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IIIa Parts / tube number

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#1 DavidWest


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Posted 18 August 2004 - 01:18 AM

does anyone know the number on the focus tube in the IIIa ??

also, does anyone know where to get a new crt??

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#2 Ben Fisher

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Posted 18 August 2004 - 05:28 AM

The part is (typically) a: NL-7235 made by National Electronics or Mu.

Chelmer ValveRichardson Electronics

One of these reasons these tubes cook is that the voltage regulation to the heater is not very good. This is why when you use a fresh battery and flick the monitor from standby to on the CRT focus is out (the heater voltage is too high/hot and the tube characteristics change - although it does settle in). We used to build a focus tube regulator board which was direct replacement for the III/A board - nothing special except we used a low-drop out voltage regulator to drive the heater (at slightly less than 12v) - this was stable and hence the focus didn't change.

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#3 jay kilroy

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Posted 20 September 2004 - 08:21 AM


Is the board still available? I have been having some tube issues myself. I would love to correct it for good.

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