For simplicity, I would suggest the use of the Clare PLA140 opto-isolated
"solid state relay".
It can hold off more than 300 VDC and has a current rating of 200 mA.
Switching times are in the 0,5 ms range with 10 mA input drive.
The even faster International Rectifier PVA3354N opto-FET switch can be used if
the
steady state current is limited to less than 120 mA.
Both have been used to interface tube-type PA's to solid-state control circuits.
73/
Karl-Arne
SM0AOM
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "JOS Earthlink" <jsternmd@earthlink.net>; <amps@contesting.com>
Sent: Saturday, December 09, 2006 12:12 PM
Subject: Re: [Amps] Optoisolator for Keying Collins 30L-1 to Modern Rigs
> > Question is for routine SSB (and some occasional CW) does
> > one really need an
> > optoisolator circuit controlling a relay rather than just
> > a lowvoltage power
> > source plus a well rated (250vdc 2a) low voltage relay?
>
> The problem with a relay keying another relay is activation
> times are added. Whatever small relay's time you add in, it
> makes an already poor situation worse.
> Say you have 13mS on the large amplifier relay and 5mS on
> the small relay. Pull in would now require 18mS.
>
> Virtually all rigs actually output RF before the antenna
> relays can transfer in an external PA. This can cause
> amplifier bandswitch or tank component arcing or damage,
> annoying pops or clicks up and down the band, and chopping
> of the first part of transmission at every VOX or key
> closure if you are not using push to talk or manual transmit
> switching.
>
> With a solid state buffer circuit you don't add the time of
> another relay.
>
> It does not take a special expensive circuit to do this or a
> high speed relay. All it takes is one or two transistors, a
> resistor or two, and a diode. You can also use a very fast
> external relay, like a HV reed relay, but you have to watch
> voltage and current transients.
>
> It might be less time and worry to buy one. Ameritron also
> offers a relay buffer. But they are easy to build.
>
> 73 Tom
>
>
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