It hums even when it is turned off

markshan

Sir Thrift a Lot
I have an old Radio Shack table radio (solid state) and it has been in regular use for years. I've noticed lately that there is an audible hum (not loud, but noticeable) and a small vibration coming from the unit even when it is turned off. My wild guess is that perhaps the power switch is wired after the AC transformer, and the transformer is humming. If so, it's not really bothersome, but is it unsafe? TIA.
 
It seems that a solid state unit wouldn't have the power switch AFTER the transformer sine it would be "instant-on" without any need for standby filament voltage, but anything is possible. If the transformer is humming/buzzing, it probably bears looking into. It could be insulation breakdown from years of thermal and voltage stress. or loose core laminations, or a loose core in the case, or various other problems.
 
Most likely the power transformer is always connected to the AC line - power switched on the secondary side.
No worries if the set works as it should.
 
So the consensus seems to be that it isn't unsafe (I'll try reversing the plug later). In a related question, if the transformer is always hot, does that mean that the unit is consuming electricity, even when it is not on? Seems so, I guess the better question is if it is consuming an appreciable amount of electricity.
 
Does it have a digital clock? Digital radio? This would usually explain constant power but is no different than today's clocks and smart phone adaptors/wall warts.
 
When not in use, I would unplug it, not worth a fire that could endanger your family, especially a cheap tabletop radio. I would say find a replacement tranny for it if it is a sentimental piece, probably find a donor at most any fleamarket

So the consensus seems to be that it isn't unsafe (I'll try reversing the plug later). In a related question, if the transformer is always hot, does that mean that the unit is consuming electricity, even when it is not on? Seems so, I guess the better question is if it is consuming an appreciable amount of electricity.
 
Any heat that is produced is wasted energy, so yes, it does consume electricity if it has any sort of heat coming from it.
 
I have the same thing with a Toshiba XR-J9 CD player. Actually, it hums ONLY when the unit is off. When I turn it on, the hum goes away.
I'm guessing that they used a cheap power switch that is rated for lower voltage, which is why it is on the secondary side. There's no other reason on this CDP to do this that comes to mind.
 
Oh, and it apparently does cause strain and transformer failure eventually, I actually have two XR-J9s, the other has blown transformer. Obviously, I unplug the unit when I'm not using it.
 
Any heat that is produced is wasted energy, so yes, it does consume electricity if it has any sort of heat coming from it.

An "unloaded" transformer as used in these radios is quite small, about the size of a wall-wart tranny, and would draw at best a fraction of a watt - hardly anything to fuss over.
 
FWIW, some transformers in older equipment may not be in top form any more, and the accumulated thermal and voltage stress from years of operation coupled with the more recent challenge of all kinds of nasty, spiky line noise thrown out by all the switching power supplies connected to your system may manifest itself as mechanical noise, possibly a sign of imminent failure.
 
FWIW, some transformers in older equipment may not be in top form any more, and the accumulated thermal and voltage stress from years of operation coupled with the more recent challenge of all kinds of nasty, spiky line noise thrown out by all the switching power supplies connected to your system may manifest itself as mechanical noise, possibly a sign of imminent failure.

Be sure and let me know when the sky starts to fall down, ok?
 
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