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Heatercathodeshort · 27th Feb 2018, 3:26 pm

That is good news. Incredible as it may seem the LOPT is probably still 'damp' but extended intermittent use will probably clear the fault. If not it's back to the warming process for another couple of days. It's inset moisture and can be a devil to drive out.

As for your hum problem it could be a heater cathode leak in the line oscillator or timebase valves. You really need a scope for this to trace where it is coming from.
First suspects are the line oscillator valve, sync seperator and the line output valve itself. Scope the HT line and see if it has a 'wiggle', the line drive to the control grid N389. You must be able to see it on the scope. Almost there. John.

27th Feb 2018, 3:26 pm	#38
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: GEC BT336 possible tube change That is good news. Incredible as it may seem the LOPT is probably still 'damp' but extended intermittent use will probably clear the fault. If not it's back to the warming process for another couple of days. It's inset moisture and can be a devil to drive out. As for your hum problem it could be a heater cathode leak in the line oscillator or timebase valves. You really need a scope for this to trace where it is coming from. First suspects are the line oscillator valve, sync seperator and the line output valve itself. Scope the HT line and see if it has a 'wiggle', the line drive to the control grid N389. You must be able to see it on the scope. Almost there. John.