Hi, guys.

I'll get straight to it: I've got a Peavey Classic 50 2x12 from '93 or so and it's having some weird issues.

While it's totally playable, every once in a while, I'll hear some strange noise bursts that seem to stop if I smack the top of the cab (it's a combo, in case you don't know what 2x12 means). I use the amp in 4-cable-method combination with a G9.2tt effects processor. Signal chain is:

Guitar > G9.2tt input > G9 FX Send / PV Normal input > PV FX Send (preamp output ) / G9 FX Return > G9 output / PV FX Return (power amp input)

The clean channel is usually set to 3, lead pre to 4, lead post to 12, and master to 12. This ensures pretty much unity gain in the preamp, except for the cleans being slightly softer than the leads, on purpose. The G9.2tt's master level is set to +4dBm and about 3 o'clock on the dial. Loud, but not driving anything. I mic it on stage, so this is plenty for a small stage with wedge monitors and drums to compete with. At one point I had the G9's send set to 100%, which is 20% higher than unity gain, to drive the clean channel, but I've reduced it to 90% because I started noticing these noise bursts. Once, the amp just started blaring a random tone for no reason, with no input, and switching on standby and back off again seemed to fix the problem.

I bought the thing off a guy as is with the previous owner's tubes in it, and I don't know how long they've been in there. There's a trio of Electro-Harmonix 12AX7s in the pre section (I doubt the V3 is graded correctly) and a quad of Sovtek EL84s in the power section. Being behind a steel grille, I can't see the whole tubes, so I'm not sure if one of the EL84s is glowing oddly, but it's entirely possible they've been abused or used up. I don't remember what the output impedance is on the speakers, but they're plugged in through the factory cable, wired in series. I want to replace them with a full set of JJs, possibly the gold pin 12AX7s and a correctly graded V3 valve, and their EL84s. I'm just not sure if there's anything seriously wrong with the amp.

Another issue I'm having is that the reverb tank doesn't work at all. It's plugged in using the factory cable, but I can't seem to get it out of the factory mounted pouch in the back of the cab. I heard from a friend that you have to tighten the screws on spring reverbs every so often to make sure they keep the right tension, but I'm not sure if that's what's wrong. A possible issue is that the amp doesn't have a solid state, but instead a vacuum tube preamp for the reverb, and the tube is completely dead, or the circuitry fried for some reason. I really have no idea what the problem might be, and therefore no idea where to start.

Anyone have any ideas what I should do? This is literally the only amp I have, but it's a great one and I'd love to get it back in top notch shape. Plus, I'm sure if I use almost any kind of tubes other than what's in it, it'll sound better. I mean, come on, Sovteks, really!?

Cheers!
- Ben Reaves

The reverb is a common weak point on Classic 30/50. It is NOT tube driven, but instead sent and received by separate channels on the same dual channel IC. These are prone to failure because of heat (the chassis on these amps will get pretty stinkin hot).

I've had three Classic 30's, and the first two developed this problem. Luckily, you can get a replacement IC for less than the cost of a postage stamp and it is fairly easy to get to. I've also noticed that the replacements I got were a little more robust than the one installed from the factory.

The part to replace is RC4558P, but from what I understand, you can switch out different values for a stronger or weaker reverb signal. Search the modder forums if you want to open that can of worms.


Also, I'm not sure that you should have the G9.2tt connected in the way that you described. According to the manual, the G9.2tt's FX loop is meant for an external effects unit, not the preamp of the amplifier itself. Try connecting it into the instrument input of the amplifier at '-10db' for a while and see if the problem persists, and then connect the G9.2tt into the effects loop via the normal in/out jacks with the '+4db' setting. One of these solutions should provide the sound you want without the strange noises of the current routing.

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I'm just two people short of a threesome.

Reading your post and guessing at your skill level I would recommend finding a good shop. In an amp that old you could have a lot of different things causing your symptoms. The opamp mentioned is just a dual 741 and common as dirt, but you don't want to **** up the circuit board and shotgun parts. It needs to be troubleshot by a competent tech. Could be a tube socket or a bad cap. Could be bad connections or bad solder. If you are not used to working on tube amps take it to a pro.

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Stage Guitars: '80s Thin line LP Custom, '70 LP Standard, '83 Squier Black Headstock Strat w/ Dan Torres pickups, '59 Black Danelectro DC, sometimes others.

Pedal Board: Nady UHF 10 -> TU2 -> Rocktron Big Crush -> 70s MXR Phase 100 -> Cry Baby -> Bad Monkey -> Early '80s Rat -> Early '80s Ibanez CS 9 -> Ibanez DE 7 -> Behringer Dr 100 Stereo Reverb

Stage amps: '63 Blonde Tremolux w/ two original 2X10 cabinets with a '60 Ampeg Rocket/18 watt VTB Marshall clone/ Epi VJ into a Mashall 1965A

I'm not near my gear right now, but I'm pretty sure I had the loop gain switch set to -10 dB already. Last time I used the amp on its own it did the same thing. Last night I played the rig without once using the amp's preamp section. When the G9's FX loop module is off, it doesn't send or receive to or from the amp, so it's like having something plugged directly into the power amp. However, when I was playing it, at one point the amp suddenly cracked, then after a second cut to half volume. After about ten seconds it returned to normal. So I'm still not sure.

As for the reverb op amp, I'll leave that to a tech. If it's something on the mainboard itself, I'm not going to touch it. Too paranoid I'll gum it all up.

Now, I'm not experienced working on tube amps, but I do know of a great technician at a local guitar shop that I'm sure would be able to look at it. He's built his own unique amps, so I'm confident he knows what he's doing.

The reason I use the preamp with the master wide open is that I want the amp's sound on some patches, and others I want to contour the sound before modeling. Anything below 12 (maximum) on the Master pot just isn't loud enough on the processor. If what you're saying is true, I should be able to connect using the +4dB setting and use a lower master output for the same volume. My concern is that if I'm still driving the amp too hard, setting to +4 on the send/return will only further drive the amp at input. I'll have to experiment with it when I get some time.

I did go back and look at the power tubes while the amp was running yesterday. I noticed that one of the EL84s' heater filament seemed to be dimmer than all the rest. They all had the same faint blue glow, so they were working fine, but it's the fact that that one tube didn't seem to be in full operating condition that has me thinking I should retube. They are Sovteks in the power section, after all.

Just swap the power tubes in different sockets. If the same tube glow dim in another socket then it is the tube. I say to do this because tube filaments rarely fail in this manner. They either work or they are open circuit. The more likely cause of a single dim filament is a bad connection or contact to the the tube socket. Sometimes just uninstalling and remounting the tube a few times will reestablish the contact. But usually the socket needs to be resoldered, retensioned, or replaced.

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Stage Guitars: '80s Thin line LP Custom, '70 LP Standard, '83 Squier Black Headstock Strat w/ Dan Torres pickups, '59 Black Danelectro DC, sometimes others.

Pedal Board: Nady UHF 10 -> TU2 -> Rocktron Big Crush -> 70s MXR Phase 100 -> Cry Baby -> Bad Monkey -> Early '80s Rat -> Early '80s Ibanez CS 9 -> Ibanez DE 7 -> Behringer Dr 100 Stereo Reverb

Stage amps: '63 Blonde Tremolux w/ two original 2X10 cabinets with a '60 Ampeg Rocket/18 watt VTB Marshall clone/ Epi VJ into a Mashall 1965A

Okay. I'll still have a tech do it, the last thing I want to do is break something. Thanks for the tip, I'll be sure to run it by to check that.

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The Hindsight Rig

Some recordings and other stuff.

Lesson on acoustics in amplifiers.