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 Post subject: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 2:54 pm 
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I purchased an Arvin 58A and the previous owner changed the entire tube layout, wiring, field to PM speaker, etc. (link to original circuit): www.nostalgiaair.org/pagesbymodel/563/M0012563.pdf The original tube layout now has: 1 12SA7, 2 12SK7, 12SQ7, 35L6 & 35Z5. (No, I didn’t know it had been so modified when I purchased it!). The problem I having is: On the lower end of the AM band, 750 kc comes in at 900 kc, the upper end of the band is somehow relatively more accurate, though obviously not tracking correctly. I’ve checked & replaced several OOT resistors and a couple of wax bypass resistors left behind (all else is good/new). I’ve aligned the IF’s (even tried several different frequencies to see if that was the problem). I’ve aligned the tuning capacitor (which I suspect was also replaced) as I would any other set, but can’t remedy the discrepancy in tuning. Like the rest of you, I’d rather have a set “untouched” and original than to open up a “bucket of worms.”

Any help would be appreciated. Thanks!

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 5:38 pm 
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It looks like someone wanted to make it a standard AA5 set to get rid of the ballast tube and old PM speaker. They didn’t even use a 50L6 output tube.

The first thing that comes to mind is that a different Oscillator/Converter tube may not have the same specs as the original. This could effect how it works with the oscillator coil, thus the alignment.

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 5:54 pm 
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In the alignment procedure, Operation 2 is the only step I see to get the dial to track normally. Can you locate those adjustments on your set? If you haven't tried that yet, it should be your first step.

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 8:48 pm 
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processhead wrote:
In the alignment procedure, Operation 2 is the only step I see to get the dial to track normally. Can you locate those adjustments on your set? If you haven't tried that yet, it should be your first step.


Yes, absolutely. I did that in the beginning. An AM broadcast transmitter upstairs that’s set on 1450 kc is 1450 kc on my dial, but a local 750 kc station is at about 910 kc. I can’t get the tracking right on the lower end of the dial. This one is a real “hack” job. :roll:

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www.sarsradio.com
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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 8:56 pm 
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Dnitram wrote:
processhead wrote:
In the alignment procedure, Operation 2 is the only step I see to get the dial to track normally. Can you locate those adjustments on your set? If you haven't tried that yet, it should be your first step.


Yes, absolutely. I did that in the beginning. An AM broadcast transmitter upstairs that’s set on 1450 kc is 1450 kc on my dial, but a local 750 kc station is at about 910 kc. I can’t get the tracking right on the lower end of the dial. This one is a real “hack” job. :roll:


Sounds like they worked that set over good. With so many mods, you are kind of out there on your own, and the service literature may or may not apply.

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Sun 16, 2019 11:08 pm 
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This is crazy! Just tacked in a Meissner adjustable oscillator coil and having it track pretty well. Going to mount it, readjust and call it a day. Thanks for the input and suggestions!

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www.sarsradio.com
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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Mon 17, 2019 12:48 am 
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I’m glad you got it working. It’s very frustrating when someone modifies a radio and it can’t be easily put back to normal.

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Mon 17, 2019 1:11 am 
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Great job working around the work around. :D

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 Post subject: Re: Arvin 58A Not Tracking Right – Need Help
PostPosted: Jun Wed 19, 2019 4:45 am 
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Location: Lexington, KY USA
The 12SA7 and 6A8 normally have different oscillator circuits. What sort of circuit was in the set when you got it? Perhaps the coil had been changed.

Probably, you might have taken turns off the coil to align the oscillator near the bottom of the dial. You might have then needed a bit of extra capacitance across the tuning cap gang to restore the calibration at the top of the dial.

The drawing of the chassis top shows a cut-down oscillator gang on the tuning cap, so no padder should have been required, but perhaps adding one would have also fixed the problem.

The adjustable replacement coil makes for a straightforward solution.

Modified sets can be an adventure!

Ted


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