Old Audio Receiver Hum?

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Recently inherited an old Scott AM/FM Receiver model 319RA (no tubes)
that had been stored for a very long time.

Checked all the fuses and none were blown so turned it on and heard
loud power supply hum using headphones over the entire Volume Control
range (even when set to minimum).

Appreciate any suggestions and tips from someone who has had experience
restoring old audio amps and receivers.

Thanks

Gene

 

[harrogate2]

Recently inherited an old Scott AM/FM Receiver model 319RA (no tubes)
that had been stored for a very long time.

Checked all the fuses and none were blown so turned it on and heard
loud power supply hum using headphones over the entire Volume Control
range (even when set to minimum).

Appreciate any suggestions and tips from someone who has had experience
restoring old audio amps and receivers.

Thanks

Gene

The power supply smoothing capacitor will have dried out. Replace it
with a similar value and all will be well. You hear the hum all the
time as it is the signal input to the power amp that is varied by the
volume control, not the output of the amp itself.

The other point is that you will hear a lot of noise and hum if the
headphone connection is directly across the loudspeaker (in effect)
with no padding. Put a resistor of 220R-330R in series with the
headphones (each channel if stereo) and the noise will disappear as if
by magic.

 

[john]

Sounds like the main filter cap has dried up, look at the
power supply you should see a large electrolytic filter cap.
Change that with a new one that should fix you up.
Failing that check all the filter caps.

kip

 

[Bradley1234]

What test tools do you have?? DVM, soldering iron, scope, etc?

Safety training? there are usually unsafe 120vAC points in older equipment.
The household power is dangerous because at 60 cycles/second if you get a
shock it will try to make your heart go at 60/second instead of about 60 per
minute. The individual heart muscles will fibrilate in different
directions, out of sync, many times unable to recover.

Every house should own a defibrillator device, they are cheap these days

 

[harrogate2]

What test tools do you have?? DVM, soldering iron, scope, etc?

Safety training? there are usually unsafe 120vAC points in older equipment.
The household power is dangerous because at 60 cycles/second if you get a
shock it will try to make your heart go at 60/second instead of about 60 per
minute. The individual heart muscles will fibrilate in different
directions, out of sync, many times unable to recover.

Every house should own a defibrillator device, they are cheap these days

What a load of crap!

The danger from electricity is NOTHING to do with supply frequency -
it is all about current. A current of 30mA - that is 0.03A - passing
through your body across your heart will usually be fatal. 10mA may
cause problems, but in a healthy person will usually not be fatal.

120V (to earth) as used in the US is specifically chosen since it is
rarely high enough to cause 30mA current flow through the body: by the
same token here in the UK and across most of Europe, 110V (actually
55-0-55) is used professionally for power tools etc.

However our normal mains is 220V in Europe, 240V in the UK (that is to
earth) and can be fatal. I understand that in the US 240V is available
across both supply lines but it is actually 120-0-120 and thus much
less dangerous.

 

[Bradley1234]

What a load of crap!

The danger from electricity is NOTHING to do with supply frequency -
it is all about current. A current of 30mA - that is 0.03A - passing
through your body across your heart will usually be fatal. 10mA may
cause problems, but in a healthy person will usually not be fatal.

120V (to earth) as used in the US is specifically chosen since it is
rarely high enough to cause 30mA current flow through the body: by the
same token here in the UK and across most of Europe, 110V (actually
55-0-55) is used professionally for power tools etc.

The number of people who believe that normal household current is not
lethal or that powerlines are insulated and do not pose a hazard is
alarming. Electrocutions may result from contact with an object as seemingly
innocuous as a broken light bulb or as lethal as an overhead powerline, and
have affected workers since the first electrical fatality was recorded in
France in 1879 when a stage carpenter was killed by an alternating current
of 250 volts. 2

However our normal mains is 220V in Europe, 240V in the UK (that is to
earth) and can be fatal. I understand that in the US 240V is available
across both supply lines but it is actually 120-0-120 and thus much
less dangerous.

My my, you seem to be very educated in this subject if what I said was a
load of (incorrect information.) Can you explain what happens to the heart
to make it stop? Why doesnt a defibrillator, which probably jolts more than
30mA, cause a person to die?

It would be proper for me to quote sources, rather than assume;
When current greater than the 16 mA "let go current" passes through the
forearm, it stimulates involuntary contraction of both flexor and extensor
muscles. When the stronger flexors dominate, victims may be unable to
release the energized object they have grasped as long as the current flows.
If current exceeding 20 mA continues to pass through the chest for an
extended time, death could occur from respiratory paralysis. Currents of 100
mA or more, up to 2 Amps, may cause ventricular fibrillation, probably the
most common cause of death from electric shock. 11 Ventricular
fibrillation is the uneven pumping of the heart due to the uncoordinated,
asynchronous contraction of the ventricular muscle fibers of the heart that
leads quickly to death from lack of oxygen to the brain. Ventricular
fibrillation is terminated by the use of a defibrillator, which provides a
pulse shock to the chest to restore the heart rhythm.

11. Dalziel CF, Lee WR [1968]. Re-evaluation of Lethal Electric Currents.
IEEE Trans. Ind. Gen. Appl. IGA-4:467-476.

http://www.cdc.gov/niosh/pdfs/98-131.pdf

 

[NSM]

| The number of people who believe that normal household current is not
| lethal or that powerlines are insulated and do not pose a hazard is
| alarming. Electrocutions may result from contact with an object as
seemingly
| innocuous as a broken light bulb or as lethal as an overhead powerline,
and
| have affected workers since the first electrical fatality was recorded in
| France in 1879 when a stage carpenter was killed by an alternating current
| of 250 volts.

I heard of 80 VDC from an aircraft starter killing one guy under normal
(non-hospital) conditions.

N

 

[WEBPA]

Capacitors. Replace 'em.

Recently inherited an old Scott AM/FM Receiver model 319RA (no tubes)
that had been stored for a very long time.

Checked all the fuses and none were blown so turned it on and heard
loud power supply hum using headphones over the entire Volume Control
range (even when set to minimum).

Appreciate any suggestions and tips from someone who has had experience
restoring old audio amps and receivers.

Thanks

Gene

webpa

 

[Pcaorwb]

With old equipment....go for straight for the Caps.

BobbyB
Tucson, AZ

 

[Scarm10]

Yeah Caps were the trick with mine. IDK if anyone else has any info about my scott319RA, but if you know anything I would really appreciate it. if you have like the year or something. and what does h.h. mean in h.h.Scott?