Ok - I have tried the cans and they don't unfortunately make any difference. Either earthed or left alone.
I have finished shielding the DC heater cables, and this has probably removed 40-50% of hum, I am going to fit a steel plate earthed to the chassis to help isolate the transformer further from the line stage valves, which when tried roughly by hand made a small difference.
I am also trying to clean the bases.
After that I am lost to try and find where this hum is coming from, so any more ideas - yes please!
I have finished shielding the DC heater cables, and this has probably removed 40-50% of hum, I am going to fit a steel plate earthed to the chassis to help isolate the transformer further from the line stage valves, which when tried roughly by hand made a small difference.
I am also trying to clean the bases.
After that I am lost to try and find where this hum is coming from, so any more ideas - yes please!
I had this fault on something I repaired over 50 years ago but I am racking my brains to remember what I did to cure it.
In radio communications steel plates were used to separate the sensitive RF section from the rest and transformers were always a distance away from the input aerial ( antenna ) connection .
A can can be made to shroud the transformer but it must be earthed and also changing the angle of the transformer ( swiveling it ) can help.
Have a read of this PDF by Kemet capacitor design engineers in relation to stacked multi layer ceramic capacitors ( class 2 and class 3 ) producing noise/buzzing etc -
https://sh.kemet.com/Lists/Technica... Reduced Microphonics and Sound Emissions.pdf
In radio communications steel plates were used to separate the sensitive RF section from the rest and transformers were always a distance away from the input aerial ( antenna ) connection .
A can can be made to shroud the transformer but it must be earthed and also changing the angle of the transformer ( swiveling it ) can help.
Have a read of this PDF by Kemet capacitor design engineers in relation to stacked multi layer ceramic capacitors ( class 2 and class 3 ) producing noise/buzzing etc -
https://sh.kemet.com/Lists/Technica... Reduced Microphonics and Sound Emissions.pdf
more progress
Thanks for all the help so far.
So with a couple of shielding plates and the screened DC I am in a lot better place. No advance on the V4 buzz though, but hey.. it's the background hum I want to reduce. I will TRY and screen the AC heater cables today and see if that helps.
I have also noticed the 12BH7A valve is very hot, and only 540V not 640V as per the circuit diagram on pins 1 and 6 - does this prompt any ideas!
Thanks for all the help so far.
So with a couple of shielding plates and the screened DC I am in a lot better place. No advance on the V4 buzz though, but hey.. it's the background hum I want to reduce. I will TRY and screen the AC heater cables today and see if that helps.
I have also noticed the 12BH7A valve is very hot, and only 540V not 640V as per the circuit diagram on pins 1 and 6 - does this prompt any ideas!
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