37-690 Bass Amplification - 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: 37-690 Bass Amplification (/showthread.php?tid=25435)
+- 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: 37-690 Bass Amplification (/showthread.php?tid=25435)
37-690 Bass Amplification - Radiodial - 12-07-2024
I have no Bass amplification on the 37-690 I'm trying to finish up.
All caps and resistors have been replaced
Known good 6K7G and 6J5G in place.
All the wiring around the 2 Bass Amp tubes have been checked and cross checked against the schematic.
That leaves signal tracing to find where the audio is failing. This thing should act like a basic amplifier circuit I suppose.
I injected AF onto the wiper of the bass control (120). That worked OK.
I then injected the signal onto the grid cap of the 1st Bass amp 6K7G. A decent pop, but no audio. That's where I lose the possible signal injection path.
Any tips on where to apply the audio signal to troubleshoot the Bass Amp section (lower right corner of the schematic)? Everything else in the radio works now.
RE: 37-690 Bass Amplification - morzh - 12-07-2024
is the switch in proper position?
RE: 37-690 Bass Amplification - Radiodial - 12-07-2024
Oh, I'm way beyond the basics here, I'm 13 weeks into this thing. I imagine you are referring to the band switch. Yes all is correct with it, as bass amplification only works on the AM band.
RE: 37-690 Bass Amplification - morzh - 12-07-2024
on the leftmost knob the Bass is the rightmost position.
https://www.google.com/search?q=philco+38-690+front+panel&oq=philco+38-690+fron&gs_lcrp=EgZjaHJvbWUqBwgCECEYoAEyBggAEEUYOTIHCAEQIRigATIHCAIQIRigATIHCAMQIRigATIHCAQQIRigATIHCAUQIRigATIHCAYQIRiPAjIHCAcQIRiPAtIBCTE3MDMwajBqOagCDrACAQ&client=ms-android-verizon-us-rvc3&sourceid=chrome-mobile&ie=UTF-8#vhid=F0xNQNEjoHAqXM&vssid=_LN1UZ6DHIqCZptQPyuLnYA_44
zoom on the left knob
RE: 37-690 Bass Amplification - Radiodial - 12-08-2024
@morzh
Correct. That is the potentiometer that currently does not have any effect on the bass amplification or response.
RE: 37-690 Bass Amplification - morzh - 12-08-2024
Honestly, I do not remember mine having that much of an effect either. I remember looking into it, and then I was not able to make it very noticeable.