37-9 - Printable Version
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37-9 - tomg - 04-08-2022
Having recently completing a rebuild of a 37-9 I have some questions concerning tuning.
The electronics are actually a combo of a 37-9 RF assembly and a 37-10 audio/power supply and a 37-10 if assembly.
After replacing the caps, resistors, rubber mounts and a coil repair I was able to pick up a couple of very weak stations.
I have never aligned a receiver before but was able to do a if alignment that brought in brought in stations very well.
The first if coils peaked nicely as did the 2nd if primary adjustment. However the trimmer across the secondary of the second
if bottom out (tightened down) before peaking and dropping back down. Any thoughts as to my next step to improve this adjustment.
When aligning the dial the procedure says to place the 520 K. C. mark midway between the index line and the glowing beam.
I'm not sure what they mean by the "index line". The rest I understand.
I will probably need some advice as to tuning the b ands but will wait till I get this correct first
I am using a HP 3312A function generator and HP 465 scope to align as I do not have a VTVM at this time.
Any help is greatly appreciated.
Tom
RE: 37-9 - Mondial - 04-08-2022
How accurately are you setting the function generator to exactly 470 kHz to align the IF? Do you have a frequency counter to accurately check the frequency? If the generator is slightly low in freq, the trimmer may not have enough adjustment range.
Without a frequency counter you can confirm frequency accuracy by listening for the second harmonic of your generator ( 940 kHz ) or third harmonic ( 1410 kHz) on an accurate digital AM radio. Setting the function generator to triangle will produce higher harmonic content for a stronger received signal.
RE: 37-9 - tomg - 04-09-2022
I've been using the scope to measure 20 cycles of 470 khz but looks like I need to get a counter to be accurate enough.
I want to tune a couple of other radios I've restored but will wait till I have an accurate way of setting the generator.
For now I'll try to set it by using the radio in my car. Thanks for the reply and tip about the triangle wave setting.
By searching the forum I found the info required to fix the muting switch which now works and the dial now moves smoothly.
Mechanically everything functions, magnetic tuning works and even with a less than perfect antenna I can pick up a couple of
stations in the upper bands. Getting the tuning correct will be the finishing touch.
Do you have a suggested counter to use? Still not understanding the mechanical alignment of the dial. The "index line" is still
not sinking in.
RE: 37-9 - mikethedruid - 04-09-2022
Actually, I use a good digital readout shortwave radio to check my sig gen output. For the IF, I tune on the regular AM band to TWICE the desired IF frequency. I set the sig gen to the desired frequency, in your case 470 KC, and then tune the radio to 940 KC, and adjust the sig gen for maximum loudness through the radio of the modulated output from the sig gen. Then I proceed with tuning the IF. It is another way around the problem if you already have a good, accurate digital readout radio.
RE: 37-9 - Mondial - 04-09-2022
Tom, regarding setting to the index line, see page 5 of the attached service info of the 38-116. It shows a detail drawing of the dial with the glowing beam set to the index line, which is the last vertical line of the dial calibrations.
Follow the dial set procedure of your model, not the attached info, which is only given for reference to show the dial detail.
Hope this helps.
https://philcoradio.com/library/download/service%20info/service%20bulletins/Philco%20Service%20Bulletin%20286.pdf
RE: 37-9 - tomg - 04-09-2022
Thanks Mondial that makes it clear. Mikethedruid I did as you suggested and got a good clear signal at 940 and 1410 on a digital radio.
I'll redo the if alignment using the generator at this setting.