Re: 4-1000A Screen Biasing...

[Parpp807-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Dan,
I would also urge you not to use a voltage divider resistor contraption to 
achieve 
screen grid voltage on a moderate to high power transmitting tube. It's not 
"elegant." The large wire-wound resistance becomes a nest of parasitic 
oscillations. According to the charts, you can put 5000V on the plate of a 
4-1000A. The screen
voltage would be 1000V at 0.075 Amps. If I remember the arithmetic for that, 
this means
a 33.33k Ohm resistor at an ugly 75 Watts. Perhaps I'm biased :-)), but I 
would use tubes
like a pair of 5R4GYs or even 5U4Gs in a well filtered supply that could be 
used with other
screen grid tubes. Don't forget a 10% bleeder across the output. Bypass the 
plate and SG leads with a capacitor having a low Xc at the TCs f res. Also, 
there is always a
handful of HV diodes. ;-)) 

I have 833s, 838s and 811s. All triodes. IMHO, I would not mess with tetrodes 
or 
pentodes for all the nuisance. IMHO.

Happy day,
Ralph Zekelman