12-22-2015, 05:35 PM
Hi all, been away a little too long, and finally getting back to the Philco 89B that's langishing on my workbench. So I had to rewind both the oscillator coil primary, and the second RF coil (between the 44 and 36 tube) primary. The problem is it receives a few stations, then it becomes nearly silent once you tune below about 1kHz. On previous advice, I changed the 36 cathode resistor from 15K to 10K, but it doesn't make much difference. I finally looked at it with my scope, and saw something interesting. When I turn it on, it warms up enough that I start seeing this on the 36 cathode resistor. Looks good, seems to be oscillating!
[Image: http://i636.photobucket.com/albums/uu85/...wFile1.png]
But, wait a couple more seconds, and it's doing this:
[Image: http://i636.photobucket.com/albums/uu85/...wFile2.png]
So the primaries have the same resistance, I took careful notes on how many turns they had and which way they were wound, but it sure seems flaky. Any ideas? I'm starting to get pretty stuck! It's as though this oscillator just doesn't want to oscillate nicely.
[Image: http://i636.photobucket.com/albums/uu85/...wFile1.png]
But, wait a couple more seconds, and it's doing this:
[Image: http://i636.photobucket.com/albums/uu85/...wFile2.png]
So the primaries have the same resistance, I took careful notes on how many turns they had and which way they were wound, but it sure seems flaky. Any ideas? I'm starting to get pretty stuck! It's as though this oscillator just doesn't want to oscillate nicely.
