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High Voltage Potting
Original poster: "Steve Burgess by way of Terry Fritz <twftesla-at-qwest-dot-net>" <SBURGESS-at-Channel4.co.uk>
I was interested to read your thoughts on HV potting:
I need to build a replacement tripler (voltage multiplier in the manner of
Cockcroft-Walton) for a failed unit in a high quality 16x9 aspect ratio
(widescreen) television monitor I have. It will use 6 HV diodes (eg BY8418)
and 5 1000pF/15kV caps - plus 15 HV resistors connected in series to bleed
100 microamps from the 28kV EHT output which goes to the CRT's final anode.
This bleed current is fed back to stabilise the 28kV (and thus picture size)
against variations in beam current.
I plan to pot in a 100 x 50 x 25mm ABS plastic potting box and will use a
couple of small polypropylene sheets to string the diodes and resistors
between, with the caps on the outside. I'll pot flying wires for the
ground, first-stage focus volts take-off, the EHT out and the bleed current
- and a pin to take the 9.5kV input pulse wire from the step-up transformer.
I knocked-up a 'free-air' doubler recently which gave 20kV - and the odd
spark and bang, so the need for encapsulation obvious!
Maybe you can answer some questions for me:
Which type of wax should I use?
What's a double boiler?
Is ABS plastic OK with the wax-and-polyethylene-strip mix at pouring
Is the mix good for not fracturing with movement at wire lead-outs?
How good is the method at eliminating air (to avoid corona)?
Hope you can help.
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