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Heatercathodeshort · 24th Oct 2017, 9:36 am

I still think it is the LOPT overwind that is causing the problem.

The overwind is a pitch insulated assembly that allows moisture to enter and I suspect it also alters it's character. It gave little trouble in it's service life but of course we have moved on 55 years!

Can you measure the actual EHT voltage? I suspect it is dropping with the decrease in width.

The HT supply to the height control is derived from the boost rail stated in the VC1 manual as being 670v. Does this vary?

Reducing the actual H.T. line on my VC1 causes the height and width to reduce due to lack of stabilization of both the boost voltage and the supply to the frame oscillator usually taken care of by a couple of VDRs.

I presume you have used a serviceable capacitor for the boost. C126 .1uf 1000v.

Regards, John.

24th Oct 2017, 9:36 am	#17
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: KB VC1 width problem I still think it is the LOPT overwind that is causing the problem. The overwind is a pitch insulated assembly that allows moisture to enter and I suspect it also alters it's character. It gave little trouble in it's service life but of course we have moved on 55 years! Can you measure the actual EHT voltage? I suspect it is dropping with the decrease in width. The HT supply to the height control is derived from the boost rail stated in the VC1 manual as being 670v. Does this vary? Reducing the actual H.T. line on my VC1 causes the height and width to reduce due to lack of stabilization of both the boost voltage and the supply to the frame oscillator usually taken care of by a couple of VDRs. I presume you have used a serviceable capacitor for the boost. C126 .1uf 1000v. Regards, John.