[AMRadio] RE: Seeking advice on testing modulation transformers


Donald Chester k4kyv at hotmail.com
Sun Sep 24 00:28:31 EDT 2006


>   By the way, does anyone have any experience using the RCA 5500  5500 
>units?


They are about the same quality audio-wise as typical  ham radio quality mod 
transformers such as the UTC S- series, or the Thordarson or Stancor 
"universal" transformers.  Not as good as the UTC CVM series.  Definitely 
not broadcast quality.

I have tried a couple of them out, and found the low end frequency response 
to be lacking, and phase shift distortion to be obvious by just looking at 
the envelope pattern.

Those transformers were not designed for voice modulation, but rather, 
single tone modulation.  They were built for tone modulated CW use during 
WW2 on Liberty Ships.

The voltage, impedance and power ratings listed on the nameplate do not add 
up mathematically.

They will work ok if you have a modulator that will work into a fairly low 
plate-to-plate load impedance, such as a quad of tubes in pushpull-parallel. 
  The 1:1 turns ratio should allow for very good positive peaks.  But don't 
be surprised to see visible waveform distortion on the envelope pattern with 
the scope.





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