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RCA A-39 (Canadian build)

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Post by Spectre Sat Mar 27, 2021 10:21 pm

Hi all.

I'm in the final stages of restoring an RCA A-39. The last thing to restore is the push button function. The radio itself is working beautifully.

I'm not having any luck with the push buttons (PB's). I've watched a very informative video about those very PB's and have followed the instructions to a "T". But the radio for some reason won't let me adjust the cores and trimmers to pick up any stations.

I have been able to tune to each PB to a frequency that I inject through the antenna contact, or by just draping the probe from the frequency generator over the antenna coil. However, once tuned to a frequency, say 740 khz, once I remove the generator probe, the radio falls silent. Yet on the a.m. band, the stations are picked up easily.

Does anyone have any experience with the PB's that I'm talking about? The radio is from circa 1941. The same PB'S were used in Westinghouse radios of the same vintage.

Thanks!
Joe

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Post by Dale H. Cook Sun Mar 28, 2021 12:56 pm

Are you using the absolute minimum generator output, with the generator coupled to the antenna input through a small cap or dummy antenna, needed to get just enough audio output to adjust the PB circuit? Do you have a URL for that video so that we can see if it is correct?
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Post by Spectre Sun Mar 28, 2021 3:27 pm


https://
youtu.be/wJ0jFE255OY
Here's a link to the video.   And no, I wasn't using the lowest output.  I'll try that to see whether it works.  Thanks!

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Post by Spectre Sun Mar 28, 2021 7:15 pm

Ok, this is weird.... I spent literally hours working on this push button problem- I was receiving nothing, and attempted to tune the cores using a signal generator...... all to no avail. I needed to wrap up this project, so I reassembled the radio today. Once all together in the cabinet, I thought I'd try adjusting the cores again and got the signal generator ready. But, to my astonishment, as I started tuning the first core (without using the signal generator) the stations started to roll in. I was able to tune all 6 pre-sets in a matter of minutes. What could have happened that didn't let me tune on the bench, yet let me tune in the finished radio?

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Post by Dale H. Cook Sun Mar 28, 2021 8:42 pm

Spectre wrote:I wasn't using the lowest output.
Whenever doing any alignment you always need to use the least amount of signal possible. When you tried it off-air you had very low level signal inputs, and that allowed you to adjust things properly.
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Post by Dan Walker Sun Mar 28, 2021 10:56 pm

It is possible that you had the three prong antenna plugged in, or maybe there was something that was not grounded until you put it in the cabinet.
at least now it works.
Dan in Calgary

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