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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 25th Apr 2018, 10:48 am   #81
cathoderay57
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Default 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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Old 25th Apr 2018, 11:15 am   #82
'LIVEWIRE?'
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

Apologies for any confusion, Jerry. T.B.H. it's beginning to confuse me, but the first list - VU39(L5), SP4(L1) ML4(L3),, PM24M(L4), and MS4B (L2) are the valves which were in the 274A about 3 years ago, when I received it. They were in the positions I've indicated above, according to some notes I made at the time. According to an original printed label affixed inside the back cover, the valves should be (in the same order), 1821, MM4V, 994V, PM24M, and S4VB. As mentioned, I've already obtained & fitted a N.O.S. 1821, which is working well, at least, with no other load besides the new reservoir & smoothing caps and filter choke. If I'm correct in thinking that the ML4 (the smaller of the valves with the set) is the triode, that's the one which somehow got broken, whilst the SP4 (a gold colored Mullard one) has the later type of top cap. The MS4B may need replacing, whilst a substitute for the ML4 (994V) will be needed.
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Old 25th Apr 2018, 11:40 am   #83
cathoderay57
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Default Re: Suspect Mains Transformer in 1930s Radio P.S.U.

OK, thanks. As mentioned before, the SP4 is a reasonable equivalent for the S4VB but not for the MM4V, which is a variable Mu type (and the SP4 isn't). It might work, but is unlikely to perform very well. As mentioned in my other post I do have a spare VMS4B which is equiv to MM4V. I'll test it for you and let you know if it is any good. Cheers, Jerry
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