Amps
[Top] [All Lists]

[AMPS] Screen Supplys

To: <amps@contesting.com>
Subject: [AMPS] Screen Supplys
From: measures@vc.net (Rich Measures)
Date: Wed, 19 Nov 97 06:44:02 -0800
>> 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   


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm

<Prev in Thread] Current Thread [Next in Thread>