barrie at centric.net
Sat Dec 1 17:12:54 EST 2007
----- Original Message -----
From: "jeremy-ca" <km1h at jeremy.mv.com>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Saturday, December 01, 2007 2:45 PM
Subject: Re: [AMRadio] Building
> ----- Original Message -----
> From: "Barrie Smith" <barrie at centric.net>
> To: "Discussion of AM Radio" <amradio at mailman.qth.net>
> Sent: Saturday, December 01, 2007 2:27 PM
> Subject: [AMRadio] Building
> Well, I was building a new HV power supply, until I had my gallbladder
> taken out last week! Not supposed to lift anything over 20 lbs for a
> It's a resonant-choke supply. I was just to the point (with a bunch of
> taking out and putting in of parts) of drilling the mounting holes and
> finishing it up.
> Now (due to a wonderful fellow on this list, whom I'll name if I get
> permission), I'm going to start working on an RF deck using a pair of
> These tubes are a cross between a 100TH and the 250TH in a small,
> strangely-shaped envelope. Should be just right for 300 easy watts out.
> They are a 100TH repackaged for radar use in WW2 and use a 250TH filament
> for sustained peak emission. It was also designated the 100TS by Eimac.
> An OT ham down the street from me in the 50's ran a pair at 1KW input on
> 20 CW, it was fun watching those plates glow!
> Now I'm thinking about a modulator.
> Why not 2 more 127A's? With a window in the rack panel you can watch the
> plate color with modulation.
Carl: Thanks for the response.
Well, I did think of that, but I'm kind of at loose-ends here as to what to
do about a moulation transformer.
I have four modulation transformers in the junk box. One is a very
conservative KW PWD, which is large and heavy (I used that in a PP pair of
450THs, modulated by a pair of 304TLs, a long time ago. That transmitter
made a heap-of-smoke . . . and RFI). Another is a National that says 70
watts. It came out of an FAA transmitter, built by National, that used a
pair of 4-65As in the final.
I also have a modulation trasformer that came out of a 250 watt Gates BC
transmitter. And, a Thermadore, that I can't seem to find any information
The KW PWD is rated for 800 watts audio 40 to 7500 hz. It has no air-gap,
and is to be used with a matching reactor and cap, which I have.
The primary is 12,000 ohms, center-tapped. The secondary is 4545 ohms.
I'm mentioning these figures because it's been at least 15 years since I've
calculated various tubes and voltages for matching up modulation tubes and
I do remember that on the 450THs I was running 2500 volts @ 600 ma. Don't
remember what the modulation voltage was.
73, Barrie, W7ALW
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