Hi, a co-worker found a Packard Bell 5DA in his fathers garage and asked me if I wanted to fix it so he could surprise his father. I eagerly accepted and restored the radio.
I use the AVC voltage to make all adjustments and noticed I was getting very little signal on my digital meter (max about -.9 VDC) however the radio received many stations clear and the dial was spot on so I brought the radio in and gave it back to my co-worker. I had replaced all components including mica’s and resistors as I did not want the radio to have problems later.

His father took it to work (down town Los Angeles) where he plays it in his office and noticed in the wee early morning hours the station that he listens to came in clear however when traffic picks up and trucks start rolling in the radio becomes statically and the static overrides the radio station. I asked to have the radio returned to me so I could check it out.

Not having a lot of experience with electronics or vintage radios I felt it had something to do with the AVC voltage being low and in that condition amplification would be high causing any static signals to pass right through to the audio section.
Inspecting my work I found R3 had a 5.1 Meg installed when the schematic called out a 2.2 Meg. I intended to parallel two 5.1 meg. but overlooked it.

The AVC signal came up to –6.0 volts on a strong signal alignment of the I.F.’s was more easy to set so the radio is back to the owner and I am waiting to see if this made a difference.

My questions as follows,

How do you determine what is normal AVC voltage per given radio?

Is my thinking a properly working AVC helps considerably in reducing interference or background noise.

Larry

I don't know if the AVC would cause that. I wonder if he is picking up the sideband distortion from an adjacent station broadcasting in HD radio. Some stations limit their HD hours of operation and it may be conicental when his issue begins.

http://www.am-dx.com/amiboc.htm

:Hi, a co-worker found a Packard Bell 5DA in his fathers garage and asked me if I wanted to fix it so he could surprise his father. I eagerly accepted and restored the radio.
:I use the AVC voltage to make all adjustments and noticed I was getting very little signal on my digital meter (max about -.9 VDC) however the radio received many stations clear and the dial was spot on so I brought the radio in and gave it back to my co-worker. I had replaced all components including mica’s and resistors as I did not want the radio to have problems later.
:
:His father took it to work (down town Los Angeles) where he plays it in his office and noticed in the wee early morning hours the station that he listens to came in clear however when traffic picks up and trucks start rolling in the radio becomes statically and the static overrides the radio station. I asked to have the radio returned to me so I could check it out.
:
:Not having a lot of experience with electronics or vintage radios I felt it had something to do with the AVC voltage being low and in that condition amplification would be high causing any static signals to pass right through to the audio section.
:Inspecting my work I found R3 had a 5.1 Meg installed when the schematic called out a 2.2 Meg. I intended to parallel two 5.1 meg. but overlooked it.
:
:The AVC signal came up to –6.0 volts on a strong signal alignment of the I.F.’s was more easy to set so the radio is back to the owner and I am waiting to see if this made a difference.
:
:My questions as follows,
:
:How do you determine what is normal AVC voltage per given radio?
:
:Is my thinking a properly working AVC helps considerably in reducing interference or background noise.
:
:Larry
:
:

Hi Larry

AM radio will receive electrical interference.

AVC becomes more negative on stronger stations. Minus 6 volts may be reasonable on a specific radio. Depending on alignment, distance to station, antenna AVC readings will vary.

AVC will reduce signal strength on strong stations. It tries to equalize volume between local and distance stations. The only way it reduces interference is by limiting volume on stronger stations.

Shorting out AVC will cause increased volume. In some cases AVC can be shorted and a person operating a radio wouldn't know the difference. Too strong of a signal will cause distortion without AVC.

