[BC] 4-400s Versus 833s

[RichardBJohnson at comcast.net]

Triodes needed about 30 percent driver modulation, especially
those single-ended circuits that used transformer neutralization
such as CCA, ITA, etc. Tetrodes needed a small amount of
screen modulation, i.e., self-modulation using either a resistor,
a reactor, or both.

A well-designed tetrode final amplifier stage would use a fixed
supply for screen with a series reactor. However there would
be a resistor across the reactor that's value had been
experimentally determined for the optimum amount of self
modulation.  

--
Cheers,
Richard B. Johnson
Read about my book
http://www.LymanSchool.org


 -------------- Original message ----------------------
From: Tom Dimeo <mwam at pa321.net>
> Is it correct that the driver for triodes had to be modulated 
> to maintain proper linearity?  Was this the case for the 
> 4-400s too?
> 
> ** W2XJ Wrote: **
> >I have always felt that way about 4-400s. An 833 equipped 
> >transmitter had tube life measured in years. A new 20V3 with 
> >4-400s went 6 to 9 months on a set of tubes. I have always 
> >felt that it was just false economy, especially when 
> >electricity was dirt cheap. I think the argument about 
> >fidelity is somewhat misleading.  The Iron in a plate mod 
> >transmitter is the primary thing that determines fidelity.
>