radios hum

Look at the power supply. Maybe old caps or something.

George H.

Hum is actually vibration. If there is a "14 AWG" or "12 AWG" wire behind the wall socket powering your radio, then you should change it to a "10 AWG" white colored wire.

A bigger wire can stop vibration easier for small electronics.

Most of these older radios hum when trying to play modern music. They hum because they don't know the words to the songs.

does location matter? Does hum last indefinitely, or just the time for all the caps to power down?

Do you have an LED light bulb, or CFI light bulb on the same circuit? Their 30KHz ballast likes to 'blast' back up into other stuff, or radiate, too.

Do you have a strong cell tower/spread spectrum communication tower nearby? Or, power lines overhead?

Does the hum go away when you unplug the radio from the wall outlet?

Any large transformers nearby if it still hums when unplugged and any batteries removed? Induced AC...

John :-#)#

heh...

s/know/understand/

One possibility is that these radios have some sort of interference-suppression or anti-kickback ("anti-pop") capacitor bridged across the on/off switch. This capacitor would allow a small amount of current to flow "around" the switch contacts when the switch is "off". If the cap is becoming "leaky" with age there might be enough current flowing to partially power up the radio even with the switch in the "off" position.

Another possibility is that it's mechanical hum rather than electrical. If the on/off switch is in the secondary (low-voltage) part of the power supply circuit, then there would be mains voltage present on the primary transformer windings at all times. The transformer could then be humming a bit, from magnetostriction, and the speaker cone could convert this mechanical vibration to audible noise. [This wouldn't account for your saying that adding a switch in the speaker wiring got rid of the hum, though.]

Do these radios have any sort of clock or light or ??? which would need power at all times, even when the radio is turned off?

Model number(s)?

A number of these radios will have 60 Hz (mains-powered) transformers that are always on. The power switch switches low-voltage (either AC or DC) power to turn the radio on or off. probably there is magnetic leakage from the transformer that is getting into the speaker or wiring somehow. If the audio output stage has an audio transformer to drive the speaker, the power transformer might be coupling magnetically to the audio output transformer. Possibly, altering the way the power transformer is mounted might reduce this coupling.

Jon

Or do they use remote control for volume, tune, etc. If so,they are always "on" (somewhat) -- even when they are off.

Yes, please!

No. This is too cavemanish. Junk the 70's transistor radios and get radio service and large speakers through a touch screen phone provider.

(Why keep going back further and further into time)

I take it you are not getting older?

Mike.

some of us appreciate time travel. Lenny

Is this more of your voodoo electronics? I don't think your joking with your reply. After trying to educate you on a simple concept and failing, ( I think I failed, never was sure you weren't pulling my leg the whole time)

Mikek

Do your lights also, put out just a little bit of light when you turn them off? Mikek

Hey Mr. Professor, why dont cha go over there, get a stun gun, fire it at the light bulb and find out.

If you want more voodoo crap, you can take the 14 or 12 wire's neutral and do an isolated ground. Might be as simple as just sending it to another transformer.

That's probably the best answer, although in the 70s, I'm not sure how many radios were always on. That throws in a little wrinkle. > "A number of these radios will have 60 Hz (mains-powered) transformers > that are always on."

Mikek

There is no "best answer". Humming could be caused by having too small of a path back (hence: my two answers as a solution). Humming could also be caused by something else running whether connected to your service or not.

Ok, please expound on how a small path back, ( I have to assume you mean a small gauge wire) will cause hum. You might also define why the color is important.

Humming could also be caused by something else running whether connected to your service or not.

Well that would depend on the definition of hum. I would think a common definition is a 120hz frequency emanating from the speaker often power supply related.. Although 60 hz also possible with other sources.

What's your definition?

Mikek