Trouble with my Peavey Classic 30...suggestions?

[kate033]

Hey guys,
I have a Peavey Classic 30. It's a few years old, all stock, and has been going strong until last night.

The overdrive channel no longer overdrives. The first channel sounds same as always, but when I switch to the overdrive channel it now sounds exactly the same as the first. The pre knob still controls the volume, but the post knob when cranked, instead of adding gain (and slightly increasing volume) just slighty increases volume. I can still get a nice overdrive by cranking the volume to ear splitting levels, but my neighbors won't apppreciate that!

The 3 Sovtek 12ax7's do NOT light up/glow at all when the amp is on. I've checked in complete darkness. The 4 el84's look fine.
It seemed too much of a coincidence that all three would go out at the same exact time. I've read that they are wired in series, so if one goes they all go?

Could a bad tube be the only problem? Could it be a bad fuse, jumper wire, cap, resistor, etc....?
Anyone have any ideas? I'm guessing it's a problem with the second preamp tube or some component in that area? I'd like to have a go at fixing it, or at least have a general idea of the problem before racking up a bill with a local repair shop.
Thanks guys!

[tubeswell]

Hi Kate - and welcome to the forum.

Just because you can't see the pre-amp heaters glowing, doesn't mean that they aren't working. While all heaters are equal, some heaters glow more equally than others (). The pre-amp heaters in a Classic 30 are wired in series, and if one of the tubes wasn't heating up, then none of them would - so if you are getting 'normal' sound out of the amp's 'clean' channel, then the pre-amp heaters will be working.

For first checks:

1) have you tried swapping the pre-amp tubes around to see what happens? Could just be a bad tube.

2) Is the 'channel' switch-button on the control panel pushed in when you are using the footswitch? If the button is 'off' it overrides the footswitch.

If non of the above apply, then you probably have something wrong with the circuit and it needs a tech.

[kate033]

Thank you!
To answer your questions -

I do not have a footswitch for the amp. I got it used about a year back and it did not have one. So, that's not an issue.

The tubes do still get hot, I just cannot see any glow coming from them like the power tubes. I don't know if if they ever glowed before though. I never bothered to look until it stopped working! They all look the same. One does not stand out from the rest as looking suspicious or "blown".
I have not tried switching them around. I also thought it might be helpful to use a little contact cleaner? I dont' have any at the house though.
I will go try switching them around and see if it makes any difference!

[tubeswell]

I do not have a footswitch for the amp. I got it used about a year back and it did not have one. So, that's not an issue.

That rules that out

I also thought it might be helpful to use a little contact cleaner?

No I wouldn't do that. Just try a tube swap first and report back

[tekhed7]

The 3 peamp tubes' filaments are indeed in series off a -36VDC supply line from the power supply.
But if they were "all out", you wouldn't get poop from the speaker.
One question I have is- what type of "Sovtek 12AX7"? They aren't "EH" tubes, are they? (ElectroHarmonix) Those pcs of crap should be banned form the marketplace as they don't properly incandesce until you get ~8 volts across 'em (pin9 to 4/5).
Assuming you have 12AX7WA or 12AX7WB's, first switch out V2. V2 is the preamp O.D. section. If the channels seem to work properly it was "just a tube". You might want to check the 100K plate resistor off pin 6 of V2 (unplug & let Hi-V drain first, please!) as that sometimes goes hi or open. Also check the pre & post vol pots (VR2 & esp. VR3) for the O.D. channel. A crack at the base can cause issues like this.
The only other component I can think that might be having prob's is that ch.-switching relay (K1). It's a miniature 12-volt DPDT signal relay (PV#71322277) that's fed from the same -36VDC line but has a small 1.5Kohm pwr resistor (R46) in series with the coil end going to ground (via the footswitch). That resistor might be off-value (high) & not allowing the contacts to switch properly. Good luck!

[kate033]

I just swapped the tubes around. Didn't make one bit of difference. I'm starting to doubt the tubes are bad, although I was hoping that was all it was. They do look normal, and get hot.
Considering I'm getting tone, just not the normal one I thought the problem should be the second pre amp tube, since that's the one that gets switched into the gain circuit? I suppose I need to open up the amp and have a look. It must be something in that general circuit? What do you think?

[tubeswell]

Okay so its not one of the tubes. How much work have you done on tube amps?

[kate033]

The tubes are labelled "12ax7LPS Sovtek Made in Russia 99 11".

Thank you for the wealth of information! You've given me a starting point here that I can work through and eliminate possibilites until I find the culprit. Thanks!!! I'll have to open the amp up and start checking.

[tekhed7]

kate- Check my thread off the orig ? mark

[kate033]

I've done a few kits and mods. The basics. I'm not skilled enough to be a tech or diagnose problems, but given instructions or a schematic I can carefully/safely/slowly work out the problem, and I know when I'm in over my head and need to bring it to a tech! Lol

[kate033]

kate- Check my thread off the orig ? mark

I did - reply is below (or above!?) ...Sorry, still getting used to the layout of the forum and hitting reply/quote in the right places!

[tubeswell]

Hi Kate

Be careful in there - tube amps (even ones that are switched off) can contain lethal residual static charges, and unless you know how to safely discharge the filter caps, you probably shouldn't be poking around inside. Besides that the Classic 30 design (with its numerous PC boards jumpered together and crammed into the chassis) is a real PITA to work on and it is easy to break the little jumper leads when you are wriggling the boards in and out, and get more frustrated. If you've never worked on a tube amp before you might be wiser to take it to a tech. JM2CW

(Edit - okay I just saw your reply to the other 'thread'. Layout and schematic attached FYI. My comments about the C30 layout still apply. The 1st thing I would look for is a bad solder joint or loose jumper lead between the boards)

[kate033]

Hi Kate

Be careful in there - tube amps (even ones that are switched off) can contain lethal residual static charges, and unless you know how to safely discharge the filter caps, you probably shouldn't be poking around inside. Besides that the Classic 30 design (with its numerous PC boards jumpered together and crammed into the chassis) is a real PITA to work on and it is easy to break the little jumper leads when you are wriggling the boards in and out, and get more frustrated. If you've never worked on a tube amp before you might be wiser to take it to a tech. JM2CW

Thank you for the warning. I'm not one to get in over my head, so taking it to a tech is definitely something I am seriously considering. Just have to find one in my area.
To be honest, It's reassuring to me to at least have an idea of what is wrong before taking it in for a repair. Kind of like taking a car to a mechanic. I don't want to bring the car in with a flat tire and have them change the transmission while they're at it!
Thank you for the help!

[tubeswell]

Hi Kate, In editing my last post just now, I attached the schematic and layout which would help if you were keen. Be warned, I've worked on my Classic 30 numerous times and one unforgettable weekend, I had pulled it apart and put if back together 13 times over a period of 2 days before I found all the jumper leads were bad or went bad because of all the jiggery pokery. Can be quite frustrating

[kate033]

[QUOTE=tubeswell;118511]Hi Kate, In editing my last post just now, I attached the schematic and layout which would help if you were keen. Be warned, I've worked on my Classic 30 numerous times and one unforgettable weekend, I had pulled it apart and put if back together 13 times over a period of 2 days before I found all the jumper leads were bad or went bad because of all the jiggery pokery. Can be quite frustrating[/QUOTe


Thank you for the additional schematics and info. I really appreciate all your help. After work tonight I'm going to take a close look at the schematics and the amp, and if for any reason I feel the least bit uncomfortable (which may be likely!) I'll take it right to a tech. At least I know what I'm dealing with whether I fix it myself, or have to have it repaired!