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[TCML] Unexpected NST behavior

I am building a project using a NST. The NST is an old-style one with an iron core. It is an Acme Electric rated for 12 KV at 30 ma. What seems unusual to me is that I can draw an arc from either HV terminal to an earth ground. This is with the case floating so there doesn't appear to be a complete circuit to allow this to happen. Can anyone explain this? I want to connect one of the HV terminals to an earth ground (after rectification and filtering) and leave the case floating but this odd behavior is preventing this. When I try to do this, the NST appears to be shorted to ground even though the case is floating. I tried a different NST and got the same behavior.

I also notice that when I measure the voltage with no load, I get a DC value of 20 KV. This is with a full wave bridge rectifier and a 400 pF filter capacitor. I have read that NSTs are designed to initially output a higher than normal voltage to start a neon tube. Is this what I am seeing? I expected to see about 17 KV DC (1.414 x 12000).

Steve White
Cedar Rapids, Iowa
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