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38-116 Bass? - Printable Version

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38-116 Bass? - madsowry - 03-11-2022

Hi All,  I'm testing my 38-116 after complete replacement of all paper caps, and most of the resistors that were out of tolerance.  This thing was a mess as far as the chassis was concerned.  It was shipped with chassis in it.  Needless to say when I got it 4 of the 5 shafts were snapped off and the back of the chassis was bent up with the input trans. bent too.  So I welded 2 of the shafts, made one from scratch and mechanically made the other one work with a butt connector and a few alterations to the bracket.
  At any rate it works and works very well.  The plate voltage is a little low on the output tubes but it still plays well and loud if wanted.  My main question is with such a nice big speaker I would think the bass output would be very noticeable but mine is negligible.  The 3 position switch on the power switch does not seem to do anything.  I can get a little more lower tone by using the treble and sensitivity pot(which was a lot of fun tearing apart to fix the shaft).  But the bass on the power switch does nothing.  Is there something I can do different or replace to get some bass.  That shaft was broken also but I took it apart and was able to braze it back together and cut in a groove for the C or E clip and it works well except for no bass.
  Any suggestions or help would be greatly appreciated!!
  Dick

RE: 38-116 Bass? - Radioroslyn - 03-11-2022

So are the contacts clean and in alignment and move when you rotate the shaft? Look for broken parts cracks, loose leads on the mica caps near the tone switch. Might have been damaged but not that noticeable. I would have a look at the volume control, to see if the resistance at the tap is ok. If it's open that's a problem.

There's a start.

RE: 38-116 Bass? - madsowry - 03-11-2022

Thank you, Terry I took the switch back apart and made sure the contacts were clean and lined up which you really can't mess that up because of the placement of the little tabs that you bend over to hold the switch together.  Don't really want to take it apart again cause the little tabs look a little stressed.  I checked the resistance of the volume control which is actually 2.2M and the tap was right at 1M.  As far as mica caps, I don't see any in the area or in the circuit that would cause this but I definitely can be wrong about that.  I thank you again and if you have any more ideas I'm all eyes and ears.
Thanks
Dick

RE: 38-116 Bass? - Ron Ramirez - 03-11-2022

There are two resistors and two capacitors to check in the bass control circuit. The parts are the same, but the part numbers differ between Code 121 and Code 125.

70K resistor - part (103), code 121 - part (89), code 125
2 meg resistor - part (104), code 121 - part (95), code 125
Two .008 uF capacitors - parts (105) & (106), code 121 - parts (91) & (92), code 125

Make sure these are properly connected. Make sure the bass tone switch is actually functioning as designed. The wiper arm of the bass tone switch should be connected to chassis ground.

RE: 38-116 Bass? - madsowry - 03-12-2022

Thank you Ron
   Yeah mine is a code 125 and the parts are correct and in good shape.  The resistors are both good and within spec. and the caps have been replaced with new.  You did make me think about the ground more because this one has a piece of fish paper or cardboard in front of the  switch housing.  I think when I installed the switch this paper was not centered around the threaded part so it wasn't making a good ground.  I reinstalled it making sure to get good contact to the chassis with the switch shaft housing and I can tell the difference when switching through the 2 bass contacts.  
   I'm wondering if there is a way to get more bass?   Could I put more capacitance across the second cap in the bass circuit and get more bass in that position?  Maybe I'm rushing things and once I get this thing in the cabinet with the clarifiers the bass will increase, I don't know?
Thanks again

 Dick

RE: 38-116 Bass? - Mondial - 03-12-2022

Are you playing the radio with the speaker out of the cabinet? That would explain the lack of base.

RE: 38-116 Bass? - madsowry - 03-12-2022

Thanks Mondial Yes I am testing it while out of the cabinet. The cabinet still needs to be refinished and I'm recuperating from hip replacement surgery so it will be awhile before I get to the refinish job. Yeah, I kind of thought that being out of the cabinet would make a difference so I'll wait and get it all put back together and see how the bass is then.
Thanks again
Dick