Sunday, June 7, 2009

Peavey Classic 30 Reverb Howl

This is another one from the slightly odd repairs file. Here's the reverb pan from a Peavey Classic 30 which came to me with a complaint that the reverb was "humming and feeding back".

Peavey Classic 30 reverb pan

When the reverb knob was turned up past 3 the amp made a pulsing howl which got louder the further the reverb knob was turned up.

Suspecting some magnetic coupling I took the reverb pan out of the amp, leaving the wires connected. By orienting the tank in different ways the problem could be greatly reduced but I couldn't get it to go away completely.

Disconnecting the RCA plug from the input jack on the reverb tank itself didn't affect the howl at all. Reconnecting it and disconnecting the outplug plug stopped it completely.

The quickest next step would be to swap out the tank to see if it was bad. Below is the Accutronics reverb tank part number 4EB2C1B printed on the tank itself:

Peavey Classic 30 Accutronics Reverb Part Number

Fortunately I happened to have another on of these around the shop. I plugged in the substitute and the amp was back to normal with a perfectly working reverb.

Now here's the odd part (and the reason I'm bothering to post such a run of the mill repair). I always try recheck once a repair is finished to make sure what I've done has actually fixed the problem. So for good measure I plugged the original tank back in. Now the amp worked fine with the original tank! Even though I'd plugged and unplugged the orginal tank a number of times somehow the act of plugging in the replacement tank caused the original tank to make a good electrical connection. I've seen oxidized or poorly toleranced plugs cause reverbs to stop working or have intermittent signal, but causing this howling was a new one on me. It just goes to show, it always a good idea to clean jacks and plugs even if you don't have a reason to suspect them.


Ben Dobberstein said...

I did a search a few minutes ago for "repair reverb unit classic 30 tube amp" and your blog came up! It's funny, cause that is exactly what mine is doing. It continues until you turn the reverb knob all the way down. I don't have another unit available to test this out like you did, but I have disconnected both the input and output leads, reconnected, and the same problem continues. Nothing's obviously wrong. It's such a primitive technology, it should be a fairly obvious problem to solve, I'd think. Anyway, I'll keep you posted, and if you run across anything that might lend itself to a cause, let me know!



Anonymous said...

Hi guys. Have just acquired a relatively new classic 30 212. Have similar prob with a noisey reverb. The thread is a little cold, but if anyone picks it up can you please let me know suggestions. Will definately unplug and clean connections tonight and re-orientate away from transformer.

Anonymous said...

I had the identical problem with an older well-played Classic 30 I bought mostly untested, but the price was too good to pass on. I was dissappointed when I got it home and set up. The howl started at about 3, just as described, and continued until turned all the way down.

Having read this thread, I looked at the RCA connections to the tank and popped them on and off a couple of times. They did seem clean and tight. And no joy, the behaviour was the same. I hit the connections with contact cleaner and wiped them...quite a bit of grime came off. So I reconnected and fired up. Beauty! The amp performed perfectly with fully functioning reverb and no howling at all.

I am now very pleased with my new amp. So the lesson is take some care cleaning these connections and there is a good chance you will experience the same easy fix I did.

Thanks so much to everyone who took the time to post their insight!

McQ said...

Hi, I've just sorted the Reverb tank hum on a Peavey Classic 30. I've had a few problems with these over the years. (I used to have a Classic 50 - then a 2 x 10" De Ville which both had this problem. I removed the tank & put rubber draught proof strip (99p from any hardware store) around the base then taped a piece of cardboard to the bottom of the tank. Then wrapped the whole unit in bubble wrap. Cutting little holes for the connections then placed(screwed) back into the cabinet base & it worked no problem. This is a very easy cheap solution. You can buy tank covers from Ebay but the cheapest one I saw was £30. NB the cardboard taped to the bottom of the tank stops the bubble wrap from hitting the springs.