radios hum

[micky]

I have several simple table radios, all transistor, made between the
70's and 80's, and 2 or 3 of them hum, even when they are turned off.
The humming is coming out of the speaker. How can that be?

In each case, the on/off switch must be working, because when I turn it
on, a radio program comes out. When I t turn it off, only the hum. In
one case, I put a separate switch on the wire to the speaker, and now
the radio makes no noise when it's off.

[gghe...@gmail.com]

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

George H.

[mog...@hotmail.com]

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.

[Smarty]

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

[RobertMacy]

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?

[John Robertson]

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 :-#)#
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[Allodoxaphobia]

On Wed, 18 Feb 2015 10:45:31 -0500, Smarty wrote:

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

heh...

s/know/understand/

[Dave Platt]

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)?

[Jon Elson]

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

[Allodoxaphobia]

On Wed, 18 Feb 2015 11:28:07 -0800, Dave Platt wrote:
>
> 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?

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

> Model number(s)?

Yes, please!

[mog...@hotmail.com]

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)

[Mike]

On Thu, 19 Feb 2015 09:15:21 -0800, mogulah wrote:

> (Why keep going back further and further into time)

I take it you are not getting older?

Mike.

[captainvi...@gmail.com]

On Wednesday, February 18, 2015 at 6:36:28 AM UTC-5, micky wrote:

some of us appreciate time travel. Lenny

[amdx]

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

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[amdx]

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

[mog...@hotmail.com]

On Monday, February 23, 2015 at 12:50:32 PM UTC-5, amdx wrote:
> On 2/18/2015 5:36 AM, micky wrote:
> > I have several simple table radios, all transistor, made between the
> > 70's and 80's, and 2 or 3 of them hum, even when they are turned off.
> > The humming is coming out of the speaker. How can that be?
> >
> > In each case, the on/off switch must be working, because when I turn it
> > on, a radio program comes out. When I t turn it off, only the hum.
> > In one case, I put a separate switch on the wire to the speaker, and now
> > the radio makes no noise when it's off.
>
> Do your lights also, put out just a little bit of light when
> you turn them off?

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

[mog...@hotmail.com]

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.

[amdx]

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

[mog...@hotmail.com]

On Tuesday, February 24, 2015 at 9:08:36 AM UTC-5, amdx wrote:
> On 2/18/2015 2:43 PM, Jon Elson wrote:
> > micky wrote:
> >
> >> I have several simple table radios, all transistor, made between the
> >> 70's and 80's, and 2 or 3 of them hum, even when they are turned off.
> >> The humming is coming out of the speaker. How can that be?
> >>
> >> In each case, the on/off switch must be working, because when I turn it
> >> on, a radio program comes out. When I t turn it off, only the hum. In
> >> one case, I put a separate switch on the wire to the speaker, and now
> >> the radio makes no noise when it's off.
>
>
> > 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.
>

> That's probably the best answer, although in the 70s,

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.

[amdx]

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?