Peavey Classic 30

[OMguy]

Hi everyone, I need some help on a Classic 30 that has an intermittant crackling noise. If it warms up after about 10mins it will go away.

Here is what I have done so far:
1) Took it all apart (removing the reverb tank out of circuit) soldered all tube sockets, all jumper wires,cleaning and reinspecting them (paying close attention to the ribbon cable),and all jacks and plastic plugs. ----------Still a noise after reassembly!

2) Subbed 12ax7 (one at a time) no change, subbed el84 (one at a time) no change!

3) Took apart and took out CR4 and CR6, reassembled ---- no change

4) Put an open guitar cord in the return jack and the tone of the noise changed but still there!

5) Took apart replaced C33 R41 R47 and R48 reassembled ----- no change

6) Took apart (now fearing the board interconnecting pins are getting stressed) replaced R42 C36 C53 and C54 reassembled ---- No noise!!! Put everything back in cabinet and checked the next day and after 1min it started cracking again ------(Hang on a minute I need something to drink ----- mouth is dry talking to myself).

Has anyone out there had noise problems on this unit that they have found. I need to give it one more shot, but I think the owner wants it back to use! I have tried to read as many Classic 30 threads as I could find, but maybe I missed some! Thank in advance -----------------OMguy


Tried to attach a copy of drawing to mark on. Not the best but I tried to yellow in the parts I have replaced. I get on the forum from time to time so I am slow on responces sometimes, I apologize in advance!

[hrbay]

Sounds like a dirty socket. Rock the tubes in their sockets once it heats up to see if it misbehaves as cold. Probably preamp?

[OMguy]

Thanks hrbay, there are a couple of things I forgot to post (I must be getting forgetful!)

I removed the phase inverter 12ax7 and did not get any noise (with the 4 - EL84's in)

I did tap and wiggle all tubes while it was running ----- no change

My friend guitaraddict was over and he said he could here a very slight whistle (harmonic) while hitting a low E on a guitar ( it sort of sounds like a tea kettle! (after that I made him some coffee!!!) strange problem and I am not that experienced with that type of noise!

[Gtr_tech]

Replace the plate load resistors. Crackling is a common symptom when they start to go south. 1w metal films are usually a good choice for these.

[Enzo]

And pulling the PI tube won;t tell you much, since it also then disables the preamp tubes.

[OMguy]

Thanks hrbay, Gtr_tech and Enzo, I work on these for hobby so sorry about the slow replys!!! I just took it apart again and I have replaced R1,R2,R3,R4,& R54 per Gtr_tech' suggestion. I realize the three preamp tubes are in the -36v series line. Would that tell us that the EL84 are not causing it? I am not sure but that is why I tried it. The unit is very clean and I also took a cotton tip and 99% alcohol to clean down between the pins. I noticed that the pins had a very slight (must be high temp high dielectic) grease in the pins (I tried to leave some of that in the pins yet!). I hate to shot gun the board but I fear the constant removal of the board will stress the interconnect pins. I am hoping for suggestions on what other people have seen on this chassis. I am almost tempted to make a frame and extender cables to be able to run in a position to test it!!! I do not know how long the person who owns it will let me mess with it! Your feelings on replacing bypass caps or electrolytics? What would you do?

[Amp Kat]

I would try to figure out whether it's a preamp or poweramp problem. Take the send out to another amps return. Still crackling ? You know it's at the preamp then take the preamp of another amp to the retuen of the C-30. If it's still there it is likely the filter caps as that is a symptom of bad caps. If it's not in the output you know it's likely in the preamp and it could be several things. Loose jumper wire,caps are cold solder joint.

[OMguy]

Thanks Amp Kat, I will try to do that! I was able to unhook the power and output transformer wires from a retaining clip in the back, and stretch them over to plug in while the chassis is out of the frame! I thank everyone for their advice!------------OMguy

[Enzo]

Do you mean the circuit board out of the chassis?

If you plan to operate the circuit board while not mounted in the chassis, get out some clip wires. There are various points in the circuit that are grounded by the jacks to the chassis. When the boards are out, there willl be missing grounds. I expect to have to clip some of the jacks to chassis for it not to hum like mad.

[OMguy]

Hello Enzo,I noticed that you replied to me at 10pm and another person at 2:33am (when do you sleep!!!). I was able to operate this chassis out of it's frame and the good news is the chassis did not have any excess noise due to grounding points. I may have gotten lucky and possibly found the bad part! Take a look at the schematic, I was able to get a meter on the chassis and when I finally hit the point between C6 and C52 it showed 1volt sometimes down to .68v while I could get it to crackle and pop! I replaced C6 and after that no noise (which I have experienced before but noise showed up after I put it back into the chassis) and the voltage as the tube heated up was -1.13v and .08v after warmup. I will try the amp again tomorrow and give a reply. That way I can see if it makes noise after sitting for a day! Thank you for your feedback everything helps for I was not sure what move to make next. -----------------------OMguy

[OMguy]

Hi everyone, I tried it today from a one day cold start and no noise but the voltage at C6 and C52 junction went to .9v and floated down to .7v but no noise! Well back into the frame and I will test it later. All for now -------------OMguy

[OMguy]

Hi everyone, I just realized I have been calling the circuit board the chassis, sorry! Well I have got everything back together, turned it on today and no noise! Thanks to everybody for the help! -----------------OMguy.