Thanks to Mike T (
Cobaltblue) and Lawrence (
ms660) for the heater chain information.
Quote:
Originally Posted by Ambientnoise
I think this has been mentioned but the UL41 is def prone to hum due to internal leakage. I see you have changed it but is the replacement new ? They can be zapped to fix this, do a search for “zapping a ul41” or similar, in the forum. A DAC90A of mine was bad until I replaced the UL41 with a new one. I guess the valve base could give the same problem so if the valve is def OK, a new base could be the next move.
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I've gone back and re-read everything I could find on UL41 internal leakage but can't find anything definitive on how to test for that? My idea (!) was to somehow test each valve out of circuit in turn, but in the absence of a valve tester?
I mentioned earlier that V4 had been replaced with a CV1977 and that I had rechecked all my valve voltages, including heaters, and there were no surprises.
Thanks to Tony (
boxdoctor) I understand that the
'...colour of the getter is often a good pointer to the state of the valve, and kind of life it has had. Usually valves with a good silver getter are more likely to be OK, assuming no O/C heaters or other mechanical faults.' My CV1977 has a nice shiny getter flash on the inside of the valve envelope.