[Eric Adams]

Jerry,
The AM works great. I did an alignment and it pulls in my favorite test station: WSM from Nashville. The trebel squeels as I turn it up. FM has no sound at all.
The reason I mentioned the pushbuttons was because FM is a pushbutton also. Since I found 2 of the pushbuttons for AM don't work I figure since they are the same mechanism, I may be on the right track.

[Eric Adams]

Latest update: All AM pushbuttons are working, just needed adjustment. When on FM, if I tap any part of the chassis, I can hear the tapping in the speaker. It almost sounds like there is a mic connected to it. I rechecked the FM1000 tube and it is good. Any thoughts?

Thanks,
Eric

[jerryhawthorne]

Eric, your on course! The little tapping indicates either a very microphonic tube or perhaps a bad connection. If the only place you find it is on the FM 100 tube, clean the tube pins and the socket with something like Deoxit or even WD 40. A little of that on the base of the tube with some fine steel wool. Clean off the base well with some clean rag to assure no steel wool remains and then insert multiple times in the socket. Could be just a bad connection between the two. Of course it could be the tube, but I doubt it.
Jerry

[Chuck Schwark]

Still maybe one or more microphonic tubes or

Possibly the tuning gang rubber mounts are petrified and causing the capacitance of the tuning gang to change in response to the vibrations. At loud audio levels this can also cause a feedback "howl" sometimes due to speaker vibrations. Your tapping does the same thing. Try lightly tapping the tuning gang to see if it's the cause.

Just two things to try.

Chcuk

[Eric Adams]

Thanks guys, I do get a feedback howl when I turn up the treble at higher volume. I'll be digging into it.
Eric

[Eric Adams]

I got it! After retesting the tubes (My tube tester has a place to put headphones to listen for any sounds the tube might be making) I found one disc cap, .01 that made some noise when I touched it. I replaced it and now have FM! I also put another .01 cap in the treble circuit. It still gives me some treble but the squeal is gone! One final alignment and I'm done.

Thanks to all for your help,
Eric

[Eric Adams]

Well... FM quit again but the good news is that I really found it this time. You guys were right.The rotary switch that controls FM has a lever that pushes on it from the pushbutton. This lever holds on to the shaft of the rotary switch. If the set screw for the switch isn't tight, the switch won't line up! So, it's tight now and I can finish the cabinet and I'm done.

Thanks again,
Eric