Hudson Tube Car Radio

5/26/2013 10:06:44 AMLou

Guys:

I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.

One thing though.

I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?

Thanks
Lou

5/26/2013 10:26:23 AMLewis

Lou:
I have never been able to make a car radio work perfectly without being in a car. Izza matter of fact, every car has a different setting for the antenna trimmer. The car antenna seems to be a very high impedance (notice the co-axial lead in is not standard co-ax) Even using a a car antenna on a bench doesn't exactly work out because of the ground plane that isn't there. I wouldn't worry about the trimmer setting until the radio is in the car it is going to live in.
Lewis
:

5/26/2013 10:44:34 AMWarren

Agree with Lewis about the trimmer adjustment. When the radio is back in the car, the antenna fully extended. Adjust the trimmer for best performance.

5/26/2013 1:03:06 PMTom McHenry

It sounds like you don't have a procedure for setting the antenna trimmer. If I had to guess, based on how you described its effects on the radio, such a procedure would call for finding a station near the middle of the band (1100 KHz or thereabouts) and peaking the trimmer at that point. Assuming, of course, that a "flat" sensitivity is what is desirable (it may not be, if your locale tends to have all the stations clustered at one end of the dial or the other- that's the case in my AM listening area).

But in any event, the mere fact that twiddling the trimmer does affect how the radio performs is a good sign; final adjustment of it can obviously only be done when it is installed in its vehicle.

5/26/2013 9:53:02 PMeeprof

:Guys:
:
:I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
:
:One thing though.
:
:I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
:
:Thanks
:Lou
:Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.

5/26/2013 11:23:44 PMLou

:Thanks

PS : What if the generator you are using has a 50 ohm output? Do the series and shunt caps still apply?

Thanks
Lou

I may just leave this step until I get the radio into the car. It is working well and "I dont want to mess with it too much longer" because of its age.

Lou

:Guys:
::
::I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
::
::One thing though.
::
::I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
::
::Thanks
::Lou
::Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
:On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.
:
:

5/27/2013 9:04:11 AMeeprof

::Thanks
:
:PS : What if the generator you are using has a 50 ohm output? Do the series and shunt caps still apply?
:
:Thanks
:Lou
:
:I may just leave this step until I get the radio into the car. It is working well and "I dont want to mess with it too much longer" because of its age.
:
:Lou
:
::Guys:
:::
:::I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
:::
:::One thing though.
:::
:::I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
:::
:::Thanks
:::Lou
:::Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
::On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.

Lou: Yes, the dummy antenna caps still apply. Most RF generators have 50 ohm Z out. I still work on a good many tube auto radios so years ago I made up a motorola auto antenna plug with the caps in it so I could just plug it into the radio quickly when aligning. Tom
::
::
:
:

5/27/2013 10:45:47 AMLewis

:::Thanks
::
::PS : What if the generator you are using has a 50 ohm output? Do the series and shunt caps still apply?
::
::Thanks
::Lou
::
::I may just leave this step until I get the radio into the car. It is working well and "I dont want to mess with it too much longer" because of its age.
::
::Lou
::
:::Guys:
::::
::::I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
::::
::::One thing though.
::::
::::I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
::::
::::Thanks
::::Lou
::::Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
:::On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.
:
:Lou: Yes, the dummy antenna caps still apply. Most RF generators have 50 ohm Z out. I still work on a good many tube auto radios so years ago I made up a motorola auto antenna plug with the caps in it so I could just plug it into the radio quickly when aligning. Tom
:::

Lou:
May I say again:
Having the trimmer adjusted on the bench will NOT be the corrct adjustment for the car....co-ax length, antenna placement, ground plane,(car body) etc. are going to be different for every car. Adjust the antenna trimmer after the radio is in the car.
Lewis
:::
::
::
:
:

