Hi to the gang.
I have been reading the mail about doing QSK by switching the screen voltage
with interest. I have a home brew 1200 Watt GU43 based amp which has had a
hard life.before it got to me. It has several types of switching relays
mixed in and stabilizer tubes to control the screen supply and it looks as
if a lot of the bits came from an R140 setup(It was built by a Russian I
think). It has a 3kV anode supply @ ~ 1 amp
My question of Carl and the rest of the guru's is, that can reed relays be
used for the input and output switching if switching the screen supply fast
shuts the amp RF output down quickly.
I have a card of the Crydom frd 13501 RF rated reed relays with 6 amp 1A
contacts and 8500 volts peak voltage rating (these are normally used for QRO
auto tuners). I'm thinking of two in parallel to switch the output (one will
handle 1kW maybe but only if the SWR is good) and one or two in series to
switch the input. The spec on the relays is 3 mS on time (including bounce)
and 1 mS off.
The issue I think is that these relays will carry the current and do the
isolation but won't be able to do any hot switching so "killing" the output
before switching is critical. If I use one of the power mosfet screen
regulators available, and switch it quickly, how quickly will the RF shut
off ? In other words I can easily get the screen volts down low (say from
350 volts down to < 20 volts ) in under 100 uS, but will the RF be gone
before the 1 mS delay of the relay falling out has gone by. If this is
possible then a very fast simple QSK amp circuit is do-able.
Comments and flames please
Regards Bob ZS6BXI
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