Philco 41-258 Hum - 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 41-258 Hum (/showthread.php?tid=1570)
+- 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 41-258 Hum (/showthread.php?tid=1570)
Philco 41-258 Hum - Guest - 12-20-2008
Hi folks. This is my first time here on the forum. I need a little help with a 41-258 floor model. When I got it back in October, the set was ALL ORIGINAL! So, you know what that means. I have spent the last month installing all new wire and components. The only original parts are the mica padders, tuning cap, and the coils. Each coil form had new wires attached to the base. All coils have been checked for continuity. However, when I fired it up tonight, I am getting a severe hum on top of the incoming stations. I am getting a strong signal from the local AM station, and I am able to tune. But, the hum disappears when I turn the volume down. So, I believe the new filter caps are doing their job.
I tried the old "grounding the screen grid" trick to isolate the stages, along with my signal tracer. I am almost certain that the first two stages are clean. The first IF 7B7 has a good clean signal coming off of the plate. But, I can't seem to pin down where the hum is coming from. I think it is somewhere around the 7C6 Detector. Does anyone have any ideas? Thanks.
Re: Philco 41-258 Hum - rghines1 - 12-21-2008
Hi,
Sure did a lot of work!
Verify the negative leads of the power supply caps were not connected to the chassis. Schematic shows they connect to a separate B- bus that floats above the chassis.
Richard
Re: Philco 41-258 Hum - Guest - 03-06-2009
Hi folks. I just wanted to update the post. It turns out that I had a couple of B- lines going to locations other than the cathode pin of each tube. Someone before me removed a couple of the lines, and never put them back. So, after a little guesswork, I got the set to play without the hum. Thanks to Richard for your help.