5/27/2013 2:44:33 PMLou

::::Thanks
:::
:::PS : What if the generator you are using has a 50 ohm output? Do the series and shunt caps still apply?
:::
:::Thanks
:::Lou
:::
:::I may just leave this step until I get the radio into the car. It is working well and "I dont want to mess with it too much longer" because of its age.
:::
:::Lou
:::
::::Guys:
:::::
:::::I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
:::::
:::::One thing though.
:::::
:::::I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
:::::
:::::Thanks
:::::Lou
:::::Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
::::On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.
::
::Lou: Yes, the dummy antenna caps still apply. Most RF generators have 50 ohm Z out. I still work on a good many tube auto radios so years ago I made up a motorola auto antenna plug with the caps in it so I could just plug it into the radio quickly when aligning. Tom
::::
:
:
:Lou:
:May I say again:
:Having the trimmer adjusted on the bench will NOT be the corrct adjustment for the car....co-ax length, antenna placement, ground plane,(car body) etc. are going to be different for every car. Adjust the antenna trimmer after the radio is in the car.
:Lewis

Thanks Lewis:

So I lined up the IF stages using 265 Kc with a modulated tone as the SAMS indicated. I then used on the air weak signals to tweak a few settings ( additional padder caps) AFTER the input RF stage, instead of using the generator and the matching circuit. I assume since the padders I tweaked were AFTER the first RF stage, then they would not be affected by the use or non - use of the input matching caps. The only trimmer affected would be the antenna trimmer which I will set in the car - true?

The radio now works very well, with good sensitivity across the AM band. The dial calibration is right on too.

Lou
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:::
:::
::
::
:
:

5/28/2013 8:29:08 PMeeprof

:::::Thanks
::::
::::PS : What if the generator you are using has a 50 ohm output? Do the series and shunt caps still apply?
::::
::::Thanks
::::Lou
::::
::::I may just leave this step until I get the radio into the car. It is working well and "I dont want to mess with it too much longer" because of its age.
::::
::::Lou
::::
:::::Guys:
::::::
::::::I have been working on an old, 1950s tube car radio. Got it all working after a recap, got the vibrator started ( it was stuck ) and it is working well.
::::::
::::::One thing though.
::::::
::::::I attached a long wire antenna to the antenna connection where you would normally attach a car radio antenna. When I turn out the antenna trimmer ( less capacitance ) the unit favors the lower end of the radio dial in terms of gain. When I turn the trimmer in ( more capacitance ) the unit favors the higher end of the band ( higher frequencies - more gain). Is this normal? Is it because I do not have the proper antenna attached with the proper loading?
::::::
::::::Thanks
::::::Lou
::::::Lou: The long wire antenna is a severe mismatch for the front end of that radio. The car's coax lead is actually part of the resonant circuit of the RF input.
:::::On the bench you must use a "dummy antenna" network to match the Z for alignment purposes. Your radio was probably made by Colonial and the dummy antenna consisted of two 39pf caps - one across the antenna input and the other in series with the input. That little "dummy" makes a WORLD difference.
:::
:::Lou: Yes, the dummy antenna caps still apply. Most RF generators have 50 ohm Z out. I still work on a good many tube auto radios so years ago I made up a motorola auto antenna plug with the caps in it so I could just plug it into the radio quickly when aligning. Tom
:::::
::
::
::Lou:
::May I say again:
::Having the trimmer adjusted on the bench will NOT be the corrct adjustment for the car....co-ax length, antenna placement, ground plane,(car body) etc. are going to be different for every car. Adjust the antenna trimmer after the radio is in the car.
::Lewis
:
:Thanks Lewis:
:
:So I lined up the IF stages using 265 Kc with a modulated tone as the SAMS indicated. I then used on the air weak signals to tweak a few settings ( additional padder caps) AFTER the input RF stage, instead of using the generator and the matching circuit. I assume since the padders I tweaked were AFTER the first RF stage, then they would not be affected by the use or non - use of the input matching caps. The only trimmer affected would be the antenna trimmer which I will set in the car - true?
:
:The radio now works very well, with good sensitivity across the AM band. The dial calibration is right on too.
:
:Lou
:::::
::::Lou: The I.F. alignment is fine to do as you described, however, that set has permeability tuning cores (iron slugs) in both the RF and Antenna tuning sections. You cannot correctly align those without that dummy antenna. Did your SAMS folder say anything about that??? It really should have. It is find to adjust the antenna trimmer with the actual antenna in the car but the alignment is another horse altogether.
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