The local small-town electrical utility supervisor contacted me
requesting assistance in locating a TV interference source. A homeowner,
experienceing severe TV problems and thinking the trouble was with his
set had purchased a new one and experienced the same troubles. The
utility crew recognized it as electrical interference but was not able
to pinpoint the source. Using a Sony AM/SW portable, I quickly found a
nearby pole supporting a large transformer that fed several houses. I
told the utility forman to start pulling the meter from each house
individually to see which one caused the noise to stop. When the third
meter was pulled, the noise ceased. Replacing it restored the noise.
Walking up to the door of the house, I pushed the doorbell button. The
noise stopped instantly. The house happened to be the one where the
owner had all the TV interference. I asked him where his doorbell
transformer was and he didn't know. The utility crew soon found it in
the attic-under 10 inches of blown-in insulation. It was a smelly,
tarry, overheated, arcing blob. Doorbell transformers seem to be cheaply
built and characteristically underrated and everyone I have seen in
service runs very hot. The primary stays powered up all the time and
the doorbell switch is in the secondary.(you don't want 120vac on dhe
doorbell switch) It should always be a prime suspect in residential
noise cases. I use a communications quality transformer as the doorbell
transformer in my house. It runs cool.
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