[AMRadio] Mod Transformer Available


Paul Sokoloff dogfaces at comcast.net
Mon Sep 26 21:58:12 EDT 2005


The model number is RCA 901769-501 and it has the original paperwork with
it.  It says that the secondary current is .198 amperes, so I guess you need
2,500 volts to get 500 watts??  There was a page on the internet that said
max current for this beast is 450 ma., so I don't know if that is a
practical and not theoretical conclusion.  Thanks for looking.

Paul

----- Original Message ----- 
From: "James M. Walker" <chejmw at acsu.buffalo.edu>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Monday, September 26, 2005 3:40 PM
Subject: Re: [AMRadio] Mod Transformer Available


> 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.
> Jim
> WB2FCN
>
> ----- 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
> for
> > >sale.  It has 5700 (approx.) ohm P-P primary and a 5700 ohm secondary.
I
> > >would like $250 plus shipping.  Local  pickup near Philadelphia
> preferred.
> > >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
> good
> > 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
> phone
> > 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
> modulating
> > 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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> >
> >
>
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