>> From: Rich Measures <measures@vc.net>
>>
>> For adding a step-start relay and high speed switching, a FWB is
>> indicated. Half-wave rectification causes DC to unhappily flow in the
>> transformer. Adding 3 more diodes and ungrounding the 80v winding is
>> easy/inexpensive.
>
>The very small power demand of the bias supply (about 12 watts)
>would not greatly affect the core losses of a transformer already
>delivering 160 watts to a resistive load.
>The half wave rectifier is perfectly fine.
- 20uF in half-wave service is perfectly fine for filtering the original
20mA load, however, it is a bit lacking for filtering the 100mA that the
high speed switching and step-start circuits consume. Increasing C is
one fix. Doubling the ripple frequency, by converting to FWB
rectification is another fix. 3 rectifiers cost less than another filter
C.
>If I was going to do a mod, I'd get rid of the whole 130 volt supply,
>and let the tube self-bias off. Than a more conventional 12 volt
>relay could be used.
>
Self cut-off biasing is good. However, conventional relays are too slow
to keep pace with modern radios.
Rich---
R. L. Measures, 805-386-3734, AG6K
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