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AC polarity
AC polarity
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Old 10th September 2012, 11:09 PM   #11
Keriwena is offline Keriwena  United States
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Good info, Jo.

I didn't mean to imply that the two grounds going to the same place in the fusebox was a problem, I just wanted to point out that if you also tie them together on the equipment end, you haven't really achieved anything.
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Old 11th September 2012, 01:12 AM   #12
brilliantblue is offline brilliantblue  United States
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thanks for the info Jo!

I'm not sure on the insulation of the transformer. It appears as solid as any modern transformer I've seen, though it is from the 50's or early 60's. How could I tell if it had paper insulation?

The amp is out of an old Bell & Howell 202 projector, and they hung the transformer in the top of the projector case above the projector and run the wiring through an 11-pin connection.

who here uses the ground breaker in Tauro's post? any luck with it?
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Old 11th September 2012, 06:14 PM   #13
brilliantblue is offline brilliantblue  United States
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whoops - i meant cotton insulation - how could i tell if my transformer has cotton insulation?
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Old 14th September 2012, 03:00 PM   #14
indianajo is offline indianajo  United States
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The best way to detect deteriorated insulation, cotton or whatever, is to isolate the frame from the neutral and put about a 10 k resistor between them. Measure AC voltage across it- that is the leakage current. V/R=I the current. Hammond liked about 40 microamps or less. Ground fault outlets trip at about 140 microamp wikipedia says.
You can see the actual cotton insulation coming out of the transformer on the leads. It has a weave to it. PVC insulation that replaced it is smooth.
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