Interesting idea. Nominal screen current is 35 mA and voltage is 325. Current goes
negative in zero-signal state so the regulator has to deal with that. I want to be able to
vary screen voltage for experimentation. Lower voltage gives better IMD if someone wants
to operate SSB, higher will give more output on CW.
On 9/1/2012 7:11 PM, Bill, W6WRT wrote:
ORIGINAL MESSAGE:
On Sat, 1 Sep 2012 17:55:48 -0700, Jim wrote:
Why not just lift the negative end of the HV bleeder with zenner diodes? If
the plate voltage goes away, so does the screen voltage. I hear that screens
don't make very good plates?
73
Jim W7RY
REPLY:
That will work, but it requires some very high power bleeder resistors. For
example, if the HV is 3 kV and your screen requirement is 400 V at 80 mA, the
total power dissipated is 208 watts in the resistors plus the 32 watts for the
zener. It's just that much more load on the plate transformer.
It's certainly an alternative but that's a lot of HV to throw away. As for
protecting the screen when HV is lost, I'd include a simple HV detector that
shuts down the screen supply when HV is lost.
73, Bill W6WRT
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Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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