Tube Amp Archive

I removed the NF switch for now and put a switchable cathode cap mod in its place, moved the bias resistor so it's not crowded. Amp is quiet and stable throughout the pot ranges. I might just live with that. Thanks Gents.

pics

all sensitive wires are shielded at one end. coupling cap could probably be closer. I did notice while chopsticking, my NFB switch wires make hum louder when touched, do these need to be moved or shielded as well?

Ok, I forgot to mention that it only does this when negative feedback is removed and when either knob is maxed.

sounds like AC, doesn't oscillate. just a sudden hum. I switched to a 12at7 and this does not happen.

I've got a tweed princeton build here and it functions well and with quiet floor noise. Then when volume or tone pot is from 9 to 10, it suddenly gives off a hum. Ideas?

I meant I changed out the caps and added the 100k to v1b pin 7 and all is quiet. I also changed the cathode bypass cap from 25uf to .69uf.

All new caps

I moved the amp to my practice room and it almost sounds normal. I think I have some bad juju with my shop power situation. Further testing after the holiday. Have a happy one.

I did notice on older schematics there is a 100k resistor before the vol pot. I put one in and helped a lot, but now I get low oscillation on tone pot when turned down

Jumping from vol out to cap just before pin 5 yields quieter sound. Pots are scratchy though. These are all new components

Definitely not that, my dog let me know

Hi, I've just built a 5f2 amp, sounds good but at when diming either the vol or tone, it gets quiet and fuzzy. It's not gradual, it's a sudden change. Ideas?

In the usual high voltage B+ situation, 100k/820 is the norm. Now say I was running a 24v plate voltage, would these still apply? Or would one go for a much lower resistance pair? I'm attempting to marry a tweed type preamp with a parallel 12k5 power section at 12-24v B+. Thanks

Low voltage component availability. Have 12k5s laying around. Quiet practice amp