CRM121B wanted - heater O/C - can it be fixed? - UK Vintage Radio Repair and Restoration Discussion Forum

grindrod · 23rd Mar 2005, 9:58 pm

Hello everyone in proper TV land, thanks to everyone who has helped so far in getting my T161 back to life, sadly the tube heater no longer wants to play so I am looking for a CRM121B if anyone has a working one going spare.

My definition of 'proper tv' is B&W with a comforting whistle, occaisional frame slip and a space behind the sofa to take refuge from the Daleks!! I hope you all agree!!!

Regards, Martin, staring at a blank screen but at least the TV12a is working!

grindrod · 24th Mar 2005, 2:47 pm

Hi Trevor and Darius, the Murphy looks like a good project!! The problem with my tube heater is that it has developed a break.

What I have found is that if I apply a variable voltage that is current limited to 1.3A (the heater is 2V 1.3A) and watch the heater current then as I increase the voltage from zero, no current flows, at 50V or so some current starts to flow which sometimes will increase up to the 1.3A limit at the same time the voltage drops down to 2V and the heater glows normally.

If I switch off and let the heater cool it then becomes open circuit again and I have to repeat the operation.

Applying the current limited higher voltage must jump the break and create a temporary join that lasts while the heater is hot.

Regards, Martin

oldeurope · 24th Mar 2005, 5:01 pm

Maybe the wire in the bakelite socket is not well soldered.
Did you check this out?

Darius

Danny · 25th Mar 2005, 12:32 am

Hi
It is worth re sweating the heater pins, as I have had this happen also.

I read an article in a Practical Television on welding heaters using a charged cap; I can't remember the date of the mag, though.

Tubes are going to be a real problem soon. I don't know of any regunners that would do tubes.

grindrod · 25th Mar 2005, 10:13 am

Hi everybody, the tube base was loose so I unsoldered it and made direct connection to the leads.

By applying a high AC voltage with a current limiting resistor I can achieve a temporary weld, I understand that there was a piece of service kit available years ago that did something similar.

I have nothing to loose with this tube so I will try a few experiments to see if I can achieve a permanent weld. Watch this space for results!!!

Regards, Martin

mickjjo · 25th Mar 2005, 10:38 am

This looks like the article Danny was referring to:-

http://www.thevalvepage.com/teletech/crt_oc/crt_oc.htm

Good luck!

.

Regards, Mick.

grindrod · 26th Mar 2005, 9:00 pm

Hi everyone, I have a mains transformer with a 3kV secondary that was going to be used in a home brew HF linear amp that I never got round to building!! It was last used to locate a break in my dads under-floor heating cable, we attached it through a large value resistor and used a transistor radio to pinpoint the arc, we located the break to within a few inches!!

I will rig up a similar setup to see if I can make a weld!!

Watch this space!!

Martin

23rd Mar 2005, 9:58 pm	#1
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	CRM121B wanted - heater O/C - can it be fixed? Hello everyone in proper TV land, thanks to everyone who has helped so far in getting my T161 back to life, sadly the tube heater no longer wants to play so I am looking for a CRM121B if anyone has a working one going spare. My definition of 'proper tv' is B&W with a comforting whistle, occaisional frame slip and a space behind the sofa to take refuge from the Daleks!! I hope you all agree!!! Regards, Martin, staring at a blank screen but at least the TV12a is working!

24th Mar 2005, 2:47 pm	#2
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: CRM121B Wanted Hi Trevor and Darius, the Murphy looks like a good project!! The problem with my tube heater is that it has developed a break. What I have found is that if I apply a variable voltage that is current limited to 1.3A (the heater is 2V 1.3A) and watch the heater current then as I increase the voltage from zero, no current flows, at 50V or so some current starts to flow which sometimes will increase up to the 1.3A limit at the same time the voltage drops down to 2V and the heater glows normally. If I switch off and let the heater cool it then becomes open circuit again and I have to repeat the operation. Applying the current limited higher voltage must jump the break and create a temporary join that lasts while the heater is hot. Regards, Martin

24th Mar 2005, 5:01 pm	#3
oldeurope Retired Dormant Member Join Date: Dec 2003 Location: Solingen, Germany Posts: 727	Re: CRM121B Wanted Maybe the wire in the bakelite socket is not well soldered. Did you check this out? Darius

25th Mar 2005, 12:32 am	#4
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: CRM121B Wanted Hi It is worth re sweating the heater pins, as I have had this happen also. I read an article in a Practical Television on welding heaters using a charged cap; I can't remember the date of the mag, though. Tubes are going to be a real problem soon. I don't know of any regunners that would do tubes. Last edited by Mike Phelan; 19th Jun 2007 at 12:09 pm. Reason: Tidy-up for archive

25th Mar 2005, 10:13 am	#5
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: CRM121B Wanted Hi everybody, the tube base was loose so I unsoldered it and made direct connection to the leads. By applying a high AC voltage with a current limiting resistor I can achieve a temporary weld, I understand that there was a piece of service kit available years ago that did something similar. I have nothing to loose with this tube so I will try a few experiments to see if I can achieve a permanent weld. Watch this space for results!!! Regards, Martin

25th Mar 2005, 10:38 am	#6
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	Re: CRM121B Wanted This looks like the article Danny was referring to:- http://www.thevalvepage.com/teletech/crt_oc/crt_oc.htm Good luck! . Regards, Mick.

26th Mar 2005, 9:00 pm	#7
grindrod Retired Dormant Member Join Date: Feb 2005 Location: Stroud, Gloucestershire, UK. Posts: 57	Re: CRM121B Wanted Hi everyone, I have a mains transformer with a 3kV secondary that was going to be used in a home brew HF linear amp that I never got round to building!! It was last used to locate a break in my dads under-floor heating cable, we attached it through a large value resistor and used a transistor radio to pinpoint the arc, we located the break to within a few inches!! I will rig up a similar setup to see if I can make a weld!! Watch this space!! Martin