[HomeBrew] 833 grouned grid?

[N2EY@aol.com]

In a message dated 1/22/02 7:12:01 PM Eastern Standard Time, 
w4chq@inetgenesis.com writes:

> Hello all,
>  Has anyone on the list built or used the 833 tube in
>  a grounded grid amp? I cant find any information on
>  the data sheets or circuits in old issies of CQ, QST and
>  73. I need some advise from someone who has experience using this type of
>  triode in GG service. I have
>  plenty of tubes and a 30 amp filiament transformer. My idea was to use two
>  tubes in grounded grid to simplify the construction.  But, I am worried 
that
>  the tube will not be happy without the -70 volts bias specified in the data
>  sheets? I dont want to destroy the tubes on first power
>  up. Will GG operation be possible with the 833?

GG operation is impractical with the 833A for reasons given by others. But 
don't give up!

My 1979 ARRL Handbook has a design for an amplifier using a single 833A in 
grounded cathode. The design is pretty simple - the input circuit is just a 
50 ohm noninductive resistor (50 watts) from grid to ground, and the bias 
network is just a pair of power Zener diodes (37V 50W in series with 23V 50 
W). The output circuit
is the usual pi network and the plate RFC is homemade. Neutralization is 
unnecessary because the grid circuit is so heavily swamped.

This amp will easily take a kW input at plate voltages from 2500 to 3500. 
Pi-net component values are given for 2500, 3000 and 3500 volts. Other tubes 
like the 4-400 and 304TH can be used in the design with slight modification. 
Operation is class AB2 and efficiency of 55 to 65 percent is reported. 

The design shown only covers 160, 80 and 40 because of the high capacitances 
of the 833A. Two tubes in parallel? Wow!

I don't know if this design ever appeared in QST (I think it did), nor how 
well it works, but it might be worth checking out if you have the tubes and 
associated goodies. It's no more complex than a GG amp of the same rating, 
and if you don't like it most of the parts can be reused.

73 de Jim, N2EY