[AMRadio] RCA Transformer ID?


Bill Guyger bguyger at yahoo.com
Sun Jul 16 20:18:07 EDT 2017


Haven't had a chance to look at these links, I been out in the field at the KTCK transmitter site making adjustments to two of the ATU's with temps in the mid to upper 90's (thankfully my laptop and Network Analyzer didn't crap out because of the heat in the doghouses).

The talk about liberty ships reminded me of an engineer that we had at KLIF when I started working for Susquehanna back in the 80's. He had been a radio operator on liberty ships and told me that his backup transmitter was spark gap. In his 70's back then he could still do 60 wpm cw.

Bill AD5OL 

Sent from my iPhone

> On Jul 16, 2017, at 2:53 PM, C.L. Mitchell <rsq14adam1 at hotmail.com> wrote:
> 
> The only info I have come up with on the Liberty Ship radio gear is here:
> 
> 
> http://jproc.ca/ve3fab/jbradrm.html
> 
> [http://jproc.ca/ve3fab/jbrr1.jpg]<http://jproc.ca/ve3fab/jbradrm.html>
> 
> SS John Brown Radio Room - jproc.ca<http://jproc.ca/ve3fab/jbradrm.html>
> jproc.ca
> S.S. JOHN BROWN RADIO ROOM Liberty ship was the name given to the EC2-S-C1 type ship designed for "Emergency" construction by the United States Maritime Commission in ...
> 
> Mitch, K9PNP
> 
> 
> ________________________________
> From: amradio-bounces at mailman.qth.net <amradio-bounces at mailman.qth.net> on behalf of Donald Chester <k4kyv at charter.net>
> Sent: Saturday, July 15, 2017 10:17 PM
> To: amradio at mailman.qth.net
> Subject: Re: [AMRadio] RCA Transformer ID?
> 
> 
> It's a modulation transformer, but wasn't designed for voice. Thousands of
> them must have been released as surplus after WWII; it may have been the
> most popular modulation transformer for KW rigs in the early 1950s.  It was
> designed by RCA for tone modulated CW (MCW) on Liberty Ships during the war.
> Definitely not broadcast iron, the audio quality is on par with low-cost
> "amateur radio quality" multi-match modulation transformers, such as the UTC
> S-22 and maybe ever the VM- series. They display enough phase shift
> distortion to be visible on a scope when running sine wave tone modulation
> near 100%, but still work pretty well for ham stations.
> 
> One of the drawbacks is the 5500:5500 (one to one) turns ratio.  This causes
> a mis-match with most of the popular modulator tubes, but the distortion
> level is tolerable.  It has a tertiary winding to modulate the screen of a
> tetrode or pentode.  The turns ratio gives good positive modulation peaks if
> the proper modulator tubes are used, for example a quad of 811-As in
> push-pull/parallel.
> 
> The  name plate figures, giving impedance, turns ratio, maximum final
> amplifier plate current through the secondary, plate voltage and modulator
> power rating, don't add up.
> 
> Although zillions of these transformers circulated after the war, very few,
> if any of the transmitter they went into have appeared on  the surplus
> market, or even any descriptions, technical or otherwise of the actual
> transmitters.  It has always been somewhat of a mystery item.
> 
> Don k4kyv
> 
>> -----Original Message-----
>> From: amradio-bounces at mailman.qth.net [mailto:amradio-
>> bounces at mailman.qth.net] On Behalf Of Mike Durff via AMRadio
>> Sent: Friday, 14 July, 2017 19:39
>> To: amradio at mailman.qth.net
>> Subject: [AMRadio] RCA Transformer ID?
>> 
>> RCA 901765-501 Tag says:Class = ModulationPri= 5500 ohmssec = 5500 ohms.
>> I thought it was a modulation transformer, but others say no. Google
>> doesn't yield  conclusive results.
>> Any guesses?
>> Thanks, Durff
>> __________________________________________________________
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> 
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