Peavey Classic 30 problem

[Smada]

Hi guys, I am new here and have a problem that I hope you can help me with. I have a 1995 Peavey Classic 30 amp which I was getting a volume drop on and a loss of tone. Initially I suspected the tubes but I replaced these and the problem persisted. My next move was to open it up and do the chopstick test. Upon doing this I got a tapping noise from the speaker when I poke pin 7 on the preamp tube in position one (furthest away from the power tubes). I tried putting different tubes in there and the tapping noise still came through, and most recently I have replaced the tube socket but I still get the noise. So now I am a little stumped as to what the problem is, the only thing I can think of is that there is a break in the actual PCB ? I have come here for the opinion of people who know more than me on the subject and I hope you guys can point me in the right direct??

[xtian]

Could be cracked trace, but could be other things: nearby cold solder joints, microphonic coupling cap, cracked grid stopper resistor. Post photo of your repair work?

[g1]

Did you fix the original complaint?
Can you make any issue without the chopstick?
If not, I would think it may be normal. Prodding the grid of the first stage is going to make some noise.

[Smada]

Heres two images of the new socket, one from either side. I also here the tapping sound when I prod the solder joints for the 3 resistors that are connected to pin 7, however I do not get the noise when I tap the solder joints on their other side or when I prod the actual resistor. From that front side image I cannot see any crack in the PCB. I also tried connecting pin 7 and all three resistors in one large blob of solder which I think should (?) have taken any crack underneath out of the equation but the tap still persisted.

If like you say the tap on pin 7 is normal then all this has been in vain, but none of the other preamp tubes make a noise when I prod pin 7 on them. I have not yet put it back together to test since the tapping is still there.

[Enzo]

But your problem was a loss of volume and tone. it is normal for the first tube to be somewhat microphonic.

[Smada]

Hmm interesting, do you think if I check all the pin voltages to see if any are wrong it will clear it up once and for all?

[Enzo]

I think that is one step towards finding out where the problem lies.

[Smada]

Well I will give it a go. Does anyone know where I can find out what the ideal levels should be on each pin for a classic 30? And do I need a guitar plugged into the input for this? Thanks.

[Enzo]

We don't want to find zero on a cathode, and we don't want any plate voltage to equal the B+ supply voltage.

[eschertron]

We don't want to find zero on a cathode, and we don't want any plate voltage to equal the B+ supply voltage.

Has anybody ever called you 'Zenzo'?

[Smada]

Sorry I have not done this before and I am struggling to find good information on it! Am I measuring each pin from ground to pin? And which pins are AC / DC ? Sorry for so many questions.

Also, when I try and measure pin 7 from ground the speaker gives a very loud crack even at very low volumes so that I only dare hold it down for a second. Is that normal?

[Smada]

The plate voltages on the pre amp tubes seem very low, each one is less than a volt. Could there be a problem somewhere in the rectifier stage?

[eschertron]

The plate voltages on the pre amp tubes seem very low, each one is less than a volt. Could there be a problem somewhere in the rectifier stage?

Are you measuring AC or DC? Can you switch your meter between modes?

[Smada]

Yeah I can switch between modes, I was measuring the DC level on the plates for the pre-amps.

[eschertron]

So with the amp on, and out of standby, one meter probe on ground (I always clip it to chassis, easy enough) the other meter probes read low at plates?
What about the PSU voltages? Read the DC voltage at the + terminal on the reservoir cap. Anything there?

Let's take a step back. In post #1 the amp worked, mostly. If you have <1vdc on the preamp plates, the amp would not work. Does the amp work? Are you measuring and reporting the cathode voltages thinking that they are the plates? They could indeed be in the 1 volt range. With the work done on the amp, what if anything has changed? Does it still work?