Philco Tropic 39-770EZ - Printable Version
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Philco Tropic 39-770EZ (/showthread.php?tid=11518)
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Philco Tropic 39-770EZ (/showthread.php?tid=11518)
RE: Philco Tropic 39-770EZ - Ron Ramirez - 02-11-2015
I found that I could pick up the local AM station at 990 kc by placing a finger on the grid cap of the 6J8G det-osc tube. I could also pick it up by placing a finger on the grid of the 6K7G RF tube, but with lower volume. One serious problem, though: 990 was coming in around 650 on the dial, and I could not receive my SSTRAN at all (it's tuned to 660 kc).
Knowing the coils had good continuity, I decided to try performing a complete alignment.
The AM alignment was way, way off. I had to go through the procedure on AM several times, adjusting first at 900 and 1400 kc, then 750 and 1400, and finally the factory recommended points of 580 and 1500 kc. It finally lined up as it should.
Here it is, with the dial scale back in place:
[Image: http://www.philcoradio.com/images/phorum/39-770/39770-59.jpg]
But I am not happy with it. I am no longer receiving the local station at 990 kc (at all). It is picking up on the high end of the band, and picks up my SSTRAN at 660 with plenty of volume, but seems to be deaf in the middle of the band.
The action of the tuning indicator became clear during alignment. Normally, the lamp is lit somewhat dimly. As you tune in to a strong signal, the lamp grows brighter. You tune for the highest brightness on the lamp. Pretty neat.
SW seems to be A-O-K. The highest band, band A (11.6 to 22 mc) seems to be working well with no noticeable issues. Band B (5.5 to 11.6 mc) also seems to be OK. It was too early in the day to really test band C (1.7 to 5.6 mc) although I was picking up a couple signals in the 60m band.
Not sure what to do from here - try probing further, or just let it go and call it good enough.
I really think that part (8), the band C RF coil, has been replaced with an incorrect replacement, and this may be the source of the trouble. The primary of this coil is also used on the AM band. The primary should have a resistance of 80 ohms according to the schematic. This coil doesn't quite match the drawing on the schematic, and its primary has a resistance of 120 ohms. (And maybe this is why the wires of this coil looked like the coil had been removed at some point - maybe it was removed from another Philco set!) I suspect that this may be an AM RF coil from some Philco set.
As always, I'm open to suggestions...a replacement coil is, most likely, unobtainium...
RE: Philco Tropic 39-770EZ - Ron Ramirez - 02-11-2015
I've been doing a little research.
The 39-116 and 39-45 have similar front ends to this 39-770 (only three bands instead of four).
The RF coil for AM is the same part number in all three - 32-2379.
The RF coil for 1.7 to 5.6 mc (32-3106) has a different part number in the 39-45 and 39-116 (32-3054), but the band coverage for that band is very similar (1.7 to 5.8 mc in the 39-45 and 39-116; 1.7 to 5.6 in the 39-770).
The primary of 32-3054 has a resistance of 70 ohms...again, much closer than what is in there now.
I'm wondering if it would be worth the trouble to find a band 2 RF coil from a 39-45 or 39-116 and try it in this 770?
Hmmm...
Well, it isn't something that has to be done now. I think I will put the chassis back in the cabinet and set it aside for now. Later on, I can pursue this issue further.
And when the weather gets warmer, I will paint the power transformer!
Oh, by the way, I also fixed the tone control by switching the two outer wires. Now treble is at the top, and bass at the bottom of the thumbwheel, as it should be.
RE: Philco Tropic 39-770EZ - Ron Ramirez - 02-11-2015
Final thoughts to wrap up this thread:
The more I think about it, the more I like the idea of finding a 39-45 or 39-116 junker chassis for one of those band C RF coils. But that will have to wait for later. And as mentioned in my last post, I'll paint the power transformer when the weather gets warmer.
But for now, some "after" photos.
[Image: http://www.philcoradio.com/images/phorum/39-770/39770-60.jpg]
[Image: http://www.philcoradio.com/images/phorum/39-770/39770-61.jpg]
A close-up of the dial, with the set back together and with the lights out:
[Image: http://www.philcoradio.com/images/phorum/39-770/39770-62.jpg]
Thanks for following along. I am going to devote my time to some needed studies and a few home projects for awhile. I'll have another radio rebuild in the near future; I have not yet decided which one will be next.