez: OK will try that tomorrow

Enzo sez: Does the reverb control affect the frequency at all?  Does the post control affect the frequency?
Mike sez: yes for sure. If reverb is off then post works fine. If post off then the reverb control won't trigger the squeal. When reverb is unplugged no squeal.

Make sure the correct pan type is used - 4EB2C1B.  It must have the input jack insulated from the pan.
Mike sez: I'll check that tomorrow.

Enzo sez: And does unplugging the reverb pan stop this or not? \
Mike sez: Unplugging reverb stops the squeal

Enzo sez: Pop a different 4558 into the socket at U3, to see if there is any crosstalk in the IC.
Mike sez; I have already done this.

https://www.ssguitar.com/index.php?topic=2279.0Peavey Studio Pro 40 with a bad squeel. It seems to be hinged to the reverb section. With everything in it's place, the amp will squeel when the reverb is past 1/2 and the "Post Gain" is past 1/2. Input signal or not.  I was courius if this old post was ever solved but I decided to start a new post.

This is the exact problem I'm hearing on a customer use is the year 2017. Did you get this fixed?

Yes it appeared to solve the problem.  I installed the power caps and rechecked the sine wave for.m.  It looked good so I delevered it.  Cusromer picked it up last week.  So I think we got got.  THANK YOU

The adjustment worked exactly like you said.  Not a lot of leeway but I found the exact spot.  The customer wanted new power caps so as soon as they are in I'll check the alignment again before we call the customer.  I'll let you know how it goes.

I see.  one picture at a time.  Here's the middle one

Shots 2 and 3 from the output of the Crate PA8.  as the input signal is increased

Here is the 1st of 3 scope wave shots at output of Crate

With 300 htz going into the 1/4 inch I have a complicated signal at the speaker out put.  Basically its 2 sine waves crossing.  As I turn up the input signal (at the generator) it goes into 1 wave but with distortion.  I'll post up some pictures...

Honestly I'm gun-shy about putting my scope on the audio outputs.  Maybe this is a good time to talk about that.  The bench has a new 'isolation transformer' for my signal generator and scope.  Should I test the audio output with my ground on the circuit board ground and the probe at the positive speaker term OR use the scope right across the speaker terminals.

#1 yes I tried different speakers.
#2Used a scope from the mixer stage on pin 5 of the 5 pin connector called JL.  With 300 htz into the phone jack the wave looks good.
#3Checked voltage at this same connector. Schemo says 16 v.  I'm getting 17.5 neg & pos.
#4 Checked voltage at IC1 16 + 15.8 -
#5 The sine wave out of the IC101 pin #1 (TP1) looks terrible. Flattens out on the top and bottom.  FYI The unit is plenty loud!
#6 I'm way older then you