Tube Amp Archive

Very little noise at this point, if any. Settled on a 1.2k grid resistor. I also changed to the 2.2m resistor on the input grid to ground as recommended. I’m going to run the amp through its paces tomorrow after reinstalling in the head enclosure. Thank you for the suggestions and patience. I really...

It seems the straight wire to the grid and the 2.2m resistor have the most dramatic sound effect. I also noticed that having the jack floating away from the chassis has also reduced the noise. It is such a short distance, maybe one inch, from the tube socket to the jack that I didn't use coax cable....

I'm trying to understand what the shunt is doing here. I've been reading online that shorting the grid to cathode ground would bypass or short out that section of the tube. If that's the case, then when I shunt the input of the preamp tube and the noise disappears, it would mean that the problem lie...

Rechecked and reflowed all of the connections. Moved the ground to chassis connection near the first filter cap negative and isolated the input jack from the chassis. Still noisy. Just wanted to do all of this before I continued the troubleshooting. I was able to shunt the preamp tube grid and it's ...

I did try the metal cap/cover to chassis ground a while back with no luck. Thanks for that tip. I also checked the those 5.6k cathode resistors and they were solid to the first filter cap negative, lowest ohms, 0. I didn't check the B+ to ground end of the cathode resistors or shunt the grids to the...

Well my cheap little scope/generator off of the web arrived...it's really cheap but worth a shot. If it doesn't work for testing the amp, oh well. I'm just wanting to find out if I need to make some kind of 'dummy load for the speaker output' for my particular noise issue. I'd need to go get some hi...

I decided to order a oscilloscope and it will arrive today so once I get it and figure it out, I'll have a go at scoping the amp.

As this is my first rodeo using a scope, what would be a good order of troubleshooting/pinpointing this noise?

Thanks.

So is that capacitor to ground probe I was using earlier acting as some sort of voltage divider to ground, reducing the plate voltage or eliminating it altogether? I didn't have a free hand to check the plate voltage at the preamp tube and I didn't want to fix the probe to the plate pin as to not da...

Attached the first cap negative to chassis right near the OTG and no change in noise. Still present. Here's the results from using the probe and connecting one side to ground and the other to the first 6 pins of V1. Grid #2 (pin1) - noise lowers Plate #2 (pin2) - noise disappears Cathode #2 (pin3) n...

Dangling in the air shows no connection to chassis. Mega hum when powered up. More of a constant hum than buzz like is the noise I'm dealing with.

With power off to the unit and the jack dangling in the air, there is continuity to the OTB and no continuity to chassis.

No dimmers here but yeah that's what it sounds like. I've got an area in my garage studio that has power lines overhead and I can't use certain mics without situating them at certain angles to cancel the noise. It's a pain. On the other end of the house, dead quiet. That's where I took the amp and t...

I don't have any new PS filter caps but I have some NOS multi-can caps that I could try out and see if that solves the buzzing sound. I wish I had a scope I just don't do this enough to warrant the need for one. I did try replacing the 5u4 rectifier tube but still have the buzz. Seems like this is p...

I tried a different spot in my house, but still have the buzzing coming through the speaker.

I will say that the bass amp sounds coming from the amp sound great...just the buzzing that will probably be an issue when recording.

I've got a three wire (hot/neutral/ground) power cord connected. I have the green/ground wire bolted to the chassis where in comes in which is another modification to the schematic I made. No fluorescent fixtures around, just led lighting. I will take the amp to another location in the building to s...

I decided to shorten things up inside and moved the tubes around in the fashion of the original layout of a b15n. Attaches are some new photos. I still have the same noise present. I've followed the grounding scheme as the first cap as the OTG. The PT CT is attached here as well as the output tube c...