[AMPS] Screen regulator circuit needed

[John Nelson]

Message text written by Rich Measures

>Was not the IMD degraded by the shunt zener regulator?<

The IMD performance with the Zener chain was consistently worse than the
IMD performance with the active regulator. But how is that relevant to your
assertion that the Zener chain was "obviously flaky"? Are you familiar with
the devices I used? Are they "flaky" in comparison with other Zeners, or
other types of regulator? Please suggest a part number for Zeners which
will give better IMD performance than the BZY93 family. 

>What was the measured fluctuation in screen potential from zero signal to
max. signal with the zener shunt regulator?<

Using new 4CX250Rs in a modified W1SL 144MHz amplifier with 2.2kV on the
plate, 350V on the screen, the drive level adjusted to give a single-tone
output of 250W into a 50ohm Termaline and the loading set to give optimum
700/1700Hz IMD performance on an HP 8590 analyser (corresponding to
indicated Ig2 of about +2mA per valve), the regulation with the Zener chain
was about 0.8V. 

Have you characterised the two-tone IMD performance of your 4CX250R
amplifier at different power levels? Some numbers would be interesting,
especially for higher-order products. 


John Nelson
GW4FRX  


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