Rectifier tube Filament center tap? now have video

[yalesmith]

Hello was wondering if I could and it would reduce hum if I created a artificial center tap (2 100 ohm resistors to ground) for the rectifier tube filaments?

Thanks

[Phil_S]

How do you know the rectifier is contributing hum and if it is how do you know it's on the filaments and not the HT secondary?

[yalesmith]

I have exercised all possibilities and have had this amp build for six months and cant get rid of the hum. How would I determine if it is on the HT secondary?

Thanks

[Leo_Gnardo]

Hello was wondering if I could and it would reduce hum if I created a artificial center tap (2 100 ohm resistors to ground) for the rectifier tube filaments?

Thanks

If you have one of those odd little rectifiers that run filaments at or near ground potential then why not try it? Might take 5 minutes. You also might find hum minimized with non matched grounding resistors. In a couple amps recently I found a combination of 120R and 82R gave optimum results but those were amp tube filaments not rectifier.

If it's one of the usual run of rectifiers (5AR4/GZ34, 5U4, 5Y3) that run filament at B+ potential you will have a couple of very roasted 100 ohm resistors very fast. In which case you should skip this experiment.

[yalesmith]

yeah it is a gz34. That is what i thought thanks.

[Leo_Gnardo]

yeah it is a gz34. That is what i thought thanks.

OK then spare the resistors and let's look elsewhere for the source of the problem. I'm in Dutchess County. Send me a PM and maybe we can get together and sort out your amp without having to give ourselves typing cramps.

[pdf64]

Have you confirmed that the hum is definitely 60, rather than 120Hz?
If confirmed 60Hz and you suspect the rectifier, sub in a couple of Si diodes and a chunky (eg 15W) 82 ohm series resistor to see if the hum disappears.
Pete

[M Fowler]

If you have fixed bias check the grounding of the bias cap.

[yalesmith]

Leo I will definetly take you up on that offer..... Take a look at the video and let me know what you think


Again Thanks alot guys, I hate bugging people with this amp again but it has been
6 months and i cant figure it out.

http://www.youtube.com/watch?v=2A9Mibw65Y8

[VacuumVoodoo]

Hum changes in volume when you turn that pot. That's a ground loop symptom. Either in a gain stage before that pot or the pot is grounded at the wrong spot in your grounding scheme. That's all I can tell from a distance.

[yalesmith]

The gain pot is grounded at the second stage, The cathode of stage 1 (EF86) is grounded at the input jack as well.