Tube Amp Archive

The Supro amp hum has been solved!! WOOOO HOOOOOooo!!!

It now has a "normal" very faint hum that does not change when any knob is turned or volume maxed. Just played my G&L Legacy and all I hear now is the guitar!!

I'm so thrilled. Thanks to everyone who chimed in on isolating this.

Well, I ordered from Tube Depot: a matched set of EHX 6973's, a matched quad of JJ Gold Pin 12AX7's and a Mullard 12AT7 I went ahead and paid the extra few bucks to have them test for Low Noise & Microphonics, and Balanced Triodes. I don't know if they actually do that, or just have trained squirrel...

Thanks for the replies everyone. I think the safe route is to order a new matched pair of the EHX 6973's just to confirm the problem is solved. I can always buy NOS later. I'll probably order a matched quad of 12AX7's and a new 12AT7 to round it out. One of the tubes that came out of the back - wher...

I really don't want to have to use Electro Harmonix again. Is this a good deal? https://www.ebay.com/itm/Pair-of-RCA-6973-NOS-NIB-Vacuum-Tubes-2-Gm-matched/223392341011?hash=item3403389c13:g:lE8AAOSwndBcZfvv:sc:USPSFirstClass!84107!US!-1:rk:8:pf:0 The hat/top on that one looks crooked. Is that ok?

Pulled the power tubes and left the speaker connected.

It's dead silent.

I removed the rest of the preamp tubes, leaving just the 2 power tubes installed and speaker connected.

It still hums.

I got the chassis out. I removed the 12AX7 Phase Inverter and 12AX7 Preamp from around back and also disconnected the reverb RCA jacks from the chassis. With the speaker connected, both power tubes in, and I left the 12AT7 reverb driver, 12AX7 reverb gain and 12AX7 tremolo tubes in, it still hums. b...

Just found this last night. This drawing appears to show one of the preamp tubes on the back!! Weird. I'll pull the chassis tonight. What I found was that there were (2) two 12AX7's on the front made by EHX, which I ASSUMED were the preamp tubes. Therefore, when I got my matched set of 12AX7's from ...

xtian wrote: ↑Wed Feb 20, 2019 10:14 pm If there's still hum after pulling the PI, also pull the power tubes. Any hum left? If yes, it's PT electromechanical vibration.

Honestly, this has been my suspicion all along. I just didn't know how to isolate that to confirm.

Hi and thanks for jumping in. Your troubleshooting implies the issue is not in the preamp. So let's focus on what's left. Pull out the phase inverter tube (you know which one that is?) and evaluate the hum. If you still have hum, we know it's after the PI tube. That leaves mismatched power tubes, po...

Hello, I'm new here. The title says it all. I bought a reissue amp off of Reverb and it has a low-volume 60 cycle hum with nothing plugged in and all pots set to zero. Hum goes away in standyby mode. Hum is definitely coming through the speaker. Hum changes tone and slightly increases in volume when...