I just got this radio and it seemed to play fine. However after it is on a short while, I loose the sound on the broadcast channels from 600kc to about 770. As I move up the band they go one at at time up to 800kc. The remaining channels play well from 800kc on. After a while, the channels that I lost initially come back.

Where the BC channels are lost, there is some hum from the filters, but no sound.

The same thing happens on SW, it plays well on start up and quickly dies, with no sound on any SW channel, but I still get some normal filter hum. The SW band never comes back unless I shut the radio off and turn it on again. It then plays well for a while and dies out in a few minutes again.

Does anyone know what may cause this? I am not sure where to start.

Thanks.

Hi Steve,

That is indeed a weird problem. The more weird it is, the fewer causes are possible.
I think the only thng that can cause that is a problem in the tuning condenser. I think a leaf of it must be just barely touching when warmed to a particular temperature.
The bearings at one end may be bad and causing this.

Best Regards,

Bill Grimm

Thanks. The chassis is very clean, the tuning cap is clean and has no binding. It does not get warm (to touch) that I can tell.

I can shut the radio off through the volune switch and immediately turn it on and the sound returns. After about 30 seconds, it is gone again.

:Hi Steve,
:
: That is indeed a weird problem. The more weird it is, the fewer causes are possible.
: I think the only thng that can cause that is a problem in the tuning condenser. I think a leaf of it must be just barely touching when warmed to a particular temperature.
: The bearings at one end may be bad and causing this.
:
:Best Regards,
:
:Bill Grimm

Have you substituted any of the tubes? In particular the 1L6? You can use a 1R5 in it's place though it won't work well in the higher SW bands as a good 1L6. Just a thought.

:I just got this radio and it seemed to play fine. However after it is on a short while, I loose the sound on the broadcast channels from 600kc to about 770. As I move up the band they go one at at time up to 800kc. The remaining channels play well from 800kc on. After a while, the channels that I lost initially come back.
:
:Where the BC channels are lost, there is some hum from the filters, but no sound.
:
:The same thing happens on SW, it plays well on start up and quickly dies, with no sound on any SW channel, but I still get some normal filter hum. The SW band never comes back unless I shut the radio off and turn it on again. It then plays well for a while and dies out in a few minutes again.
:
:Does anyone know what may cause this? I am not sure where to start.
:
:Thanks.

No I haven't tried the tube. I do not have one. I should be able to get one tomorrow at a local club. I can try it, but I don't see how the tube would be so selective and only block out SW and the lower AM band so soon after the radio is turned on. I am new to this.
Thanks for your help.

:Have you substituted any of the tubes? In particular the 1L6? You can use a 1R5 in it's place though it won't work well in the higher SW bands as a good 1L6. Just a thought.
:
::I just got this radio and it seemed to play fine. However after it is on a short while, I loose the sound on the broadcast channels from 600kc to about 770. As I move up the band they go one at at time up to 800kc. The remaining channels play well from 800kc on. After a while, the channels that I lost initially come back.
::
::Where the BC channels are lost, there is some hum from the filters, but no sound.
::
::The same thing happens on SW, it plays well on start up and quickly dies, with no sound on any SW chan.nel, but I still get some normal filter hum. The SW band never comes back unless I shut the radio off and turn it on again. It then plays well for a while and.dies out in a few minutes again.
::
::Does anyone know what may cause this? I am not sure where to start.
::
::Thanks.

Good question. In trouble shooting seems best to try the obvious/easiest first. Since trying known good tubes doesn't involve removing the chassis, seems like a good place to start... or at least to assure yourself it's not the pesky 1L6 acting up. BTW don't remove tubes while the radio is powered on – you'll blow filaments.

If the tubes check out OK, the next place I'd look would be the band switch tower. The contacts may need cleaning. Since everything passes through the BC contacts, the SW band would be affected as you said it is.

Failing that, you'll need to pull the chassis and do some systematic trouble shooting.

:Good question. In trouble shooting seems best to try the obvious/easiest first. Since trying known good tubes doesn't involve removing the chassis, seems like a good place to start... or at least to assure yourself it's not the pesky 1L6 acting up. BTW don't remove tubes while the radio is powered on – you'll blow filaments.
:
:If the tubes check out OK, the next place I'd look would be the band switch tower. The contacts may need cleaning. Since everything passes through the BC contacts, the SW band would be affected as you said it is.
:
:Failing that, you'll need to pull the chassis and do some systematic trouble shooting.

