Philco 38-7 Oscillation - 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: Philco 38-7 Oscillation (/showthread.php?tid=25414)
+- 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: Philco 38-7 Oscillation (/showthread.php?tid=25414)
Philco 38-7 Oscillation - tludka - 11-26-2024
I have let this one sit because of other duties. Now I am back, and I have a couple of questions. I hooked up a Hammond 125BSE audio transformer to a 4-ohm speaker. I receive a crackle and the putt- putt like a bad filter cap. Since the original speaker was not with the radio, I am using a 1200-ohm resistor for the field coil. The voltage checks from the Philco spec are close to the specs except for one of them. The filter caps have been replaced. If I remove the cap lead from the IF 6K7G tube the reading on the plate seems ok and the putt putt stops. When I attach the cap the reading Justs fluctuates and will not stabilize, and putt putt is back. The cap reads a negative 3vdc disconnected from the tube. I have checked all the resistors and replaced the caps. Checked the wiring several times. The 1st I.F. coils ohm out per the schematic but not sure about the mica caps in it. Could this be the problem?
RE: Philco 38-7 Oscillation - morzh - 11-27-2024
Usually in this forum, when we discuss a radio, we do not multiply threads. You already have a thread on this.
If you want the thread to not be exclusively about the speaker, simply rename it into 38-7 restoration or something like it.
Renaming is easy.
RE: Philco 38-7 Oscillation - Radioroslyn - 11-27-2024
As to your oscillation issue I would align the IF transformers. That may solve the problem. You also would want to check the ground connections that are made thru rivets as those can be faulty over time. Check all of the parts in the avc line as the oscillation can get into other stages.
RE: Philco 38-7 Oscillation - tludka - 11-27-2024
Will do, thank you.