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Old 12th Feb 2018, 7:43 pm   #25
Heatercathodeshort
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Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: GEC BT336 possible tube change

You really need a variable power supply typically 0-30v at maybe an amp. Connect it to the EHT overwind, that is the line output valve anode [top cap] to the anode of the EHT rectifier.

Switch on the power supply and increase the voltage until around 30m/a passes through the winding. Test it with your finger after about 30 mins, it needs to be just warm. You can vary the voltage to obtain the best overall result.

Once the temperature is stable you need to leave it connected for a couple of days. DO NOT hurry this procedure and let it 'cook'. Test after two days and if there is an improvement, do the same thing for another two days. Remember it took nearly 40 years to suck in the dampness so patience must be observed.

I would not suggest you attempt to dry it out by operating the chassis for extended periods. The transformer may break down requiring a rewind.

I would suggest you obtain a few essential tools if you want to expand your vintage interests. A variable bench power supply, an EHT meter 0-30kv or 0-20kv if you are sticking to monochrome, a signal generator [nothing fussy] and a simple scope.

All of these items appear at BVWS auctions at very low prices or of course you can visit on line auctions but at the BVWS meets you can actually get hands on before purchase.

These few items will make life a lot easier. I presume you have a reasonable meter of course. Regards, John.
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