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Old 30th Aug 2019, 4:41 pm   #190
FERNSEH
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Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 5,975
Default Re: Baird T5 restoration project.

Hello Jac,
It's all too evident that there is an inter-electrode leak in the CRT.
However, I think I can do something about the matter without changing the tube. It's unlikely a another good Cossor 3265 or 65K will ever turn up again and there is absolutely no chance whatsoever of finding a Cathodevisor 15MW1.

A 0 - 30 volt bench power supply has been hooked up the grid and cathode of the tube. Result, almost complete visual cut off with -30volts applied to the grid. So it follows if the CRT gun can be supplied from low resistance sources it will be possible to continue to using the same tube. In the Baird T20 the brightness control function is implemented by varying the CRT cathode voltage. The positive going video is supplied to the grid as it is in the T5.
Unfortunately for me the tube cathode is connected at the base to one of the heater pins, so in order to remove the wire link the tube will have to come out again. Taking a tube out of a T5 or T23 is easy, just disconnect the wires to the base sockets, remove the EHT connector and just lift the tube out vertically and away from the cabinet. Simples.
Refitting the tube is bit more scary though, although in a sense it is the reversal of removing it.
Let's see if there are any alternative means of using this tube without too many modifications to the set.

DFWB.

Last edited by FERNSEH; 30th Aug 2019 at 4:49 pm.
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