Murphy V240C Any help whatsoever. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

FERNSEH · 16th Dec 2014, 2:14 am

As far testing the CRT is concerned, an interesting suggestion from JohnHKS is to consider the grid and cathode of the tube as a diode. The grid and leads are removed for this test. Supply the correct heater voltage to the CRT which for the Mazda CRM141 is 12.6 volts, leave the tube running for a while. Using a multimeter switched to the resistance range connect the meter to the grid and cathode pins. If the CRT has any emission this will be indicated as a meter reading. The internal battery supplies the necessary voltage for the conduction test. If there is no reading, reverse the meter leads and try again.

I have never tried this procedure but I'm certain it works.
A few words of caution. The correct heater voltage for the CRM141 is 12.6 volts but some rebuilt tubes were occasionally fitted with 6.3 volt gun assemblies.

DFWB.

andycapp · 16th Dec 2014, 3:07 am

Thanks DFWB

Heatercathodeshort · 16th Dec 2014, 10:55 pm

This is a rough test for 'some' emission. If reading as David has suggested it is likely to produce a picture and may well be OK but not of course a reading of quantity or quality of emission. Makes a good test for an unknown tube and is completely harmless. John.

Freya · 17th Dec 2014, 11:57 am

This is exactly the method used by all Taylor valve testers in conjunction with the CRT adapter.

andycapp · 21st Dec 2014, 11:03 pm

Quote:

Originally Posted by FERNSEH

The circuit diagram of the V240 can be found in the 1955/56 Newnes Radio and television servicing book.

That book arrived yesterday DFWB, very informative reading but will be a lot better when I have read and understood it a few times. I am now trying to find the same books on the Bush TV22s a b c, and also hopefully a few books on my radios, many thanks for the heads up DFWB, regards And a good Christmas, Andy

16th Dec 2014, 2:14 am	#21
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Murphy V240C Any help whatsoever. As far testing the CRT is concerned, an interesting suggestion from JohnHKS is to consider the grid and cathode of the tube as a diode. The grid and leads are removed for this test. Supply the correct heater voltage to the CRT which for the Mazda CRM141 is 12.6 volts, leave the tube running for a while. Using a multimeter switched to the resistance range connect the meter to the grid and cathode pins. If the CRT has any emission this will be indicated as a meter reading. The internal battery supplies the necessary voltage for the conduction test. If there is no reading, reverse the meter leads and try again. I have never tried this procedure but I'm certain it works. A few words of caution. The correct heater voltage for the CRM141 is 12.6 volts but some rebuilt tubes were occasionally fitted with 6.3 volt gun assemblies. DFWB.

16th Dec 2014, 3:07 am	#22
andycapp Retired Dormant Member Join Date: Aug 2014 Location: Bath, Avon, UK Posts: 235	Re: Murphy V240C Any help whatsoever. Thanks DFWB

16th Dec 2014, 10:55 pm	#23
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Murphy V240C Any help whatsoever. This is a rough test for 'some' emission. If reading as David has suggested it is likely to produce a picture and may well be OK but not of course a reading of quantity or quality of emission. Makes a good test for an unknown tube and is completely harmless. John.

17th Dec 2014, 11:57 am	#24
Freya Octode Join Date: Jan 2009 Location: Falmouth, Cornwall, UK. Posts: 1,989	Re: Murphy V240C Any help whatsoever. This is exactly the method used by all Taylor valve testers in conjunction with the CRT adapter. __________________ Stephen _________"It`s only an old telly" ___