It was a great idea! The pot was not the problem.
In the same vein I tried shorting the 2 100Ω resistors in the cathode chain and that made no difference either.
I tried replacing the screen to cathode resistor, again no change.
I then replaced the 900Ω and 100Ω resistors with a 1K 1W resistor which was all I had but calculated to be sufficient.
A weird thing happened. The problem got worse for a few seconds and then pretty much disappeared.
I returned the original resistors, removing the old solder and added new and hey presto, no noise!
The problem was an old solder joint that looked OK but wasn't!
Thanks all for your help. This process of elimination has been most instructive.
Dave.
Pleased to hear it was a dodgy solder joint. The worst to find but a lesson learnt, not to replace things indiscriminately as you may end up missing the fault completely and get totally confused by introducing more issues.
Keep a level head and all will be fine.
I used to say to my engineers, when they got stressed with a fault repairing TV sets,"It's only a telly".
Keep a level head and all will be fine.
I used to say to my engineers, when they got stressed with a fault repairing TV sets,"It's only a telly".
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