37-11 Alignment and Sensitivity issues - Printable Version
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+--- Thread: 37-11 Alignment and Sensitivity issues (/showthread.php?tid=13075)
37-11 Alignment and Sensitivity issues - N6MKC - 09-07-2015
I'm working on resurrecting a very neglected 37-11. Finally got it re-capped, re-resistored and mechanically functional again after much de-rusting, cleaning and scrubbing. As you can see in my other posts, I also had to rebuild the set's rock-hard flexible coupler. The set's output transformer had an open primary, but everything else electrically looked good. There were 9 bakelite blocks in this set to melt out and restuff. Quite an undertaking, especially since the wiring to these blocks tends to be very crowded and dense. Anyway, the initial power-up brought static on all bands, but no apparent signals, even with a 60' long wire antenna up about 30 feet.
Since I had disassembled the main tuning capacitor and the mica-trimmer capacitors for cleaning, I figured it would be best to start off with a quick effort at alignment. The IF alignment went without issue, and the set was only slightly off in that regard, but when I started doing the RF portion of the alignment, I was befuddled to see a completely different RF section configuration staring back at me than what's depicted in Riders volume 8 for this set (pages 8-13 to 8-16 in the Philco section). The Rider's shows 3-section compensators for the Osciallator, Antenna and RF sections of the RF chassis. As you can see in the pics, my radio has a different layout. Mine is a Code 125 chassis. Is it possible the Riders information is showing procedures for a code 121 chassis? If so, does anybody have info/procedures for aligning my set? Thanks in advance for any thoughts on this. Oh, by the way, the first step of RF alignment has you inject a signal at 18MC, and I was able to hear that signal, but it was a little weak.
Before:
[Image: http://www.martinihenry.com/temp/37-11x/beforesm.jpg]
After:
[Image: http://www.martinihenry.com/temp/37-11x/after.jpg]
RF Subassembly underside…
[Image: http://www.martinihenry.com/temp/37-11x/rfchassis.jpg]
What Riders says I should see…
[Image: http://www.martinihenry.com/temp/37-11x/riders.jpg]
It's my code…
[Image: http://www.martinihenry.com/temp/37-11x/code.jpg]
RE: 37-11 Alignment and Sensitivity issues - Radioroslyn - 09-07-2015
Hi Jason,
I'd drop Chuck a note:
http://www.philcorepairbench.com/
Nice projects, you might find that a VF-1 may replace FT-171s.
Terry N3GTE
RE: 37-11 Alignment and Sensitivity issues - N6MKC - 09-09-2015
Service bulletin 268A would appear to contain my salvation. It's on its way from Chuck. Thanks for the suggestion. Will keep you all informed of how it goes.
RE: 37-11 Alignment and Sensitivity issues - morzh - 09-09-2015
Neglected it was indeed, nice job leaning it up!
RE: 37-11 Alignment and Sensitivity issues - Crist Rigotti - 09-09-2015
Nice job on the restore!
RE: 37-11 Alignment and Sensitivity issues - N6MKC - 09-22-2015
Okay, many thanks to Chuck for setting me up with the correct documentation for the radio. Sure enough, Service Bulletin 268a contained all the needed secrets. What a difference the correct documentation makes!
On my sensitivity issue, turns out, my problem is an open RF coil between the RF amplifier section and the Detector/Oscillator section. It's killing the sensitivity on bands 1 and 2. Of course the open is in the super-fine 6.5Ω section of the coil, and not the thick, .5Ω section that would be super-easy to fix. I unwound some of the wire from both ends of the 6.5Ω section, and the break is sadly not near the ends as I had hoped. Looks like I'm in the market for a replacement…
http://philcoradio.com/phorum/showthread.php?tid=13163
Interestingly, the Code 125 RF alignment instructions have you start at 1600kc, versus 18mc on the Code 121 chassis.
RE: 37-11 Alignment and Sensitivity issues - klondike98 - 09-22-2015
very nice job!
