Re: Suspect Mains Transformer in 1930s Radio P.S.U.
Need for a bit of caution here - I've just seen your listing of the "proper" valves for this set, which agrees with that on the Radio Museum Website. If your ML4 is fitted in the L4 position (i.e. audio output valve) then, if it ever worked, the valve socket must have been rewired. An ML4 is an indirectly heated triode with pin 5 (centre pin) as cathode. Whereas the "proper" valve, PM24M, is a directly heated pentode using pin 5 as Grid 2, which would be connected possibly via a resistor to HT. The point is these 2 valves are not plug and play equivalents so I strongly recommend you check the wiring before purchasing another ML4. Assuming that you sort out the top cap the SP4 should work OK in place of the S4VB. I'm losing the plot with the other valves you have fitted (1821 is obviously fine) but I'll have a look to see if I have got any spares that will work for you against the "proper" list. Cheers, Jerry
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