EHT corona discharge cure? - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 3rd May 2017, 11:08 pm

Hi,
I've just repaired an 11" B/W CRT monitor and heard a slight EHT corona coming from the rubber cover over the connection to the tube. I thought a smear of Vaseline under the skirt of the cover might have cured it, but no.
There was originally some blue stuff applied during manufacture but it's dried out and now does nothing.
What can I put on in place of the Vaseline?
Thanks in advance.
Cheers, Pete.

Herald1360 · 3rd May 2017, 11:10 pm

Silicon grease?

Nuvistor · 3rd May 2017, 11:21 pm

Check that the glass around the anode connection as not a track burned in it. If the corona has been occurring over a a period of time it can happen. If that is the case it can be very difficult to repair. The rubber insulator is worth replacing , those can track also.
If the glass and insulator are ok then silicon grease is worth a try, you could also think about this product.
http://www.donberg.ie/descript/e/eht_seal_2.htm

Frank

Terry_VK5TM · 4th May 2017, 3:33 am

Silastic used to be the go to product in one workshop I worked in (of a big multi-national, no less).

Bit of a pain to clean up when you had to replace a tripler at a later stage though.

Terry

Tractorfan · 4th May 2017, 8:53 pm

Hi,
Thanks for your replies.
The discharge is slight and there's no sign of tracking. I'll try some bathroom silicon mastic and, if that doesn't work, I'll replace the anode cap.
Cheers, Pete.

dseymo1 · 4th May 2017, 9:01 pm

Don't use bathroom stuff!
The usual sort gives off acetic acid while curing, which will eventually corrode away the wire, if not the connector. I suspect the acid is conductive enough to make matters worse rather than better anyway.

Terry_VK5TM · 5th May 2017, 1:09 am

You need to use neutral cure stuff - the one that doesn't smell like vinegar.

Terry

ionburn · 5th May 2017, 1:51 pm

My experiences in the past have taught me that the number one thing is that all surfaces are clean and dry. Generally it is a last resort to add additional insulation. If there were some originally then it may well need replacing but the EHT corona does concern me a bit, especially on what is a failrly low voltage B/W set.

ColinTheAmpMan1 · 5th May 2017, 8:14 pm

The stuff you need may be called "Corona Dope". It is available from here https://www.techsil.co.uk/mg-chemica...g-varnish-55ml for £7.50 inclusive of VAT and there's a similar product from Farnell.
Colin.

3rd May 2017, 11:08 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	EHT corona discharge cure? Hi, I've just repaired an 11" B/W CRT monitor and heard a slight EHT corona coming from the rubber cover over the connection to the tube. I thought a smear of Vaseline under the skirt of the cover might have cured it, but no. There was originally some blue stuff applied during manufacture but it's dried out and now does nothing. What can I put on in place of the Vaseline? Thanks in advance. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

3rd May 2017, 11:10 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: EHT corona discharge cure? Silicon grease? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

3rd May 2017, 11:21 pm	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: EHT corona discharge cure? Check that the glass around the anode connection as not a track burned in it. If the corona has been occurring over a a period of time it can happen. If that is the case it can be very difficult to repair. The rubber insulator is worth replacing , those can track also. If the glass and insulator are ok then silicon grease is worth a try, you could also think about this product. http://www.donberg.ie/descript/e/eht_seal_2.htm Frank

4th May 2017, 3:33 am	#4
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,342	Re: EHT corona discharge cure? Silastic used to be the go to product in one workshop I worked in (of a big multi-national, no less). Bit of a pain to clean up when you had to replace a tripler at a later stage though. Terry

4th May 2017, 8:53 pm	#5
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	Re: EHT corona discharge cure? Hi, Thanks for your replies. The discharge is slight and there's no sign of tracking. I'll try some bathroom silicon mastic and, if that doesn't work, I'll replace the anode cap. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

4th May 2017, 9:01 pm	#6
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: EHT corona discharge cure? Don't use bathroom stuff! The usual sort gives off acetic acid while curing, which will eventually corrode away the wire, if not the connector. I suspect the acid is conductive enough to make matters worse rather than better anyway.

5th May 2017, 1:09 am	#7
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,342	Re: EHT corona discharge cure? You need to use neutral cure stuff - the one that doesn't smell like vinegar. Terry

5th May 2017, 1:51 pm	#8
ionburn Heptode Join Date: Dec 2014 Location: Lincoln, Lincolnshire, UK. Posts: 583	Re: EHT corona discharge cure? My experiences in the past have taught me that the number one thing is that all surfaces are clean and dry. Generally it is a last resort to add additional insulation. If there were some originally then it may well need replacing but the EHT corona does concern me a bit, especially on what is a failrly low voltage B/W set.

5th May 2017, 8:14 pm	#9
ColinTheAmpMan1 Octode Join Date: Jan 2012 Location: Wimbledon, London, UK. Posts: 1,465	Re: EHT corona discharge cure? The stuff you need may be called "Corona Dope". It is available from here https://www.techsil.co.uk/mg-chemica...g-varnish-55ml for £7.50 inclusive of VAT and there's a similar product from Farnell. Colin.