I'm afraid the speed up circuit you
mention does not work very well for the
vacuum relays. It indeed does speed
things up but the circuit doesn't
release the relay fast enough for true
QSK. The test setup I used is as
follows; your circuit with a TIP-142 +
50uf charge cap and an IRF-620 to pull
it low. The IRF-620 has the gate loaded
with 10k and is keyed with a TTL signal
@10-20hz. The relay is a Kilovac HC-!
with coil voltage of 26.5.
Here's the bench mark for the relay
keyed with the IRF-620 only and no
clamping diode(.1uf 300v ceramic cap
Make time, 2.32ms, this includes 600us
Release time, 900us
Remake time of NC contacts,(9vdc applied
to contacts), 2.30ms
Your circuit with 50uf;
Make time, 1.16ms, same 600ns of bounce,
Release time, 39.5ms, (slow!!)(this was
the 10hz key rate)
I did not measure remake time for this
set up, no point
Your circuit with 10uf;
Make time, 1.44ms, same 600ns of bounce
Release time, 1.48ms
Remake time of NC contacts, (9vdc
applied to contacts),10ms
This slow release/remake time was
discussed in the description by K6XX.
The relay supply has to charge the cap
before it will release, bigger
cap=faster make=slower release.
I don't believe you're going to hear
very much between Morse characters with
these remake times.
This circuit could eliminate hot
switching for the clunky open frame
relays in older amps or in non-QSK
vacuum relay amps but high speed QSK is
not going to happen.
The same relay keyed with a 33vdc
un-regulated supply closes in 2.1ms and
remakes in 2.05ms, no extra parts!!
More than four dozen relays have been
measured here with the same results,
(ITT Jennings RJ1A was faster but died
after 750K operations). The published
make times of these relays are
GUARANTEED maximums and include
aerospace applications involving
multiple G's. Typical make times here on
earth are much less.
Bottom line, measure it's speed first,
it could be OK for your application
right out of the box!
QRO HOMEBREW COMPONENTS
> However, you don't actually
> *need* a high voltage supply
> to achieve this
> speedup. You can do almost
> the same from the existing
> relay voltage, by
> using the one-transistor
> circuit developed by K1KP.
> Using this circuit
> with the normal 24V rail,
> I've had 1.5ms closure times
> from a number of
> HC-1 relays... pretty much
> the same as Rich gets.
> Adding a 'universal' 12V
> low-current PTT interface to
> any transceiver,
> the circuit expands to a
> whole three transistors - see:
Click on the "April 2002" link for more
details of how it works.
It's an easy mod to almost any
amplifier, and will also speed up an
existing open-frame antenna relay.
Bringing the closure time down from
about 30ms to more like 15ms can
sometimes cure hot-switching problems
without needing to change the relay.
BTW, my favorite source for vacuum
Allen Bond is a straight guy, and very
easy to deal with.
73 from Ian G3SEK 'In Practice'
columnist for RadCom (RSGB)
VHF/UHF DX Book'
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