Quote:
Originally Posted by Mazda Man
Once 're connected to the isolation TX the effect is all but gone.
Thanks
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If this is the case, that the hum bar you are seeing is gone when the isolation TX is fitted, this suggests there is a 50Hz current flowing in the RF connection to the set and modulating the signal. The problem cannot be residing inside the set, with issues of poor HT filtering, or heater to cathode leakage, or the effect will still be there with the set running from the isolation transformer. It sounds therefore like a classic earth loop or in this case neutral loop issue.
I don't know your set but I assume its a hot chassis type or you would not have deployed the isolation transformer in the first instance.
So I could suggest firstly check, when its running without the isolation tranny, that the chassis is connected to mains neutral and not phase and then if the problem is still there place a 470pF capacitor in series with both the RF connections to the set (the coax earth and the signal feed) to reduce any 50Hz currents in the RF feed.