46-1226 run 122 with squeal - 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: 46-1226 run 122 with squeal (/showthread.php?tid=2745)
+- 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: 46-1226 run 122 with squeal (/showthread.php?tid=2745)
46-1226 run 122 with squeal - Jim Dutridge - 12-21-2010
This radio has been recapped and all OOT resistors replaced. When brought up on a variac with the volume control turned completely down, the radio will squeal loudly once the current draw reaches around 460ma. If I turn the volume up slighlty the squeal will stop, but returns has the current draw continues to increase.
I have not moved any wires except for extending 2 B+ lines to reach the new terminal strip holding the replacement filter capacitors, and these were run right next to the chassis. I suspect I might have a bad volume control but I don't know what the value of the tap is. Right now it measures just over 1 MEG on this 2 MEG control. The Sams, 15-24, does not show the value. The part is an original Philco part, #33-5535-1. Anyone know what the tap value should be? Thanks.
Re: 46-1226 run 122 with squeal - Ron Ramirez - 12-21-2010
Hi Jim
The original was 2 meg. overall, tapped at 1 meg.
Is R202, 4.7 ohms, connected to the bottom of the volume control, properly grounded at the other end, and in tolerance?
Re: 46-1226 run 122 with squeal - Jim Dutridge - 12-21-2010
Thanks for the reply Ron. Yes, the 4.7 is new and connected to the bottom side of the control to ground. So, my volume control is OK then. One thing I did find is that the 33K resistor #54 in the Sams print, was connected as shown in the Riders for the run 121 chassis, at the tap. The Sams shows it connected to the bottom side of the control.
I removed the tap connection for the resistor and placed it on the bottom of the control but it still squeals. If I keep the current draw below 460ma I can get normal audio from the radio, albeit very low, which one would expect.
Re: 46-1226 run 122 with squeal - Jim Dutridge - 12-21-2010
Squealing problem has been solved. Thanks to a post on this radio over on ARF, I found that the output transformer had been replaced at some point and they had reversed the primary leads. This led to the radio having positive feedback instead of negative. What actually clued us in was by grounding the bottom side of the volume control the squealing stopped. Removing the ground with the radio powered up brought the squeal back. Reversing the primary leads solved it.
Re: 46-1226 run 122 with squeal - Ron Ramirez - 12-26-2010
That is good news. Thanks for sharing.