Quote:
Originally Posted by Herald1360
The UCH21 is deliberately designed with separate grid connections for the triode and heptode sections (it uses the centre metal spigot to provide the extra, 9th, connection needed) so that it can be used in just this way. There's no UBF21 nor UCL21 to do the 4-valve trick in a more conventional way. Presumably the fairly high slope UBL21 was also used in conventional short superhets.
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Thanks for that Herald
Interesting to learn that the valve was
designed to work like that. I had just assumed wartime component shortage and a surplus of frequency changers to use up.
Embarassingly, when the set came to me with a request to fix it, i assumed (with some insistance- " it could never have worked like that!!") someone had been there before me and had been swapping valves.
The radio was a manky set with no dial glass serving a garage. I dont remember any power supply mods re 220/240V and it had daily use.
(Afterthought - maybe the uk model had a differnt dropper?)
(I dont remember the voltage selector markings but i probably wouldnt have paid attention......)