The PHILCO Phorum
Alignment. - Printable Version

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RE: Alignment. - fields 100 - 10-05-2014

Pete,

Thanks, I will check the plates and report. Funny, I did not use the 10 turns coil, just connected the counter via 40 pF cap and it did show +455 K.C. How do you adjust the plates though?

RE: Alignment. - Radioroslyn - 10-05-2014

You bend them.
Terry

RE: Alignment. - Mondial - 10-05-2014

Fields, do not connect the counter directly to the grid of the 6A7. As mentioned previously, you are adding almost 40 pF capactance to the tuned circuit which will lower the actual freq. Use the 10 ten turn pickup loop as suggested. Regardless, the counter will always read 455 kHz higher because that is the IF offset, so all that indicates is that the IF is properly aligned..

What you really want to do is to check the full tuning range of the oscillator. With the tuning cap fully meshed, measure the freq. It should be 540 + 455 or about 1000 kHz. Then open the tuning cap completely and measure again. You should be at about 1700 + 455 or 2150 kHz. Adjust the J trimmer to set the low end, and the osc trimmer F for the high end. By going back and forth you should have both ends of the band at the right freqs. At that point, the dial calibration should agree across the band.

While the tuning cap plates can make small changes in freq, I doubt that much error can be attributed to bent plates. Just make sure the rotor and stator plates are centered within each other.

Your real problem may be the antenna tuned circuit is not tracking the osc. If you have been trying to align the padder trimmer J for max signal at 600 kHz and the ant circuit is off, then you have been misaligning the osc to compensate, causing the dial cal to be thrown off. You need to make the osc agree with the dial markings before trying to peak for max received signal.

RE: Alignment. - AI2V - 10-05-2014

One more important thing to note-  "moding" of the oscillator.  It's something you need an oscilloscope to see.  What it comes down to is a form of distortion that will change as you alter the frequency.   At one end of the dial the oscillator will be a sine wave but as you tune down, distortion begins and ultimately there is so much distortion that the counter will measure harmonic mixes.  Fixing "moding" is fairly easy by making sure the voltages are good  or the osc feedback may need to be increased/decreased.  Don't jump in and start tampering unless you've proven that your signal is distorted.

RE: Alignment. - fields 100 - 10-06-2014

So, first I checked the tuner's plates, there was no shortage. Then I made the loop and checked the +455K.C.It is OK in the middle of the dial but gets worse getting to the lower side of the one.At that time my J trimmer was maxed out and the frequencies were matched with the pointer with about 15K.C. discrepancy.Not correct but not terrible. So now, to get 955 K.C. (540 +455) I had to bring the J trimmer 1/2 way down it's travel, quite an adjustment. After that checked the 800K.C station -it was at 650 on the dial. In another words- same issue as before.
I have a question- does getting +455K.C mean that that osc. coil is wound correctly? I have heard, that even slight change in the gauge may affect the coil operation. Also, I had not mentioned that before, original coil, after the 60th turn had 1/8" gap, then the rest of the wire was wound. Does it make any difference that I did not maintain such gap?

RE: Alignment. - Mondial - 10-06-2014

Fields, do not confuse the 455 kHz IF offset with the proper osc frequency. The osc will ALWAYS be 455 kHz higher than the actual receive freq in your radio, provided the IF was aligned properly. What is important is that the osc covers the full range necessary. Did you set the osc to 955 kHz as you mentioned for the low end or the correct 540 + 455 = 995 kHz?

It is very important to rewind the osc tuning coil EXACTLY as the original, because any difference in geometry will affect its inductance and therefore its tuning range and accuracy. It is not like rewinding the usual tickler coil as in most Philco coils. The tickler coil is not very critical as to wire size, number of turns, etc, but the resonant tuning coil is critical in your case.

To me it seems as if the inductance of your coil is low. I get this impression because for you to get the osc to operate at the right freq at the low end, you have to screw the J padder trimmer in completely. This indicates that more capacity is needed to make the coil tune because the inductance of the coil is too low.  If I were working on it, I would try adding another 10 turns to the existing winding, and see how it then behaves.

RE: Alignment. - fields 100 - 10-06-2014

Mondial,
Yes, I did set it at 995 with the dial at 540. I think you are absolutely right that I screwed up that coil. I even heard that the best and only way to deal with a problem is to get replacement coil for this particular radio. I will add those 10 turns, see what happens and report. Thanks so much.