model 42-322 audio distortion - 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: model 42-322 audio distortion (/showthread.php?tid=670)

---

model 42-322 audio distortion - Guest - 06-18-2007

now that the restoration is complete with all caps replaced and deteriorated wiring redone, followed by a complete alignment, it receives stations on bcst and sw just fine. all tubes test good.

now the problem is the hum that was there before the restoration is even worse. on strong stations it doesnt just hum but it gurgles. the stronger the stations the worse it is.

would it help if I paralleled the filter caps with a higher value? also, would it help if I tied the negative side of the filter caps to the chassis instead of the end of the filament string? oh, I also found out you cannot tie the chassis to ac ground. it quickly blew the fuse I put in the ac line.

guess I need a refresher course in ac/dc radio theory and a good book on troubleshooting and modifications would sure help, along with a copy of the technical bulletins.
regards, Dick

---

- rickd - 06-20-2007

Lotsa guys here going to have better advice than me, so I'll just say it's probably not anything to do with your power supply filters. Does it get worse when you tune in a strong station regardless of volume level or anytime the volume increases? Trying to get an idea if it's in the audio section or the rf/if/det string. Did it do it with the alignment signal?

---

- planigan - 06-20-2007

kf4ns, Hi, don't parallel the electrolytics, you will put a strain on the rectifier. The electrolytics should not be grounded to the chassis they should be isolated from it bu sleeves or isolated mounting plates. I think you have a shorted cap somewhere since, depending on the size of the fuse, grounding the chassis should not cause a short. PL

---

- Guest - 06-22-2007

Well guys, I found the trouble. It is one of my most embarrassing moments. For someone with my experience and qualifications in electronics I should be tarred and feathered.

I had added a single terminal of a terminal strip just to have a place for the ICL (inrush current limiter) and used a very strong glue called shoe goo to hold it to the chassis. I failed to notice that the rivit in the back was touching the chassis. I HAD TO HOT LEAD OF THE AC GROUNDED TO THE CHASSIS. What a dumb mistake!

With it now ungrounded the radio plays BEAUTIFUL and really pulls in the stations with remarkable clarity. NOW the project is done.

Thanks to all for the support. This was a very interesting project. My first excursion into the relics of the early 40's.
Best Regards,
Dick KF4NS

---