Antenna Trimmer - 1956 Wonderbar AM radio

[Patrick Fant]

My 1956 4-dr sedan has a working AM Wonderbar radio.  Trying to locate the ANTENNA TRIMMER - a small screw adjustment they had on these radios that helped tune the antenna to the best band width range for the stations most listened to in your area.  Does anyone know where to locate this little adjustment?  pat fant CLC#31723

[J. Gomez]

My 1956 4-dr sedan has a working AM Wonderbar radio.  Trying to locate the ANTENNA TRIMMER - a small screw adjustment they had on these radios that helped tune the antenna to the best band width range for the stations most listened to in your area.  Does anyone know where to locate this little adjustment?  pat fant CLC#31723

Pat,

Bottom right side just below the antenna jack.

[PHIL WHYTE CLC 14192]

If the radio is working correctly I would not touch the trimmer. I may be wrong but I believe you would adjust that in conjunction with a signal generator.

[J. Gomez]

If the radio is working correctly I would not touch the trimmer. I may be wrong but I believe you would adjust that in conjunction with a signal generator.

Phil,

The antenna trimmer can be slightly tweaked with the radio install and the antenna fully extended, usually on a weak station between 600Kc and 1000Kc for maximum volume. This is done once the radio is properly aligned on both the IF and RF sections.

So if the radio IF and RF are not properly aligned adjusting the antenna trimmer would not be of any help.

So you are correct the main tuning for it is done during the alignment process with a signal generator as part of the RF section for the 1615Kc side.   

[bcroe]

The whole reason for the ant trimmer is to compensate for whatever
antenna may be plugged in, so by definition it is done in the car.  It
typically is done closer to the high frequency band end (where it has
more influence) on a weak station, but it could be used to favor a
particular favored single station. 

Just finished rebuild of a 39 here.  Bruce Roe

[Patrick Fant]

This is very helpful - thank you.  We've adjusted the trim a bit and it has not made much difference.  Have a lot of ignition noise in the audio that I hope to filter out with a noise filter capacitor at .5 micro farad.  I am told that it would go between the battery and the alternator (it has one now.)  I want to check on that positioning however as  I am not sure that would be right place to wire in. pat fant

[J. Gomez]

This is very helpful - thank you.  We've adjusted the trim a bit and it has not made much difference.  Have a lot of ignition noise in the audio that I hope to filter out with a noise filter capacitor at .5 micro farad.  I am told that it would go between the battery and the alternator (it has one now.)  I want to check on that positioning however as  I am not sure that would be right place to wire in. pat fant

Pat,

There should be two 0.3mf one at the generator on the "A" terminal and one at the VR on the "Batt" terminal. These would be a bit hard to find but if you have the 0.5mf they should be fine.

Now one note on these old radio noise suppression condensers/capacitor, they do tend to go bad with age so you may need to try a few and hope for the best. In my case I just remove the guts inside the can and replace them with new regular capacitors.

Good luck..!

[bcroe]

If the noise is there with the volume turned all the way down, it
is coming into the radio via the wiring.  There are filters inside for
this, but needed replacement on the 39 I recently overhauled. 

If the noise comes up with the volume control, and is much
worse on weak stations, it is coming in the antenna from
radiated noise.  An internally regulated alternator should make
noi noise at all, you could try that cap from ground to the stud
but doubt it will help.  An alternator with an external mechanical
regulator can generate noise, should already have a cap at the
reg, takes shielding to contain (good reason to to use this type). 

Ignition noise is difficult.  I believe the car has a cap at the PLUS
side of the ignition coil, try yours there.  NOT on the minus side
going to the distributor.  After that you are into resistance plugs
and/or resistance plug wire.  Aircraft type complete shielding
works, if you can afford it, HAMs use it.  There are other sources,
motors you turn on, a cap at the 12V terminal is usually effective. 
good luck, Bruce Roe