[Amps] Small transformer evaluation

Vic K2VCO k2vco.vic at gmail.com
Sat Sep 1 23:39:35 EDT 2012


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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