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Heatercathodeshort · 9th Feb 2007, 8:38 pm

Hello Trevor,
I think Jeffrey has got it on the spot. With mains eht the usual problem is breakdown of the transformer. Usually this is spectacularm with arcing and smoke together with wax or tar bubbling from the windings. Small breaks in the eht winding will induce flashover with again the fireworks.

If the Visconol is leaking it will get quite warm and will fail completely after a short period. Mains eht takes no prisoners. It could go O/C but I have never known this, always S/C or leaky. HVR2's are a very good valve and most mains eht sets using them still have their originals in good condition. Failure usually results in its appearance changing to that of a neon lamp....

It's worth checking any series smoothing resistor that may be between the two EHT caps, if it uses two, that is.

You must be very careful and after unplugging the mains; short circuit the eht supply [both caps] and leave the shorting links in place while doing your tests. Only remove the links when you are sure that NO PART of the eht system retains a charge. There is usually a bleeder chain of resistors across the supply that will discharge the capacitors after a short period, but faults in these or the circuit will prevent this.

You will have to take voltage checks with an EHT meter but I don't know how familiar you are with these circuits, so would advise against this until you know the score!

Regards

John.

9th Feb 2007, 8:38 pm	#5
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: EHT problem Hello Trevor, I think Jeffrey has got it on the spot. With mains eht the usual problem is breakdown of the transformer. Usually this is spectacularm with arcing and smoke together with wax or tar bubbling from the windings. Small breaks in the eht winding will induce flashover with again the fireworks. If the Visconol is leaking it will get quite warm and will fail completely after a short period. Mains eht takes no prisoners. It could go O/C but I have never known this, always S/C or leaky. HVR2's are a very good valve and most mains eht sets using them still have their originals in good condition. Failure usually results in its appearance changing to that of a neon lamp.... It's worth checking any series smoothing resistor that may be between the two EHT caps, if it uses two, that is. You must be very careful and after unplugging the mains; short circuit the eht supply [both caps] and leave the shorting links in place while doing your tests. Only remove the links when you are sure that NO PART of the eht system retains a charge. There is usually a bleeder chain of resistors across the supply that will discharge the capacitors after a short period, but faults in these or the circuit will prevent this. You will have to take voltage checks with an EHT meter but I don't know how familiar you are with these circuits, so would advise against this until you know the score! Regards John. Last edited by Mike Phelan; 3rd Nov 2007 at 11:47 am. Reason: Breathless!