Weird hum in 41-280 - Printable Version
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Weird hum in 41-280 - Raleigh - 02-14-2008
Last summer I recapped and rewired a 41-280, and it has worked well ever since. I've listened to it a few times a week, often several hours at a time.
I had never noticed any hum, but a couple of days ago, I turned it on and heard the broadcast OK, but underneath there was a noticeable 120 Hz hum. The volume control had no effect. The hum was just as loud with the volume turned all the way down as when it was up.
After a few minutes I turned off the radio, waited five or ten seconds, turned it back on again, and there was no hum at all. I have listened to it almost daily since then and there is still no hum. If I turn the volume all the way down and put my ear next to the speaker, there is no audible hum at all.
Anybody have a theory about what could cause an intermittent hum of this sort?
- Ron Ramirez - 02-14-2008
First thing that comes to mind, beside intermittent H-K leakage/shorts in a tube, would be the Candohm B-C resistor (61). Bad loctal tube socket contacts could also be a culprit?
- Texasrocker - 02-21-2008
I agree with Ron!! Most likely, if the candohm hasnt been replaced, it is "trouble" waiting to happen!! Those rascals are T-r-o-u-b-l-e!!! Worst invention ever conceived IMOP!! Other sources of "intermittent 120 cycle hum", can be from modern in-home appliances such as clothes dryers, washing machines (spin cycle), other inhome modern appliances such as TVs sets, microwave ovens , etc. All play "havoc" on vintage tube radio reception!! The new style small "florescent tubular coil type light bulbs" that save-energy in our homes produce a "not so friendly" audio into vintage tube radios!! A good way to "isolate" AC interference ( if that is the prob?), .. is by connecting the vintage tube receiver to a AC (power strip) via end AC plug connected to 2 (.1-600v) bypass caps with both ends (-)of the caps going to "earth ground"!! Sure eliminates " AC pole transformers line hash", but still wont compensate for a bad "candohm"!! Randal
