Black Paint on HV Windings ?

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k4kyv:
Quote from: Bill, KD0HG on November 01, 2009, 09:27:29 AM

Shouldn't be a concern.

There's only a few volts between turns of even high voltage transformers.




The greatest danger is from arcing over between layers of windings, and between the windings and the core of the transformer.  Also, the manufacturer sometimes failed to sufficiently insulate the leads running to and from the windings, from the rest of the winding and/or the core.  If there is no varnish or other treatment, moisture from the air can degrade the insulation, particularly the kind of paper used in older transformers.  The paper itself degrades over time and becomes brittle and undoubtedly a less perfect insulator even if it is kept dry.

That's why I always float the frame of vintage modulation transformers, modulation reactors and filter chokes away from ground and make sure I am using well insulated mounting hardware.  It is not a good idea to impose unnecessary HV stress on whatever dielectric exists between windings and core.

This should be less a problem with newly constructed transformers.  The insulating materials used to-day are supposed to be far superior to what was used in the WW2 era and before.

kg8lb:
.

Bill, KD0HG:
Here's the dielectric properties of Glyptal transformer varnish.
There's at least a dozen places selling it per Google.

You can also still get Q-Dope and Scotchkote as alternatives.

Typical Glyptal Cured Film Properties:
Dielectric strength—Dry—ASTM 0115-55—volts/mil 1500
Dielectric strength 24 hours in water—volts/mil 350
Arc resistance—seconds 480

 Meets requirements of MIL-E-2218
 Flexibility is far superior to competitive red sealers on both backed and air-dried films. 1201 can take rugged impact.
 Water Resistance is excellent.
 Prolonged Aging doesn’t crack 1201’s film, leaves no place for destructive agents to get in.
 Drying 1201 is tack-free in about 2 hours at room temperature, can be baked to a beautiful smooth finish.
 Heat Resistance. 1201 has got it, can withstand continuous 135°C temperatures.
 Toughness. High-gloss paints have a tender film. 1201 has a low-gloss finish, designed for great resistance to abrasion.
 Adhesion. 1201 hangs on, stays where it’s put—on metals, ceramics, porcelain, concrete, fibres, and wood.

w4bfs:
Quote from: Bill, KD0HG on November 01, 2009, 09:30:38 PM

Here's the dielectric properties of Glyptal transformer varnish.
There's at least a dozen places selling it per Google.

You can also still get Q-Dope and Scotchkote as alternatives.

Typical Glyptal Cured Film Properties:
Dielectric strength—Dry—ASTM 0115-55—volts/mil 1500
Dielectric strength 24 hours in water—volts/mil 350
Arc resistance—seconds 480

 Meets requirements of MIL-E-2218
 Flexibility is far superior to competitive red sealers on both backed and air-dried films. 1201 can take rugged impact.
 Water Resistance is excellent.
 Prolonged Aging doesn’t crack 1201’s film, leaves no place for destructive agents to get in.
 Drying 1201 is tack-free in about 2 hours at room temperature, can be baked to a beautiful smooth finish.
 Heat Resistance. 1201 has got it, can withstand continuous 135°C temperatures.
 Toughness. High-gloss paints have a tender film. 1201 has a low-gloss finish, designed for great resistance to abrasion.
 Adhesion. 1201 hangs on, stays where it’s put—on metals, ceramics, porcelain, concrete, fibres, and wood.



also tried to add Don's quote about Glyptal color .... GE used the stuff ( usually green ) for many years after alignment to keep vibration from shifting settings .... fwiw ...73

AB3L:
Quote from: k4kyv on October 30, 2009, 09:40:42 PM

I  recall there used to be a product called Glyptal, a high voltage paint.  It came in either red or black.  I  would assume the black stuff used something other than carbon black for pigment.  In fact, I tried to find some a few years ago, but all I could find was the red stuff.



I believe that Collins used the red Glyptol on the S-line/ KWM series as a QC marker for solder joints that were checked and approved. I have a 75S-3B loaded with it under the chassis. Perhaps to keep atmosphere from the joints?

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