Noisy input on Michaelson & Austin TVA-1

[pix4work]

Hello,

Anyone ran into this before? On the input board schematic there are .022 and 5 pF capacitors, which seem to be the likely suspects for causing a small buzzing noise being fed to the output stage. Any ideas on what other caps it might be? I know I could just replace all the caps, diodes and pots, but has anyone worked on this amp before? A service manual would be greatly useful.
Has anyone seen one available? TIA...

pix4work

 

[SY]

Here's a schematic:

Schematic - Michaelson & Austin TVA-1 Tube Amplifier @ AmpsLab.com

The caps you mention would be unlikely suspects. What sort of buzz is it? 100/120 Hz sawtooth? Both channels?

 

[pix4work]

http://www.diyaudio.com/forums/tubes-valves/167103-noisy-input-michaelson-austin-tva-

It's higher than 120 Hz., maybe up around 400 Hz. and it's in both channels.

 

[apecg]

Hi,
Please check the grounding which is highly possibly the cause of the hum.

 

[DF96]

Yes, if its on both channels then either grounding or something in the PSU.

Blindly changing caps etc. is a good way to introduce new faults. If your doctor tried to cure you by just working though all the common medicines at his disposal you might be concerned; diagnosis ought to precede treatment!