>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.
>
0.8v change with a 4mA change in load current indicates that the dynamic
Z is c. 200-ohms?.
>Have you characterised the two-tone IMD performance of your 4CX250R
>amplifier at different power levels?
I test IMD with speech by measuring the relative signal level in the
windows. 3.6kHz above and below the fundamental. .
- later, John
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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