[AMRadio] Mod Transformer Available

James M. Walker chejmw at acsu.buffalo.edu
Mon Sep 26 15:40:53 EDT 2005

I have that transformer as well, it is in the pair of 805
modulator stage for my HB 304TL rig. The system runs at 1500 VDC
For the plate supply to the modulator and also the RF deck.
I rewired the speech amp to a pair of 2A3s to drive the 805s.
I haven't done an audio sweep to check the range yet however.

The ratings are 5500 primary 1.14 KVA, and 5500 secondary
.198 Amp DC.

----- Original Message -----
From: "Donald Chester" <k4kyv at hotmail.com>
To: <amradio at mailman.qth.net>
Sent: Monday, September 26, 2005 3:22 PM
Subject: RE: [AMRadio] Mod Transformer Available

> >     I have a 1940s vintage 500 watt modulation transformer made by RCA
> >sale.  It has 5700 (approx.) ohm P-P primary and a 5700 ohm secondary.  I
> >would like $250 plus shipping.  Local  pickup near Philadelphia
> >I checked the windings and they have continuity.  There is also another
> >winding of a higher impedance maybe for screens.  If interested please
> >contact me directly at dogfaces at comcast.net
> After WW2 those transformers flooded the market as surplus.  You could
> hardly attend a hamfest without seeing at least one.
> They are not broadcast quality, but the quality is probably at least as
> as typical trarsformers sold for ham radio use.
> For years I wondered what they came from or what they were manufactured to
> go into.  A couple of years ago I found out that they were not used in
> transmitters at all, but in tone modulated CW rigs on board Liberty Ships
> during the war.  So they were desgined to pass only a single tone
> frequency, but they work passibly for voice.  I would still prefer a
> transformer designed for voice use, preferably something from a broadcast
> transmitter.
> Don k4kyv
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