Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

37-690 Bass Amplification
#1

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.


Attached Files Image(s)
   

RJ Dial
"Radiodial"
Mendocino, CA
#2

is the switch in proper position?

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#3

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.

RJ Dial
"Radiodial"
Mendocino, CA
#4

on the leftmost knob the Bass is the rightmost position.

https://www.google.com/search?q=philco+3...PyuLnYA_44


zoom on the left knob

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#5

@morzh
Correct. That is the potentiometer that currently does not have any effect on the bass amplification or response.

RJ Dial
"Radiodial"
Mendocino, CA
#6

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.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 49-607 inop
Thanks for the detailed explanation of how this radio works.  The 117z3 tube that was glowing each time I turned it on ...Tennangler — 08:43 AM
41-608 distortion issue
Ah, so you have a code 122 model of the 41-608. I had to do some digging!jrblasde — 10:39 PM
41-608 distortion issue
This set has 7c6 tubes. I will Test both. Thank you. I’ll post the resultphilco4me — 09:45 PM
41-608 distortion issue
You’re welcome! I’m following with a curiosity. I have a 49-906 which had a tube go out on the FM RF circuit, and it cau...jrblasde — 09:20 PM
philco4me
Thank you so much for the fast reply. I will Test that 7c7 and let you know Thanks againphilco4me — 09:17 PM
41-608 distortion issue
To me it definitely sounds like an issue with the 7C7 preamp tube. You’ve pretty well narrowed it down. You might just v...jrblasde — 09:12 PM
41-608 distortion issue
I have Tried several different records with same result. I even played the same records on my 46-1209 and they play fine...philco4me — 09:09 PM
41-608 distortion issue
I was formerly an audio-video system engineer. The “s” sound is a great test to the frequency reproduction of a system. ...jrblasde — 08:55 PM
41-608 distortion issue
Good evening For example s sounds are distorted you cringe when you hear it. It seems to have come on suddenly. Highs a...philco4me — 08:42 PM
41-608 distortion issue
Good evening! Could you elaborate a bit more on the distortion? Is it perhaps static-y sounding, for instance, or is it ...jrblasde — 08:26 PM

[-]
Who's Online
There are currently 405 online users. [Complete List]
» 2 Member(s) | 403 Guest(s)
AvatarAvatar

>