[AMRadio] Ferroresonant transformer revisited

John Coleman ARS WA5BXO wa5bxo2005 at pctechref.com
Sun May 7 11:28:36 EDT 2006

	Zenith, GE, and Sylvania TV (older tube versions) sets used the
Ferro resonant transformer or Constant Voltage Transformer (CVT) that had a
special winding with about a 1 to 4mf capacitor across it to saturate the
core.  This was there answer to the problems of picture shrinkage when
people's air conditioner kicked on.  They still needed a HV regulator to
prevent blooming when the brightness was turned up.  The CVT regulated the
output voltage for input voltage changes but did not regulate much against
load changes.  These things are used by carpenters when they need to run a
circular electric saw in an area where they need 100ft of extension cord to
get power to the saw. When the saw bogs down in wood it draws more current
and the extension cord would drop 20 volts or more.  The CVT would be placed
at the end of the extension cord and the saw plugged into the CVT.  The
current will drop on the extension cord to 90V but the CVT would hold the
voltage up to 120 on the saw.  

	I found these devices to be very useful in the shack to run the
receiver and XMIT VFO. I always had to retune the receiver after
transmitting and the VFO would drift slightly during XMIT because of the
slight filament voltage drop.  So I ran separate filament XFMR for the VFO
and plugged it into the CVT and ran the receiver from the CVT as well.  This
ended both problems.  I made my CVT from one of the old TV set transformers.
One of the manufactures even put theirs on a separate chassis which made it
easy for me.  These XFMRS had cooling fins around the core and they did get
hot.  At the time, the US was not into the conservation mode.

Here is a google link to a bunch of good info.  

SOLO was a major manufacturer of the ones used by carpenters.


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