AC30 Noise reduction?

[Voxbox]

Hi guys,

I'm trying to reduce hum and hiss in a 1963 AC30 with a factory added T&B circuit.
best tweak so far is to "balance" the heater supply through two 100R resistors to deck. That reduced hum by 6dB.

Are there any other things to tweak to get the output hum down from 150mV pk-pk, which is quite audible and is coming from the output stage? Is output stage hum due to output transformer winding balance? There are no defective output valves and it doesnt matter what valves I use, the hum is still there.

Any other things to do to reduce pre-amp circuit hiss apart from putting in Metal film resistors, which I really dont want to do.

BTW I've replaced all electrolytics and the anode caps which were leaky.

It's the hum that I'd most like to reduce though.

Help!

VB

[tubenit]

Any other things to do to reduce pre-amp circuit hiss

Shielded cable where appropriate.
Smoothing caps across plate resistors (or plate to cathode)
Treble bleed on a volume (47p to ground)
Different preamp tubes with less gain such as a 5751 instead of 12AX7
Change treble cap in tone stack  to higher value

While not specifically preamp related there are some speakers that have more
 subtle high end frequency such as Emminence Red, White and Blues (which might sound awful with an AC30?)

With respect, Tubenit

[Voxbox]

Thanks Tubenit,

Sounds like good advice sir!

Everything is screened that can be.

Smoothing caps on plate resistors? A smoother to my mind is a Power supply smoother - 16uF plus. Do you mean an HF bleed cap? What kind of values do you have in mind?

As its an AC30, so much of that "chime" comes from the speaker, I'd be loath to change them to roll off the top end.

Thanks, cheers, VB

[HotBluePlates]

In an original AC-30, I'd be thinking bigger filter caps, since 16uF could be quite small. The modern AC-30's have a very different power supply rail.