>
>
>
>> Rich said:
>>
>> >// Why not use a simple zener-string shunt regulator and obviate the
>> >needless complexity?
>>
>> Because they don't regulate well enough. John, GW4FRX, did a lot of work on
>> this some years back, and showed that zener regulation of the screen
produced
>> far more splatter than electronic regulation.
>>
// The quality of regulation depends on using quality zeners and
understanding the Looneytunes dissipation ratings -- i.e., don't exceed
more than c. 35% of the diss. rating and put the zeners in the path of
airflow to the 4cx250 sockets.
>> It may well be good for HF, but not for VHF.
>>
// I built a 2x 4cx250R 2m linear-amplifier that delivered 900w PEP.
When loaded for c. 5mA of screen-current it was as clean as the Kenwood
TS-700 10w SSB transceiver that drove it. The screen was operated from a
400V zener string that was biased from a 100k? resistor connected to the
+1200V tap in the +2400v FWD anode supply. Screen V-regulation was quite
good. Current in the 100k R was c. 8mA. Thus c. 10w was consumed by the
screen supply zeners and 100k dropping R.
cheers, Peter
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|