{Collins} R390A audible hum

Hi All,Bill's remedy is rather good,if the transformer is potted and sealed,they are usually immersed in pitch/bitumin.
Over the years heat & gravity do their work and it  pools to the bottom of the casing.
placing the unit upside down in a WARM oven will allow the pitch/bitumin to recover the transformer top once more and this may stop the audible hum.
I put the warm unit in the 'fridge for a couple of hours before putting right side up.
Most important, ensure XYL is out shopping when you do this!
73 from VK4VN

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