SteveB: When you clean the band switches be very careful to not break any of the fine wires on the coils. A can of compressed air helps get the heavy dust out, and a pipe cleaner soaked with contact cleaner works very well and helps "scrub" the contacts a bit. I would avoid using spray contact cleaner since it gets on things where it shouldn't be.
I'm not sure this is the cause of the problem you're experiencing, but a good cleaning of the band switches is always recommended.
Steve

::Good question. In trouble shooting seems best to try the obvious/easiest first. Since trying known good tubes doesn't involve removing the chassis, seems like a good place to start... or at least to assure yourself it's not the pesky 1L6 acting up. BTW don't remove tubes while the radio is powered on – you'll blow filaments.
::
::If the tubes check out OK, the next place I'd look would be the band switch tower. The contacts may need cleaning. Since everything passes through the BC contacts, the SW band would be affected as you said it is.
::
::Failing that, you'll need to pull the chassis and do some systematic trouble shooting.
:
:SteveB: When you clean the band switches be very careful to not break any of the fine wires on the coils. A can of compressed air helps get the heavy dust out, and a pipe cleaner soaked with contact cleaner works very well and helps "scrub" the contacts a bit. I would avoid using spray contact cleaner since it gets on things where it shouldn't be.
:I'm not sure this is the cause of the problem you're experiencing, but a good cleaning of the band switches is always recommended.
:Steve

Thanks. I did remove the chassis tonight. I do not have any extra tubes right now, but did spray the bandswitches, clean up everything that I could and then checked voltages.

The voltages are: on the IU4 (RF AMP)=84, should be 80; IL6=83, should be 96; 1U4 (IF amp)=82, should be 94; IU5 is 26, should be 25; and 3V4=82, should be 94.

I looked at the rectifier and it was 90v where it should read 105v at the 50A1. The drop on the rectifier itself was 99 (the schematic doesn't say what it should be) and the drop on the resistor after it is 9v. My household voltage is 117v. I wonder if the rectifier is low powered and that is the problem? It does warm up and the output may change from cold. I'll have to try the tube voltages again when it is cold (i tried checking again after about an hour, but the voltages were the same).

:Does anyone know what may cause this? I am not sure where to start.
:
:Thanks.

It is pretty much a waste of time to troubleshoot for a problem until the radio has been restored. Replace the filters, the paper capacitors and check the resistors. Clean the bandswitch and controls. This should solve your problems.

Dave

::Does anyone know what may cause this? I am not sure where to start.
::
::Thanks.
:
:It is pretty much a waste of time to troubleshoot for a problem until the radio has been restored. Replace the filters, the paper capacitors and check the resistors. Clean the bandswitch and controls. This should solve your problems.
:
:Dave

I agree. I did change the rectifier out with a diode and dropping resitor. The problem was solved. Aparently loosing channels is common symptyom of a bad rectifier.

I will recap and clean bandswitches now to avoid any other unforseen problems.

:::Does anyone know what may cause this? I am not sure where to start.
:::
:::Thanks.
::
::It is pretty much a waste of time to troubleshoot for a problem until the radio has been restored. Replace the filters, the paper capacitors and check the resistors. Clean the bandswitch and controls. This should solve your problems.
::
::Dave
:
:I agree. I did change the rectifier out with a diode and dropping resitor. The problem was solved. Aparently loosing channels is common symptyom of a bad rectifier.
:
:I will recap and clean bandswitches now to avoid any other unforseen problems.

My guess would be that the low rectifier voltage was making the local oscillator quit at the low end of the band.
Lewis

::::Does anyone know what may cause this? I am not sure where to start.
::::
::::Thanks.
:::
:::It is pretty much a waste of time to troubleshoot for a problem until the radio has been restored. Replace the filters, the paper capacitors and check the resistors. Clean the bandswitch and controls. This should solve your problems.
:::
:::Dave
::
::I agree. I did change the rectifier out with a diode and dropping resitor. The problem was solved. Aparently loosing channels is common symptyom of a bad rectifier.
::
::I will recap and clean bandswitches now to avoid any other unforseen problems.
:
:
:My guess would be that the low rectifier voltage was making the local oscillator quit at the low end of the band.
:Lewis

:::Does anyone know what may cause this? I am not sure where to start.
:::
:::Thanks.
::
::It is pretty much a waste of time to troubleshoot for a problem until the radio has been restored. Replace the filters, the paper capacitors and check the resistors. Clean the bandswitch and controls. This should solve your problems.

I really don't think you solved the problem. The filter capacitors are leaky drawing the B+ down, or you may have othe capacitors leaky which draws it down. Replacing the selenium with a diode just forces more current through the leaky filters and brings up the B+ and filament voltage. When the filters finally blow and short the diode the tube filaments will be history also. Its your choice, fix it now or fix a lot more later. I have never seen a bad selenium in a TO, I have seen lots of leaky capacitors.

Dave
::
::Dave
:
:I agree. I did change the rectifier out with a diode and dropping resitor. The problem was solved. Aparently loosing channels is common symptyom of a bad rectifier.
:
:I will recap and clean bandswitches now to avoid any other unforseen problems.