CRT Base Repair? - UK Vintage Radio Repair and Restoration Discussion Forum

simonsradio · 15th May 2011, 7:09 pm

I am wondering if anyone has any experience of, a technique for, this...

In my "to do" pile is a pretty good EKCO TC209. With no work yet done, the radio works and there is a healthy line whistle and illumination of the U26. It has a replacement (plastic sleeved) HT smoother but otherwise looks pretty untouched.

Unfortunately before I acquired the set it had had a good bash at the back and the CRM 171 CRT base is smashed. The vacuum is intact, the big problem is that one of the heater wires is broken off at the glass

. Otherwise all is easily repairable.

I was thinking (with suitable precautions) of trying to pick away at the glass round the remains of the wire to try to expose enough to make a sufficiently robust connection. Does anyone have any experience and/or success stories of this sort of thing? Or any other tricks - maybe using conductive paint to make a connection, or anything like that? I'd be grateful for any ideas...

(Just before anyone asks - I shorted out the tube heater connections on the connector to do the tests above!)

DangerMan · 15th May 2011, 8:48 pm

If you were to drill a clearance hole through the tube base connector, so that it comes out the back, it might then be possible to poke a pin or something similar through it and make contact to the stump without picking at the glass and risking a nasty hissing sound.
You will need to improvise a spring arrangement to maintain contact pressure.
I once did this with a brand new A63-11X which had had a similar mishap in a Bush CTV25 and had several pins broken off below the surface of the glass. The tube lived to be a great age afterwards with a good picture, but the broken pins were grids and cathodes, not heater pins.
I used ordinary sewing pins but for the heaters you might have to check these don't get hot at the contact point or maybe find a better material. Brass pins are available, I'm sure. You could always reinforce this with a dot of silver loaded paint during assembly if need be.
I used the solder tags on the socket itself to anchor the springs which were actually cut from the earthing contacts of an old variable capacitor.

Pete

Kilham1 · 15th May 2011, 9:24 pm

Either glue a pin/wire in place with conductive silver epoxy (expensive for just one pin and may not handle the current) or fit a spring probe into the base socket, something like this:

http://uk.farnell.com/feinmetall/f11...act/dp/1313692

Alistair D · 15th May 2011, 9:27 pm

To follow on from what Pete said, at work I used to use large numbers of spring loaded test probes to make contact to the test pads on the underside of PCBs. These come in all sorts of diameters and head styles. Fron what you are describing I think they may have a use here.

Have a look at this site

http://www.coda-systems.co.uk/catalog/index.html

I am sure that CPC stocked some as well.

Al

murphyv310 · 15th May 2011, 9:37 pm

Hi.
The spring loaded probe is the best idea, Conductive adhesive although very good may have sufficient resistance and thus heat to crack the glass. Personally I would try to get the CRT in a suitable way working to test, if good then do a permanent repair or look out for another good tube!

simonsradio · 21st May 2011, 11:08 am

Thanks all for those thoughts. I've just ordered a couple of spring loaded probes and will have a play when time permits...

15th May 2011, 7:09 pm	#1
simonsradio Tetrode Join Date: Jul 2007 Location: Chippenham, Wiltshire, UK. Posts: 90	CRT Base Repair? I am wondering if anyone has any experience of, a technique for, this... In my "to do" pile is a pretty good EKCO TC209. With no work yet done, the radio works and there is a healthy line whistle and illumination of the U26. It has a replacement (plastic sleeved) HT smoother but otherwise looks pretty untouched. Unfortunately before I acquired the set it had had a good bash at the back and the CRM 171 CRT base is smashed. The vacuum is intact, the big problem is that one of the heater wires is broken off at the glass . Otherwise all is easily repairable. I was thinking (with suitable precautions) of trying to pick away at the glass round the remains of the wire to try to expose enough to make a sufficiently robust connection. Does anyone have any experience and/or success stories of this sort of thing? Or any other tricks - maybe using conductive paint to make a connection, or anything like that? I'd be grateful for any ideas... (Just before anyone asks - I shorted out the tube heater connections on the connector to do the tests above!) __________________ "I need someone to protect me from all the measures they take to protect me..."

15th May 2011, 8:48 pm	#2
DangerMan Heptode Join Date: Jul 2009 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 719	Re: CRT Base Repair? If you were to drill a clearance hole through the tube base connector, so that it comes out the back, it might then be possible to poke a pin or something similar through it and make contact to the stump without picking at the glass and risking a nasty hissing sound. You will need to improvise a spring arrangement to maintain contact pressure. I once did this with a brand new A63-11X which had had a similar mishap in a Bush CTV25 and had several pins broken off below the surface of the glass. The tube lived to be a great age afterwards with a good picture, but the broken pins were grids and cathodes, not heater pins. I used ordinary sewing pins but for the heaters you might have to check these don't get hot at the contact point or maybe find a better material. Brass pins are available, I'm sure. You could always reinforce this with a dot of silver loaded paint during assembly if need be. I used the solder tags on the socket itself to anchor the springs which were actually cut from the earthing contacts of an old variable capacitor. Pete

15th May 2011, 9:24 pm	#3
Kilham1 Retired Dormant Member Join Date: Apr 2010 Location: Kelso Posts: 6	Re: CRT Base Repair? Either glue a pin/wire in place with conductive silver epoxy (expensive for just one pin and may not handle the current) or fit a spring probe into the base socket, something like this: http://uk.farnell.com/feinmetall/f11...act/dp/1313692

15th May 2011, 9:27 pm	#4
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: CRT Base Repair? To follow on from what Pete said, at work I used to use large numbers of spring loaded test probes to make contact to the test pads on the underside of PCBs. These come in all sorts of diameters and head styles. Fron what you are describing I think they may have a use here. Have a look at this site http://www.coda-systems.co.uk/catalog/index.html I am sure that CPC stocked some as well. Al __________________ I won't tell you how I discovered that.

15th May 2011, 9:37 pm	#5
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: CRT Base Repair? Hi. The spring loaded probe is the best idea, Conductive adhesive although very good may have sufficient resistance and thus heat to crack the glass. Personally I would try to get the CRT in a suitable way working to test, if good then do a permanent repair or look out for another good tube! __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

21st May 2011, 11:08 am	#6
simonsradio Tetrode Join Date: Jul 2007 Location: Chippenham, Wiltshire, UK. Posts: 90	Re: CRT Base Repair? Thanks all for those thoughts. I've just ordered a couple of spring loaded probes and will have a play when time permits... __________________ "I need someone to protect me from all the measures they take to protect me..."