On Mon, 7 Jul 97 22:30:17 -0700 Rich Measures <measures@vc.net> writes:
>>> 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.
True, but the original discussion was about the capacitor failing and
requiring replacement anyway. The cost of a 100-200MF 160V capacitor, if
someone wants to add a bunch of extra parts will not require a 2nd
mortgage. The 90V winding on the xfmr is rated 100ma CCS.
>
>>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.
QSK operators are a small minority; the original relay is fine for the
rest of us.
73...Carl KM1H
>Rich---
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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