[TCML] Old TC restoration advice

[David Speck <Dave@xxxxxxxxxxxxxxxx>]

Esteemed list,

Halloween is rapidly approaching, and I find myself with no working TC 
to demo to the Trick or Treaters.  Looks like the weather will be good 
this year, so I can't use rain and snow as an excuse for not having a 
working coil.

My best prospect for quick repair is a vintage coil that I bought from 
the late Harry Goldman a few years (~15) back.  It has an ~4" x ~16 
secondary, a 14" toroid, and a flat 12" pancake primary, and an 
asynchronous RSG.  It ran beautifully until an overenthusiastic 
assistant let it run a bit too long and burned out one of the unobtanium 
transformers (open secondary).

It was driven by a series pair of exotic ex-military radar transformers, 
supplying about 10 kVAC.  I'm not sure of the available current.  These 
transformers were apparently self-ballasting, like a NST, and the coil 
never used a separate ballast.

The transformers are featureless black epoxy cubes, without any 
identifying designation.  These blocks fit loosely about a continuous 
core made from a single strip of flat transformer steel wound into a 
square shape.  I still can't figure out how they were built.

I tried replacing the bad transformer with a 9 kV 30 mA NST, but the 
coil runs very rough.  Not having a Terry filter in place, I didn't let 
it run for more than a couple of seconds.  I have the parts for a Terry 
filter, and have the assembly nearly complete.

A thought occurred to me, though, that somewhere I recalled that NSTs 
generally don't work well with async RSGs.  Converting the ASRG to a 
synchronous RSG on short notice is not likely doable.

So my question is:  On short notice, would I be better off finishing the 
Terry filter, and trying one or two parallel 9 kV NSTs and retuning the 
primary,

Or,

Should I throw together an 8.8 kV four MOT stack and use an external 
ballast?

Any suggestions will be appreciated.

Thanks,

Dave


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