OK - a little follow up. I asked Duane Wilson who worked in Izenour's lab and is generally pretty knowledgeable about
theatre technology. I suspect he serviced the GCI thyratron tube dimming
system in the Ex at Yale. I asked:
"...got into a discussion of thyratron dimmers. It seems that some thyratron tube dimmers were actually using the tube to control the saturation coil in a mag amp
dimmer. I thought the Izenour thyratron actually controlled the
power – but it’s a little vague trying to google this. I assume they did work at high
voltage and lower
current, requiring a
transformer for the feed and individual transformers for the outputs?"
and Duane replied:
"Yes, both schemes of thyatron control were used. The use to control saturation in a
transformer, a mag amp it was called, was developed in the US by GE and until the late 70's Radio City Music
Hall used the GE mag amp design. These thyratons were small radio tube sized. That scheme was used from about 1932-33 into the 1950's. I know of a theater in Hobbs, NM that had mag amps still in use in the 60's that were installed late 50's..
The GCI scheme was to use the thyraton to directly control the
current, possible because between the early 30's and 39, larger thyratrons became available. These were used to control heat lamps for baking auto finishes in the body factories among other things. There was no load
transformer in the GCI design, the tubes controlled the
current to the load directly, just like SCRs. The GCI design did use small transformers on the control side. Because of the
voltage drop across the tubes, you did have to have a large
transformer ahead of the
dimmer rack that was tapped to provide a
line voltage of about 135-140 volts AC."
