Tube Amp Archive

Pulling V2 the hum still remains. There is nothing before V2 in that channel of the amp ( the Top boost). Other tubes have already been tried, so early on that I may have forgot to mention it. Azatplayer, I'm going to have to believe that this is a common problem. I've seen numerous posts on the sub...

Well, the hum is centralized on the b portion (as per schematic) of V3. I have found that if you ground the grid (pin 7) the hum is increased or at least changed. Pulling V2 does nothing, hum is still present. I am looking for any thoughts on this, as I am running out of ideas. I did notice that Vox...

I don't know what I was thinking when I first posted this, but I just realized I said it was a 120hz. It's actually a 60hz hum. Sorry about that.

Thanks for the input Rich! I replaced the resistors at R36 and R35 and, alas, the hum is still there. I keep staring at the schematic, hoping that something is going to trigger an Ahah, but I it's just not happening

The noise is definitely in the cathode follower stage of V3. Grounding the grid coming from V2 changes the hum but it is still there. Grounding the grid in V4 from V3 takes it away altogether. I have already replaced C24 C23 and C15. Only C19 remains original as I didn't have that value(50pf@500). T...

The only way I seem to be rid of the hum is when I probe either of the grids on V4 for voltage. Tried pulling them (the leads) at the grids and hum got louder. Argh.

I'll recheck the grounds, but last I checked they were all good. There are no tube shields on the preamp tubes. And the the cap at C17 was replaced. The amp hums no matter where it's plugged in, including other locations. And no, I didn't lift that leg on the volume control. I've read similar thread...

I am working on a Vox AC15 handwired head that has a 60hz hum with volume all the way off. The owner says it didn't do it when it was first purchased. I have replaced filter caps, checked grounds and pretty much everything I could think of so far. It is less than a year old, has new JJ tubes in it a...

Well, I got the amp the other day and found that indeed the cathode cap was bad. Replaced it (mounted it on the board away from the resistor) and all voltages were back to normal range. But I'm still getting a lot of heat from that area and from the transformer. looks like they tried to jam too many...

Thanks for the input guys! I seem to have been on the right track at least. I explained the cap situation to my friend and he's decided to UPS the amp to me for repair after all. He said he doesn't want anything to do with capacitors!
So I'll let you know what transpires once I get it. Thanks again!

Well, I'm new to this forum but I thought I'd give it a shot. I'm trying to help a friend out with his Ampeg Reverberocket that started to run hot for him. Problem is, it's a long distance diag since he lives about 350 miles from me. He said it stared to run hot after doing a show out in the sun on ...