Sounds like you might want to go with some kind of electronic bias
control scheme, Larry. (G3SEK probably has a circuit for this
on his website). This would cut the tube bias off during
standby, thus keeping the tubes cooler without the need for a
mechanical relay. Of course, when you go 24 x 7 (and assuming
you are not driving the tubes too hard) your main limitation will
become filament life. I am not sure, but with "instant on" thoriated
tungsten filaments, you may be able to come up with a scheme for
reducing during filament voltage during a significant portion of the
55 second dead times. You would need to talk with somebody
who has some expertise with the physics of tube filaments to be
sure, but there is probably some optiminum standby voltage
for the filaments that keeps them hot enough that the constant
cycling wont stress them out, but cool enough that the lifetime
is extended. The warm-up would from standby temp to full
emission operating temp would have to be fast enough (e.g.
<=15 seconds) to make the standby period worthwhile. Then
it would just be a matter of coming up with a solid state switch
that would place a ballast resistor or idler winding in series with
the primary of the filament during standby periods.
Of course it might be simpler (and cheaper) to just go out and buy
an extra set of tubes (easy way to double the system lifetime).
BTW, what's the application - some kind of beacon I presume?
73 de Mike, W4EF......................................
----- Original Message -----
From: "Larry Kayser" <firstname.lastname@example.org>
Sent: Sunday, August 18, 2002 1:28 PM
Subject: [Amps] recommendations please
> A small issue here, I make 360 transmissions per day at this time, 5
> seconds long per minute. In the future I may go to 24x7 operation when I
> can process all the collected data...
> I am using an ancient SB 220 and have been running it locked ON for each 1
> hour session of 60 transmissions. It would be a simple program change to
> key it up each minute 1 second before and unkey it one second after each 5
> second transmission.
> My question - which is best for the tubes which are the expensive part of
> the operation. I can replace relays much easier than tubes hi. I can see
> some reasons to go either way, but there may be an important reason I have
> not thought of.
> PS, The application is in the scientific side of amateur radio and of no
> interest here.
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