Help troubleshoot hum in 100w build

[jelle]

Bias typically looks dirty. Does it look much dirtier than your other amps?

And, it is much easier to help you if you would post pics. Good luck! Jelle

[martin manning]

So how much AC ripple on the bias voltage? Did you try a different tube in the PI? If you had a HT arc to the filament circuit you could have blown the heater-cathode insulation in that tube.

[amplifiednation]

There is a little more ripple in the bias than in my other builds.

The short killed a 6L6 tube completely. I had to replace it. Any chance there could be damage to the socket? Or other damage I might not be able to see?

I'll try to post pics, but the amp is gooped

[JazzGuitarGimp]

I'm with Martin. Have you tried a new or known good PI tube?

[amplifiednation]

So I've isolated the hum to the preamp side of the amp, which is different than what i thought i saw with the scope. I might just start taking it apart until the hum stops. I don't know if that short would have caused more damage than on the surface...but maybe...

It hums with no tubes at all...so i don't think it is tube related. I didn't change the grounding scheme so it's hard to believe that's where the problem would be, but I will keep looking

[Structo]

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[Firestorm]

So I've isolated the hum to the preamp side of the amp ... It hums with no tubes at all...

Hums through the speaker with no tubes? What makes you think the problem is in the preamp?

[JazzGuitarGimp]

Have you checked all your DC voltages lately? It's possible something is pulling down the HT, which will increase ripple.

[martin manning]

What about damage to one or more of the filters, or a rectifier? With tubes in there should be only a few volts of ripple (p-p) on the first node, maybe half as much on the screen node, and almost none on the PI node.

[Reeltarded]

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Martin wears socks.

How come I either start or miss all the fun? Step it up, fellas.

[martin manning]

Martin wears socks.

But I've also been known to hum...

[amplifiednation]

Replaced the entire power supply board, amp still hums.

I'm starting to think the problem is in the OT

[martin manning]

You said it hums with no tubes installed; what about standby on vs. off?

[amplifiednation]

With the help of mhartman, we figured this one out.

I had tried to do more of a STAR ground, using cliff jacks.

We changed the amp to the standard Dumble ground and that did it

I changed to switchcrafts and moved the PI grounds to the return jack of the loop...then grounded the OT to the chassis instead of the jack.

Boom, no hum.

Thanks to everyone that helped.

[alvarezh]

Glad you sorted it out Taylor, very glad. Not an easy one by any means.

Thanks for posting this as it teaches us (me at least) what not to do.

On to another project!