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Trouble Aligning 116B-121 IF - Printable Version

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Trouble Aligning 116B-121 IF - JWD - 10-01-2012

I'm having trouble aligning the IF stages of a 1935/36 116B-121 Tombstone, (2nd Detector, 2nd IF, 1st IF). It's been recapped and out of spec resistors replaced, but I'm not getting much deflection on the shadow meter and the AVC voltage is about half what it should be.

What I noticed while doing the alignment is that the tuning slugs want to be turned all the way down for maximum output voltage. And even bottomed out I don't pass through a peak voltage point.

I have not replaced any mica caps, but the only ones I see in the IF stages are the variable mica caps to trim the coils. Resistance in the coils checks out.

I've tried removing the 3 IF cans to have a look, but haven't figured out how to do it. They look to be spot welded together and must come out as a unit. Would appreciate any tips on freeing all three retaining clips.

Any ideas on what to try next would be very much appreciated.

John

RE: Trouble Aligning 116B-121 IF - TA Forbes - 10-01-2012

Hello, John: have you checked the shadow meter coil itself?

You have to use a pair of pliers to squeeze the clips to pass through the hole. I use a thin screwdriver between the can and the chassis as I get the clips loose.

RE: Trouble Aligning 116B-121 IF - JWD - 10-01-2012

Hi TA Forbes,

The Shadow meter checks out ok. My biggest concern is not being able to align the IF properly. I believe the Shadow meter / low AVC voltage is just a symptom of being out of alignment. But, as mentioned above the variable mica caps bottom out before reaching the optimum output voltage.

As for removing the IF cans, unfortunately all three are connected, and can not be removed separately. The difficulty I am having is in getting to all three clips.

Thanks,
John

RE: Trouble Aligning 116B-121 IF - Steve Davis - 10-01-2012

John, to me it seems unlikely that you would be unable to peak all three IFs. Are you sure your signal generator is set to the correct frequency?

Steve

RE: Trouble Aligning 116B-121 IF - JWD - 10-01-2012

Hi Steve,

I am able to peak the 1st IF. I'm having trouble with the 2nd Detector and 2nd IF. I'm using an Eico 324 which has been calibrated using a radio. I then checked a few other radio stations to see how well it tracked across the frequency band range and noticed some error.

Since I don't have a frequency counter yet, I took some data points of the frequency error across the Standard Broadcast band and plotted it on an excel spread sheet to give me a guestimate of offset for 460kHz, (about 7kHz offset). I set the 324 accordingly and did an alignment.

I would think even if the reference frequency was off a bit there would be enough adjustment in the trim caps to peak the output voltage.

John

RE: Trouble Aligning 116B-121 IF - TA Forbes - 10-02-2012

I would find a freq counter, there are many on eBay and other places and they are very affordable.

Aligning with the wrong f can make for some unpleasantness. Don't ask me how I know that.....

RE: Trouble Aligning 116B-121 IF - codefox1 - 10-02-2012

+1

Info here:
http://www.nostalgiaair.org/PagesByModel/122/M0013122.pdf

I believe I would just follow the alignment procedure in exact order given and try to determine a point of failure. IF is 460 KHZ for this one.