Norm

:I don't know if the AVC would cause that. I wonder if he is picking up the sideband distortion from an adjacent station broadcasting in HD radio. Some stations limit their HD hours of operation and it may be conicental when his issue begins.
:
:http://www.am-dx.com/amiboc.htm
:
::Hi, a co-worker found a Packard Bell 5DA in his fathers garage and asked me if I wanted to fix it so he could surprise his father. I eagerly accepted and restored the radio.
::I use the AVC voltage to make all adjustments and noticed I was getting very little signal on my digital meter (max about -.9 VDC) however the radio received many stations clear and the dial was spot on so I brought the radio in and gave it back to my co-worker. I had replaced all components including mica’s and resistors as I did not want the radio to have problems later.
::
::His father took it to work (down town Los Angeles) where he plays it in his office and noticed in the wee early morning hours the station that he listens to came in clear however when traffic picks up and trucks start rolling in the radio becomes statically and the static overrides the radio station. I asked to have the radio returned to me so I could check it out.
::
::Not having a lot of experience with electronics or vintage radios I felt it had something to do with the AVC voltage being low and in that condition amplification would be high causing any static signals to pass right through to the audio section.
::Inspecting my work I found R3 had a 5.1 Meg installed when the schematic called out a 2.2 Meg. I intended to parallel two 5.1 meg. but overlooked it.
::
::The AVC signal came up to –6.0 volts on a strong signal alignment of the I.F.’s was more easy to set so the radio is back to the owner and I am waiting to see if this made a difference.
::
::My questions as follows,
::
::How do you determine what is normal AVC voltage per given radio?
::
::Is my thinking a properly working AVC helps considerably in reducing interference or background noise.
::
::Larry
::
::
:

Are there any large motors near or in is his building?
I work at a Baseball Batting cage(I fixed a few radios at work :) and every time a motor would start the radio would have very loud static untill the motor reached full rpm's. Construction work may also cause some static for the same reason the Batting cages do, motors.
Ian

:Hi Larry
:
: AM radio will receive electrical interference.
:
: AVC becomes more negative on stronger stations. Minus 6 volts may be reasonable on a specific radio. Depending on alignment, distance to station, antenna AVC readings will vary.
:
: AVC will reduce signal strength on strong stations. It tries to equalize volume between local and distance stations. The only way it reduces interference is by limiting volume on stronger stations.
:
: Shorting out AVC will cause increased volume. In some cases AVC can be shorted and a person operating a radio wouldn't know the difference. Too strong of a signal will cause distortion without AVC.
:
:Norm
:
:
::I don't know if the AVC would cause that. I wonder if he is picking up the sideband distortion from an adjacent station broadcasting in HD radio. Some stations limit their HD hours of operation and it may be conicental when his issue begins.
::
::http://www.am-dx.com/amiboc.htm
::
:::Hi, a co-worker found a Packard Bell 5DA in his fathers garage and asked me if I wanted to fix it so he could surprise his father. I eagerly accepted and restored the radio.
:::I use the AVC voltage to make all adjustments and noticed I was getting very little signal on my digital meter (max about -.9 VDC) however the radio received many stations clear and the dial was spot on so I brought the radio in and gave it back to my co-worker. I had replaced all components including mica’s and resistors as I did not want the radio to have problems later.
:::
:::His father took it to work (down town Los Angeles) where he plays it in his office and noticed in the wee early morning hours the station that he listens to came in clear however when traffic picks up and trucks start rolling in the radio becomes statically and the static overrides the radio station. I asked to have the radio returned to me so I could check it out.
:::
:::Not having a lot of experience with electronics or vintage radios I felt it had something to do with the AVC voltage being low and in that condition amplification would be high causing any static signals to pass right through to the audio section.
:::Inspecting my work I found R3 had a 5.1 Meg installed when the schematic called out a 2.2 Meg. I intended to parallel two 5.1 meg. but overlooked it.
:::
:::The AVC signal came up to –6.0 volts on a strong signal alignment of the I.F.’s was more easy to set so the radio is back to the owner and I am waiting to see if this made a difference.
:::
:::My questions as follows,
:::
:::How do you determine what is normal AVC voltage per given radio?
:::
:::Is my thinking a properly working AVC helps considerably in reducing interference or background noise.
:::
:::Larry
:::
:::
::
:

I think the AVC don't know if it's static or radio station. I see by the print the radio has a loop antenna, with an optional connection for more antenna. Could try 180 the plug in the wall. Or try an EMI filter too. Also try connecting a wire to the antenna connection, make a few turns around its own line cord. For a lose coupling antenna.