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In case anyone is following this... Someone from another website suggested replacing the RCA cable. Apparently, they had had a situation where a cheap unshielded cable caused reverb feedback. So, I removed the tank and connected it with a new RCA cable. It worked! With the reverb tank sitting...

I wonder if my problem might be similar to this... Cold solder joints causing amp to "feedback" whether a guitar is plugged in or not. Hmmm...

I found a website that tells you how to drain capacitors without using your tongue. ;) How to drain the filter caps What I'd like to see is detailed instructions on safely removing the chassis on a Fender Twin. Ever done that?

C'mon people! Doesn't anyone have any helpful suggestions?

Pay someone that knows what they're doing to fix it, eh? That's quite a concept you got there! ;) Nawt yet... Methinks I'll try to verify that all the existing components are within specs before I throw in the towel. :D I checked the tubes. ! checked the tank. What's next? Maybe pull the...

Okay, I tried swapping out all of the preamp tubes, one at a time. No joy... I'm about 99.999% positive that it's not a microphonic preamp tube causing the feedback. So, I pulled out the reverb tank... ...but I didn't see any obvious problem with the tank, like a loose wire, broken...

Dude, I'm afraid to even look at a capacitor! :eek: If it comes down to modifying the circuitry the way you describe, then I'll take it to someone like you that knows what an ohm is.

Yes, I swapped it with the original tube that came with the amp--a Groove Tube 12AT7. It didn't fix the problem. In fact, it might have made it worse. The cable from the reverb tank looks like a normal RCA cable. It has two wires and the connectors on the ends are color-coded (red & white)...

This amp does have a tube-driven reverb. I think the 12AT7 tube in the V7 position is for the reverb. The tank is mounted as you described, in a vinyl bag attached to the bottom of the cabinet with screws. I can't tell if there are any rubber isolating washers. I haven't done anything with it...

Why does the amp only feedback when the reverb is turned up? If it's a microphonic preamp tube causing the feedback, then shouldn't it feedback even when the reverb is turned off? Why does the reverb setting have any effect on the feedback? If there's no feedback when the reverb is turned...

I have two extra 12AX7's. I ordered two Ruby 12AX7A's from Guitar Center before I decided to replace all of the tubes with JJ's (Note: The Ruby tubes I got from GC are just JJ tubes with a Ruby label added). I don't have an extra new 12AT7, but I do have the original Groove Tube 12AT7 that came...

Okay, I'll try that... But what if the problem is actually a combination of two or three bad tubes? This amp has a total of 12 tubes (seven 12AX7's, one 12AT7, and four 6L6GC's) and any of them might be microphonic, right? I could be swapping tubes in different combinations until hell freezes...

Well, I removed all of the metal shields (vibration dampers?) from the preamp tubes and let the amp warm up. Then I tapped each tube several times, including the power tubes. All I heard was a tiny bit of noise that sounded like small vibrations coming from the springs in the reverb tank. And...

Thanks for the replies guys! Extra thanks to oldguy for checkin' out my pics. I'm glad you like 'em. So, I just tap on the tubes and listen for strange sounds, eh? I guess that sounds easy enough. Even for me. In fact, I'll go give that a try right now.

Hi People, I just discovered this place and this is my first post. I'm hoping you folks can :confused: help me diagnose a feedback problem that I'm having with my Fender ProTube Twin-Amp. I just bought this amp off eBay. It's a used amp, but it looks almost brand new. According to the folks at...