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Not specific to the 116, but typical AVC voltages I usually develop on similar Philco's with an RF stage is -10 to -15 volts with a strong signal. You may get a bit different readings but they should be in the ballpark.
If the antenna trimmer has no effect, I would suspect some problem with the antenna coil or bandswitch, especially if the developed AVC voltage is low.
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I am getting half the voltage you mention. Will have to keep looking.
Gregb
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Greg, you might try connecting the antenna directly to the grid cap of the 77 mixer or 78 RF tube and see how the sensitivity and AVC voltage compares. By bypassing the ant and RF stages, you can see if there are excessive losses from these circuits.
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I gave that a try Mondial and it made the reception very distorted with lots of hum and the AVC changed very little.
Gregb
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Perhaps a better suggestion would have been to use a signal generator to inject a known level signal into the RF stage and mixer grids through a small coupling cap while leaving the original grid cap wire in place. I just noticed that the mixer grid is RC coupled, with a 2 Meg resistor to ground. This would make it a very high impedance circuit which would be susceptible to hum pickup, especially from a long wire antenna.
Does the antenna resonant circuit fail to tune on all bands or just AM broadcast? I could see it possibly tuning somewhat broadly, but the trimmer having no effect at all is a bit suspect.
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In the mean time I was doing some further checking and found a bad mica cap, #33, 250uuf. I changed it out and the adjustment problems cleared up as well as another problem I had noticed. When I would tune to a weak station I would hear it and all of the local stations as well, not any more. Everything tunes fine and the antenna circuit seems to be adjustable now except the high short wave band, it is adjustable but very broadly. The AVC issue is still there with no change. I have checked all of the mica caps around the 2nd detector tube as well as resistors and all seems good. I installed a new #37 tube with no change.
Gregb
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One more thing you might try is changing the 78 RF and 1st IF tubes. If one of these has excessive gas it will cause positive grid current, partially cancelling out the negative AVC voltage. I once had this problem with my 89, where the AVC never went over -4 or -5 volts. With no antenna connected, my AVC line was slightly positive, and only went negative on a strong signal.
How does your shadow meter seem to operate? Do you get good deflection and a narrow shadow with a strong signal?
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I will try swapping out the tubes as suggested. One thing I did notice on the AVC is with no signal in a quiet area of the dial the most positive it gets is -3 volts. The shadow meter does not work at the moment and I did check the coil and it measured 2400 ohms.
Gregb
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Well I gave your suggestion a try and I hate to admit this but I made a super amateur mistake. I transposed the 77 and 78 tubes, the numbers were just about gone and guess I just didn't look close enough. Radio works perfect now and everything lines up just fine. I cant believe I made such a silly mistake! On to the shadow meter now and then final cleaning and back into the cabinet.
A valuable lesson here is always check the simple stuff first!
Gregb
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Congrats on finding the issue! Don't kick yourself for making a mistake. be glad it was really easy! I just recently had a bout of stupidity and misread a 27K resistor as a 27 ohm on a B+ line. (do not ask how I mistook Black for orange, it was late). thankfully I started my troubleshooting @ the Rectifier and found it without much time spent. b+ shot up from 60 to 113 volts after the change..
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Thanks for the pat on the back, your right, simple mistake and easily made. Good news is the shadow is working though not sure if it is as good as it could be. Wide open is about 3/8" and when on station it is a thin line, should it go wider?
Gregb
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you're welcome! I've got a late 35 16B shouldered tombstone chassis code 125. in Queue over here.. I'm sure I'll be on here with a post or two when I get to it!
I've watched a few video series on YouTube about shadow meters. seems to me it should be a sliver, like you have, when it's tuned in. none of them seemed to open very wide when out of tune.
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I have watched some of those videos as well and if I don't hear different from anyone before the new dial scale arrives I will keep it the way it is. Oh and I have to order new rubber chassis supports as well.
If I am able to provide any support for you on your 16B I will chime in. Next one up for me is the 15X I got from Willie.
Gregb
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Sweet, Thanks! First I have to go back to a radio I had to completely rewire last spring. and since some of it was missing, I inevitably got some of it wrong.
