[Amps] Dual GS35b input impedance

[jeff millar]

I've seen a variety of values for GS-35 input impedance over the range 
25 to 100 Ohms.  It varies between tubes because the grid bias varies 
with these russian tubes.  I tend to believe the input impedance runs 
towards the low end of that range.  It runs lower than 8877 and the like 
due to the high grid current.  Cathode drive impedance is proportional 
to Eg / (Ip + Ig).

Definitely halve the impedance for two tubes in parallel.  It might well 
end up 12-25 Ohms.  Running high plate voltage will increase bias and 
increase input impedance.

jeff, wa1hco

Tomm Aldridge wrote:

> I am now at the stage of designing my tuned input for the dual GS35b 
> amp that is in process here.  There seems to be a general concensus 
> that the tube presents a 50 Ohm impedance when cathode driven in GG 
> configuration.  Can I assume a 25 Ohm input impedance as a good 
> starting point for my input filter design?
>
> Regards
>
> KD7QAE
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>