[AMRadio] Modern Equivalent of 35T and 203A

Donald Chester k4kyv at hotmail.com
Fri Feb 4 19:56:25 EST 2005

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 


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