50 watt vs. 100 watt PS differences

[Heater]

Hey All,
I have a Hybrid A build with 4 6l6's for the output. The PS is built to the Hybrid A schematic. There is an existing 120hz noise in the amp that will not go away regardless of heaters, wire dressing, etc. I'm wondering if the filtering on the PS needs to be different to accomodate the extra 2 output tubes. Does anyone have any suggestions regarding the PS and possilble upgrade to the filter caps?

Thanks!
Chris

[Bob-I]

Other than more current, there's really no difference. I just completed a simple amp using a Twin output section, 4x6L6 and a 12AT7 PI and a single 12AX7 preamp tube. It's quite as a mouse and it's just using the same PS as the Hybrid.

Try disconnecting the heaters and connecting a 6V lantern battery. If the hum is gone, it's heaters.

[Heater]

Hi Bob,
Thanks for the reply. I did the lantern battery thing-no improvement. When I pull V1, the noise gets worse, when I pull V2 it gets a little worse again, when I pull V3, the noise is gone. It's definitely preamp related. I can trace it with a scope and find it in all 4 gain stages of the pre even if i disconnect previous gain stages. That's what makes me think that it's PS related. I've chased everything that I can think of. Maybe I'll just replace filter caps to be sure. I am able to measure some small amounts of AC from B1 downstream. How much AC is acceptable here?

Chris

[Funkalicousgroove]

I had a similar problem in an amp, it turned out to be a bad output tube (brand new) . the other thing it might be is your FET circuit if you have one. Check all your polarized caps and make sure they are properly oriented, and check all of your shorting jacks to make sure they are "shorting" also check your grounds.

[heisthl]

As a quick test put a cliplead to ground at where the 24K meets the 4.7K in the feedback loop. If that gets rid of it post back and I'll tell you where the noise is coming from - you won't like the answer.

[BobW]

I suspect the PI or B3/B2 Grounds. Verify B3/B2 is grounded at the same potential.

[drz400]

Tell us how you did your ground paths

[Darkbluemurder]

Does it get worse when you turn the volume and/or gain controls? If yes it is definitely preamp related. But your observation from pulling V1 and V2 indicates a PS or power amp related problem - otherwise it should have stopped.

Good luck!
Stephan