>> For small tetrodes with less than roughly 800v screens, a zener-string
>>
>> shunt regulator works best. For larger tetrodes, a 723-based positive
>> floating series pass regulator has advantages. You can find both types
>> at:
>> http://www.vcnet.com/measures
>> Rich---
>>
>> R. L. Measures, 805-386-3734, AG6K
>
>There is some data on G3SEK's web page, by GW4FRX, on the IMD
>performance of 4CX350s (which need about 400 V) using:1) A well
>stabilised screen supply.
>2) The screen stabilised supply with a resistor 150 Ohm added to worsten
>regulation.
>3) A zener diode chain.
>
>The results are the zener chain gives the worst IMD performance, ...
Not likely unless the zeners are improperly-biased and/or are defective.
>stabilised supply the best, and the stabilised+resistor in the middle.
>It not my data, but does rather indicate that zeners are *not* the best
>for small tetrodes.
>
Small tetrodes have the somewhat unpleasant habit of generating
potentially-fatal reverse screen current. A shunt regulator is ideal for
dealing with this unpleasantry. In the 1950's, Eimac recommended using
a shunt regulator made from a string of OA2 and OB2 gas regulator tubes
for its smaller tetrodes. However, a series pass regulator with a
sufficient bleeder resistor will do essentially the same job.
- If the zener-string/chain is powered from the anode supply through an
appropriate resistance, the screen is automatically protected against
loss of anode potential -- and there is no chance of damaging the screen
by too light loading or by sudden loss of the antenna during a tornado.
... ..
Rich---
R. L. Measures, 805-386-3734, AG6K
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