The only amp I've seen that used relays for tank coil switching was on the
fleamarket at Friedrichshafen one year. I think it was built by a Hungarian guy
and used Russian vacuum relays.
I can't particularly think of a reason why you couldn't make this work, though
someone may correct me.
On 10m in particular there can be a higher Q and thus consequently high
circulating currents, so you'd have to ensure enough current handling capacity
I can't remember what bands the Hungarian amp worked on, nor the chap's
callsign.
I do ask the question, however: if it's a piece of cake, how come no-one else
does this?
Good question, though - and one I've asked myself a few times!
Dave G0OIL
-----Original Message-----
From: "Rex Lint" <rex@lint.mv.com>
To: "Amps" <amps@contesting.com>
Sent: 13/03/2010 20:04
Subject: [Amps] Revamping a really ugly amp
I bought an old H/B amp that I'm totally revamping.
It's 2 x 3-500Z's with a 4KV power supply. It USED to have a pi-network
with a vacuum variable plate capacitor and a regular variable loading
capacitor, and the tank coil *was* a variable inductor so that the tank
could be adjusted for any transformation (within reason). I want to keep
the caps, but change the coil to discrete inductor(s) with taps.
I wonder if anyone uses relays instead of a rotary switch to select the
desired taps? What are the parameters I need to consider in trying this?
In my thinking, I'll just be switching the output side of the inductor, and
the impedance at this point (when tuned) should be about 50 ohms, so the
voltage isn't that high (350 V.?), and the current would be about 6 amps.
Relays for this should be a dime (well, $20) a dozen? As a mtter of fact, I
see one like this would handle the job if never switched "hot" which you
wouldn't want to do with a rotary switch either!
http://www.mv.com/ipusers/lint/K1HI/RelaySpecs.pdf
I'm also looking at compact tank coils in the literature. How much power
could I expect to run with two muffin fans to cool the tubess and operating
CW contests?
Thoughts?
-Rex-
Rex Lint, Consultant
26 Brek Drive
Merrimack, NH 03054
PH: 603-860-7651
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