Hi!
Quote:
Originally Posted by GMB
There are interactions between the features so it isn't trivially simple.
By way of example, you might have expected various holes to select the heater voltage, but actually you find cards with different hole combinations in the heater area for valves with the same heater voltage rating. The reason is that they actually allow for the effect of the current drawn loading the transformer.
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This is something else that my study of the manuals didn't pick up and I'm not sure the military version CT80 manual makes it clear either!
To take 6.3V valves as the most common example, you've got currents ranging from 90mA for the EY51 e.h.t. rectifier to over 2 or 3A for many of the smaller glass–base transmitting tetrodes, etc. – the only way to determine the characteristics of the heater transformer for certain is to connect a controllable variable a.c. load with a reliable current–monitor to it – I think I've seen a project for a continuously controllable one somewhere, but it's not a trivial design by any means!
No doubt Mullard's design engineers were provided with loading graphs for the heater–voltage transformer, but it's certainly info I don't recall ever bsing documented anywhere!
Chris Williams