I saw one in Cedar Rapids that was built at Collins for what appeared to be
the upper end of HF spectrum. Lot of small silver plated tubing coil
sections, many ceramic caps and bunch of vacuum relays to switch everything
Looked like something military or commercial.
Paul K0UYA
----- Original Message -----
From: "Dave White" <mausoptik@btinternet.com>
To: "Rex Lint" <rex@lint.mv.com>; "Amps" <amps@contesting.com>
Sent: Saturday, March 13, 2010 3:02 PM
Subject: Re: [Amps] Revamping a really ugly amp
> 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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