[AMRadio] Modern Equivalent of 35T and 203A


Joe Crawford 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!!
                                          Joe W4AAB 


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 
> brains. 
> 
> Don K4KYV 
> 
> 
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