40-190 image tuning, need help - 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: 40-190 image tuning, need help (/showthread.php?tid=769)

---

40-190 image tuning, need help - BDM - 09-27-2007

Hello all. I've been lurking for some time now and decided to try my luck. I have issues with a few Philco's, but I'll start with this one

I've recapped, replaced a few resistors that were out of tolerance. Completely aligned the set and I cannot solve this issue. When tuning stations at the low end of the BCB, you get the station at two different spots on the dial. I'll try to explain this best I can. Example, I tune in 540/kc. As you tune up, the station sort of fades away as it should, then re-tunes again on 550/kc. Almost as strong as on 540, and it sounds slightly different. It does the same thing to stations as you tune up, but the "effect" starts to disappear after 600/kc, and seems to be completely gone by 650/680 kc. The receiver is sensitive, and this effect doesn't occur on the SW bands. One other thing, if you null the received station(weakening it), the effect is also gone or noticed very very little.

I've tried tuning and re-tuning the IFs. I've dropped the IFs to both a low & higher freq setting, this has little effect. One thing I've noticed is IF 37A seems flaky. Meaning it doesn't tune sharp. It seems wide possibly. I'm no expert, but considering the IFs I've tuned in the past. It just doesn't seem right. Any ideas I may be missing. It's driving me nutty
Here's the schematic
http://www.nostalgiaair.org/Resources/339/M0013339.htm

Thanks gents.

Brian

---

- rickd - 09-28-2007

Just guessing here. Does the set show the same problem when setting a button to that station? Sometimes it seems the tuning caps lose their "cordination" a little on the low end. Any visible damage to the tuning cap?

---

- BDM - 09-29-2007

No, tuner is very clean. No bent plates. I did check for that.

---

- Ron Ramirez - 09-30-2007

I would take a serious look at that 2nd IF transformer (37). I would bet it is faulty, since you are unable to peak its trimmer at 455 kc. Bear in mind also that the AVC filter network (37B, 37C & 37D) are inside the IF can.

Many different 1940 or 1941 Philco chassis will yield the IF can you need to replace it; just be sure the replacement can has the AVC filter network inside. I see 40-150/155/180/185/190 chassis on eBay frequently, as well as 1941 model 41-250/255/280/285/287/290/296 chassis.

Once replaced, realign your radio for a 455 KC IF.

Good luck.

---

- BDM - 09-30-2007

Thanks Ron. I have a 40-155 that also has issues. But that set is so clean I can't part it I'll hunt another parts set down.

Brian

---