Isolation transformer installed....hum

[nickb]

Oh uh!

If it's all wired up as instructed the ripple current would be a little over 100mA. The cap was rated for 5000 hrs @ 105C and 430mA. It should have lasted way over 5000 hours. So, I suspect things are not wired up quite right.

[pontiacpete]

Here's drawing of my wiring.

[nickb]

That is wrong. What is more the cap in series and back to front. As shown it would not work at all* so it's not wired up the way you think it is. Take a look at this
Kent Model 5999 with Safety Mods C.pdf

*PS: I just remembered that a polarised electrolytic behaves like a really bad diode. That would explain why it's working and getting hot. But the heaters will be low voltage and the hum will be bad.

[pontiacpete]

Ah ha,,,,
Now I have it the right way. The only thing getting hot is the resistor now. I'm sure this one can take it.
I'm going to mount it to the outside of the chassis.
Thanks so much Nick! The hum is way less now.

If you don't mind just one more question, I've installed quite a few of these isolation transformers to make an amp safe but never had this much of a problem with hum. What is it about this amp? Is the pentode in the pre amp the main problem here?

[nickb]

I wouldn't blame the pentode. Probably layout mainly and expect it was hummy to begin with.