UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - TV24 Still no picture

Heatercathodeshort · 4th Sep 2007, 7:53 am

O.K. Dom,
It is very unusual to get absolutely nothing in the way of a raster on the screen of a Mullard tube.
If the EY51 is lighting up you should have enough EHT to produce something, if only a glimmer on the CRT face.

First measure the heater volts across pins 1 and 12. It should read around 6volts AC of course but may be very SLIGHTLY under this.
If it only reads around 3-4volts the heater is partially short circuit and a temporary cure can be effected by tipping the set backwards whilst working and gently tap the tube neck three or four times to dislodge the short. It is not a permanent cure and the short will return.

If effective the tube heater will glow noticeably brighter.
Now brutal measures.
Short the control grid and cathode of the tube with a resistor around 2k and try again adjusting the ion trap. It needs to be about a 1/4 of an inch from the tube base. If you have got some eht this must produce a screen illumination. If not the tube may have a disconnected cathode or poor vacuum. Hope these notes are of help.

4th Sep 2007, 7:53 am	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: TV24 Still no picture - knackered tube? O.K. Dom, It is very unusual to get absolutely nothing in the way of a raster on the screen of a Mullard tube. If the EY51 is lighting up you should have enough EHT to produce something, if only a glimmer on the CRT face. First measure the heater volts across pins 1 and 12. It should read around 6volts AC of course but may be very SLIGHTLY under this. If it only reads around 3-4volts the heater is partially short circuit and a temporary cure can be effected by tipping the set backwards whilst working and gently tap the tube neck three or four times to dislodge the short. It is not a permanent cure and the short will return. If effective the tube heater will glow noticeably brighter. Now brutal measures. Short the control grid and cathode of the tube with a resistor around 2k and try again adjusting the ion trap. It needs to be about a 1/4 of an inch from the tube base. If you have got some eht this must produce a screen illumination. If not the tube may have a disconnected cathode or poor vacuum. Hope these notes are of help.