Working on a philco 42-380 big floor radio.
it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.

:Working on a philco 42-380 big floor radio.
:it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.

Les:
The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
Lewis
:

Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.

Clifton

::Working on a philco 42-380 big floor radio.
::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
:
:
:
:Les:
:The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
:Lewis
::
:
:

:Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.
:
:Clifton
:
:::Working on a philco 42-380 big floor radio.
:::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
::
::
::
::Les:
::The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
::Lewis
::Sometimes a station is strong enough to causea mod-
::ulation hum,I have the same problem, turns out to
::be the furnace hook-up. So I'll wait till spring!
:
:

:Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.
:
:Clifton
:
:::Working on a philco 42-380 big floor radio.
:::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
::
::
::
::Les:
::The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
::Lewis
::I have the same problem at home. Turns out to be the
::furnace hook-up. I'll wait till spring.
::
:
:

:Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.
:
:Clifton
:
:::Working on a philco 42-380 big floor radio.
:::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
::
::
::
::Les:
::The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
::Lewis
::I have the same problem at home. Turns out to be the
::furnace hook-up. I'll wait till spring.
::
:
:

::Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.
::
::Clifton
::
::::Working on a philco 42-380 big floor radio.
::::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
:::
:::
:::
:::Les:
:::The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
:::Lewis
:::I have the same problem at home. Turns out to be the furnace hook-up. I'll wait till spring.Raymond
::
::
::
::
:
:

::Sounds like there may be an IF stage going into oscillation. If all paper caps have not been replaced, may need to check/replace any bypass caps in RF/IF stages from B+ to chassis/ground and caps in the AVC circuit. Make sure pins on tubes and tube sockets are clean.
::
::Clifton
::
::::Working on a philco 42-380 big floor radio.
::::it receives now it when I tune it to the 640 am it starts humming and ratteling the speaker like crazy! when I tune it away from there, it works. that is, it picks up stations. Only when it goes to 640 area it soinds like feed back. what can I check for? I changes most of the caps.
:::
:::
:::
:::Les:
:::The first thing I would do is to take another radio, preferably a portable transistor set, and check your house for 640 kHz coming from a lamp dimmer, computer, or whatever. I have two lamps in my house that are turned on, off, and dimmed by touching the metal lamp base. They radiate quite a bit of 940 kHz whether the lamps are on or off. You might have to trip circuit breakers to find out which circuit is causing the trouble, provided it is not the radio. This is a problem outside of the radio, to my thinking.
:::Lewis
:::I have the same problem at home. Turns out to be the furnace hook-up. I'll wait till spring.Raymond
::
::
::
::
:
:

I had more of a squeal-howl in my Zenith 5-G-500 that would occur when I turned the dial to the extreme low end. I believe that it was feedback near the IF, and it only occurred when the loop was in the case. Readjustment of the IF transformers has eliminated this problem for the most part, so my guess is that for one reason or another the IF was adjusted a bit high.

Yours sounds more like it is picking up interference from some device in your home, however, whether a fundamental frequency or a harmonic. Many of the modern power supplies use high frequencies in order to significantly reduce the amount of iron and copper in the transformers, and these power supplies can radiate a lot of interference, even though the FCC rule part 15 supposedly does not allow for devices to cause interference with other devices. Wish they'd think of enforcing that for AM radio, because there are TONS of devices on the market today that absolutely destroy AM reception.

...or, like others have suggested, bad filter caps. Worth taking a peek. Best test in this case for electrolytics is a power factor test, which tests for series resistance. This is why the basic ohm meter test that so many of us have been taught to perform does not really tell much of anything about the condition of the capacitors, since it's very for a split second of meter deflection to determine much of anything about the capacitor in question other than that it has not dried up.
The Solar CB analyzer, for instance, not only looks for capacitance, but also looks for high voltage leakage (and arcing), and power factor (series resistance). It is able to measure internal series resistance by adding resistance at another balanced point on the bridge. Series resistance within the filter cap, due most likely to corrosion, makes it almost impossible for the capacitor to filter at higher frequencies, even if the capacitor can otherwise function at power supply frequencies.

:I had more of a squeal-howl in my Zenith 5-G-500 that would occur when I turned the dial to the extreme low end. I believe that it was feedback near the IF, and it only occurred when the loop was in the case. Readjustment of the IF transformers has eliminated this problem for the most part, so my guess is that for one reason or another the IF was adjusted a bit high.
:
:Yours sounds more like it is picking up interference from some device in your home, however, whether a fundamental frequency or a harmonic. Many of the modern power supplies use high frequencies in order to significantly reduce the amount of iron and copper in the transformers, and these power supplies can radiate a lot of interference, even though the FCC rule part 15 supposedly does not allow for devices to cause interference with other devices. Wish they'd think of enforcing that for AM radio, because there are TONS of devices on the market today that absolutely destroy AM reception.
:When you say tons, why do you treat them so nice? Like Tennesee Ernie Ford sang about 16 tons. He sang that song so man times there's more weight there than the world weighs. Ha. Raymond