25-05-2011, 04:57 PM
Either you have a VERY faulty UL41 or more likely there's no effective smoothing of the HT line. I'd cold-check the reservoir and smoothing cap (in the combined can). Failing any fault being found you'll need to work backwards from the output valve. Ground the slider of the volume control. If that stops the buzz it may be due to IF instability, in which case bridge C10 (Trader sheet number). It's the IF amp screen grid decoupler.Also try a similar cap from the HT line to chassis. You'll need a high working volts cap here for safety even though the line is unlikely to be above 200V.
Another slight possibility - the output valve grid may be floating and so picking up AC field.
I don't wish to teach egg-sucking and I apologise in advance for this, but remember this is a live chassis set. Keep one hand in your pocket, work on a live set with insulated tools such as sleeved screwdrivers and when bridging components, remove the mains plug, don't rely on the switch. I did apologise, didn't I?
-Tony
Another slight possibility - the output valve grid may be floating and so picking up AC field.
I don't wish to teach egg-sucking and I apologise in advance for this, but remember this is a live chassis set. Keep one hand in your pocket, work on a live set with insulated tools such as sleeved screwdrivers and when bridging components, remove the mains plug, don't rely on the switch. I did apologise, didn't I?
-Tony
