I have a 1942 Zenith model 6D525, it is little table model with 6 tubes. It also happens to be the model with the old rubber wiring. I have completely rebuilt this set all new wiring, resistors, and caps. It works great and is a very sensitive little receiver.

However, I have one problem. Whenever I tune below 650KHz, or specifically between 540KHz and 650KHz, I get a horrible buzz like the power supply is not being properly filtered. There are a couple of strong stations in that range and I can hear them under the very loud buzzing.

I have tested all the tubes, they all test OK. I replaced the tubes one by one with other tubes I had to see if a tube might be bad even though it tested good, no luck. I tried increasing the value of the AVC bypass capacitor, still no luck. The electrolytics are 20uF units, but that would not be the problem because once I tune above 650KHz, the radio works clear and loud with no buzz at all.

Does anyone have any suggestions as to where this may be coming from? Any ideas would be appreciated.

Dave

:I have a 1942 Zenith model 6D525, it is little table model with 6 tubes. It also happens to be the model with the old rubber wiring. I have completely rebuilt this set all new wiring, resistors, and caps. It works great and is a very sensitive little receiver.
:
:However, I have one problem. Whenever I tune below 650KHz, or specifically between 540KHz and 650KHz, I get a horrible buzz like the power supply is not being properly filtered. There are a couple of strong stations in that range and I can hear them under the very loud buzzing.
:
:I have tested all the tubes, they all test OK. I replaced the tubes one by one with other tubes I had to see if a tube might be bad even though it tested good, no luck. I tried increasing the value of the AVC bypass capacitor, still no luck. The electrolytics are 20uF units, but that would not be the problem because once I tune above 650KHz, the radio works clear and loud with no buzz at all.
:
:Does anyone have any suggestions as to where this may be coming from? Any ideas would be appreciated.
:
:Dave

Dave R,

The buzz may be coming from something in your house such as light dimmers, wireless devices, computers, VCR/DVD player, etc. If you have a portable radio with AM, try tuning in the same place on the dial on it and see if you pick up the buzz. There are lots of things that cause interference.

Radiodoc

::I have a 1942 Zenith model 6D525, it is little table model with 6 tubes. It also happens to be the model with the old rubber wiring. I have completely rebuilt this set all new wiring, resistors, and caps. It works great and is a very sensitive little receiver.
::
::However, I have one problem. Whenever I tune below 650KHz, or specifically between 540KHz and 650KHz, I get a horrible buzz like the power supply is not being properly filtered. There are a couple of strong stations in that range and I can hear them under the very loud buzzing.
::
::I have tested all the tubes, they all test OK. I replaced the tubes one by one with other tubes I had to see if a tube might be bad even though it tested good, no luck. I tried increasing the value of the AVC bypass capacitor, still no luck. The electrolytics are 20uF units, but that would not be the problem because once I tune above 650KHz, the radio works clear and loud with no buzz at all.
::
::Does anyone have any suggestions as to where this may be coming from? Any ideas would be appreciated.
::
::Dave
:
:Dave R,
:
:The buzz may be coming from something in your house such as light dimmers, wireless devices, computers, VCR/DVD player, etc. If you have a portable radio with AM, try tuning in the same place on the dial on it and see if you pick up the buzz. There are lots of things that cause interference.
:
:Radiodoc
:
Hey Doc,

If I tune another radio to the same frequency, sitting right next to my Zenith, it does not buzz. I have even taken my Zenith to the basement, other rooms and even tried upstairs, but every time I get the hum. I'll keep looking!

Thanks...... David R

:::I have a 1942 Zenith model 6D525, it is little table model with 6 tubes. It also happens to be the model with the old rubber wiring. I have completely rebuilt this set all new wiring, resistors, and caps. It works great and is a very sensitive little receiver.
:::
:::However, I have one problem. Whenever I tune below 650KHz, or specifically between 540KHz and 650KHz, I get a horrible buzz like the power supply is not being properly filtered. There are a couple of strong stations in that range and I can hear them under the very loud buzzing.
:::
:::I have tested all the tubes, they all test OK. I replaced the tubes one by one with other tubes I had to see if a tube might be bad even though it tested good, no luck. I tried increasing the value of the AVC bypass capacitor, still no luck. The electrolytics are 20uF units, but that would not be the problem because once I tune above 650KHz, the radio works clear and loud with no buzz at all.
:::
:::Does anyone have any suggestions as to where this may be coming from? Any ideas would be appreciated.
:::
:::Dave
::
::Dave R,
::
::The buzz may be coming from something in your house such as light dimmers, wireless devices, computers, VCR/DVD player, etc. If you have a portable radio with AM, try tuning in the same place on the dial on it and see if you pick up the buzz. There are lots of things that cause interference.
::
::Radiodoc
::
:Hey Doc,
:
:If I tune another radio to the same frequency, sitting right next to my Zenith, it does not buzz. I have even taken my Zenith to the basement, other rooms and even tried upstairs, but every time I get the hum. I'll keep looking!
:
:Thanks...... David R

Connecting an alligator jumper clip across the loop antenna would kill the RF stage and pretty definitely tell if the interference is coming from the inside or outside world. If you connect a long piece of wire to the antenna terminal and run it outside, away from the house and power lines, how does the station that is in the interference act? Is the radio sitting right next to the Zenith a AC or battery? If it is a transistor, you could have something coming from the AC mains. Try those ideas, and I will be thinking of something else.

Lewis