View Single Post
Old 8th Feb 2018, 10:30 am   #15
Heatercathodeshort
Dekatron
 
Heatercathodeshort's Avatar
 
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
Default Re: GEC BT336 possible tube change

The clue here is that the width is short and I guess it gets worse with time? Can you also measure the EHT as well as the H.T.?
As Stephen has posted, the old finned rectifier will definitely be U/S that is if it has not been replaced by a silicon diode and 25 ohm 10 watt resistor.

Did you reposition the lin sleeve between the neck and the scan coils when you changed the tube? It may be jammed inside the coils. If in doubt, as a test, simply remove it completely.

It is possible that the snake effect is due to a slight heater cathode leak in the line oscillator or output valve. I will have a look at the circuit later.

The deterioration over time points at the LOPT overwind, the old problem encountered many times on this forum. I have had a similar problem with the earlier but very similar BT302 series but they have always responded, over a couple of days, to the pass a low current through the pitch insulated overwind in an attempt to drive out the moisture. John.
Heatercathodeshort is offline