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Old 14th Feb 2007, 8:41 pm   #8
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,173
Default Re: Baird T18 - focus problem.

Hi Trevor, take care if you are passing additional current through the coil. The HT rail will probabaly stand it as will the focus coil, but you may notice the focus change as the coil heats up, requiring re-setting of the control.
This is because copper has a high, positive temperature coefficient of resistance.
This has hopefully explained a problem before you have seen it. Some 405 sets had a thernistor (NTC) in series with the frame coils to prevent height variations during warm-up and operation.

Ed
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