|[AMRadio] Mod Transformer Available|
w5omr at satx.rr.com
Sun Sep 25 23:21:22 EDT 2005
Paul Sokoloff wrote:
> 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
Sounds like an old Liberty Ship MCW transmitter mod transformer.
Typically, those that I've seen were 1:1 @ 5,500 Ohms of Impedance.
These old buzzard transformers have been around for a good long time,
and were plentiful, and easily had, at one time. I think there's still
a lot of 'em around, but they're doing duty more as a door stop. Lots
of folks don't use 'em, because of the plate on the secondary, that says
"MAX 0.200 AMP DC".
Don/K4KYV wrote a nice article in here a while back about the liberty
ship transmitters and their MCW modulation transformers, that had screen
windings on them.
I never did quite understand if the 200mA on the secondary was the
Maximum current it could take, or if 200mA was the max, before the core
K5SWK ran/runs one of these on a pair of 833's. I ran a pair of
250TH's on one, but would never draw more than 200mA in the final...
more than that, the audio response was severly restricted, until I
strung some chokes together to shunt the DC off of the modulation
transformer secondary. 3000v @ 300mA. Life was good, for a while.
73 = Best RegardS
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