Re: GZ34 - recommended brands?
One of the great advancements I think with indirectly heated rectifier valves was the 6X5.
Relatively low forward drop around 20v for a 70mA plate current, could run the heater off the same 6.3v supply as other valves in the radio, didn't need the 5V winding on the power transformer. All in all a leap forward in efficiency for valve radios. These came out either in the late 1930's or early '40's, quite revolutionary.
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