|[AMRadio] Modern Equivalent of 35T and 203A|
crawfish at surfmore.net
Fri Feb 4 20:36:52 EST 2005
Thanks, Don. I have one 838. Was going to look it up and see what it was
for. That circuit just looks like a winner. Of course, with my newly
acquired supply of 4-125's, I will go that route. Still looking for mod
transformer.Again, thanks to all who responded!!
Donald Chester writes:
> You might be able to use a pair of 838's or 805's in place of the 203A's.
> The 838's have the same pin connections, while the 805's bring the plate
> lead out of a plate cap on top of the tube; otherwise they are essentially
> the same tube, with the same filament current as the 203A. The 838 and
> 805 run zero bias up to about 1000 volts on the plate. Above that, they
> require a few volts of bias to keep the resting plate current at a
> reasonable value.
> Also, a 211 is a near-identical tube, but it is lower mu, and would
> require larger grid voltage swing and more bias, so your present audio
> driver might not work satisfactorily with this tube.
> I have seen 203A's advertised from time to time, not any more overpriced
> than other triode transmitting tubes in this era of audiophools with an
> excessive supply of oxygen-free money but lacking in fully oxygenated
> Don K4KYV
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