I'm thinking about this issue now for my project 4CX1000A amplifier. The problem I see is
the first element getting chopped by the screen relay pull-in time, which would have to be
under 8 ms. to work. I am going to use a fast bias switching arrangement along with the
QSK RF relays as usual, but it would be nice to also switch the screen voltage.
Presently, I'm planning to have an "amp enable" switch which will turn on the screen
voltage and connect the transceiver key out to the QSK relays. So the amp won't
necessarily be 'armed' whenever it is warmed up and ready.
I have an extra vacuum relay that I could use for this, but Ian's board seems to be
designed for a 12v relay in this spot!
On 10/30/2012 1:20 AM, Ian White GM3SEK wrote:
The problem is how to switch these relatively high screen voltages RELIABLY at full QSK
rates. MOSFET switches have been tried, but are destroyed by the first HV arc that comes
along... so that means mechanical relays, which have their own different set of problems
including a limited mechanical lifetime. The best scheme I've been able to come up with
is to use electronic grid-block keying for QSK while *also* switching the screen relay
with a short hang-time to avoid it switching on individual dots and dashes. This gives
the advantages of both switching methods but requires some careful sequencing.
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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