Re: 4-1000A Screen Biasing...

["Steve" <Steve-at-g8cyerichmond.freeserve.co.uk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In amateur use, bias is usually provided by a separate supply. Commonly in
high power tube linear amplifiers the grid is actually grounded, bias is
then applied between the grounded grid and the cathode. This does increase
the complexity rather, but it is a lot more efficient (no heat producing
power resistors). Various methods of controlling grid bias are used. I have
only done this at VHF & UHF -at- the 500W level, and it was a long time ago. If
you have another look at the ARRL handbook you should be able to see actual
circuits.
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, July 27, 2000 12:22 AM
Subject: 4-1000A Screen Biasing...


> Original poster: "Daniel Boughton" <daniel_boughton-at-yahoo-dot-com>
>
> All:
>
> I have two 4-1000A tetrodes which I am using for a
> VTC. Does anyone have experience biasing the screen
> relative to the plate? The 2000 ARRL handbook lists
> typical screen current to be 146 mA for class CT
> operation and 145 mA for class CP operation(not much
> difference) with a screen voltage of 500V and plate at
> 3KV. Does this imply that that the screen bias
> resistor will have to drop 2.5KV WRT GND and limit the
> current to 145mA? This would require a 362.5 Watt
> minimum resistor! This obviously doesn't make
> practical sense so something is wrong. What is the
> appropriate means to bias the screen?
>
> Thanks,
>
> Dan
>
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