[Greg]

Hmm... I just noticed that on mine the spring pulling the bottom coil towards the top coil rubs against the bottom coil. That can't be good. Looks like some of the wax is off the bottom coil at that point the spring contacts it.

[dconant]

Looks like maybe both are. It will eventually cut into the coil. Can you move the bottom of the spring out a little on that post? Wonder if I should open mine up and have a look. I was thinking of not opening mine up but just put shrink tube over the grid cap wires.

[dconant]

I have found a 2 meg resistor in the chassis that is not on the schematic. There is no 2 meg resistor in the parts list either.  It is between ground and the junction of the 70K resistor(#103) and the .008 cap (#104). It is pretty well hidden under that 9 pin terminal block. Has anyone else seen this?

[462ron]

Hi Dan, it’s been 10 years since I restored my 37-116 but I seem to remember something about a 2 meg resistor being added to reduce or eliminate a loud pop when changing switch positions. I tried going through the Philco Radio Library section for changes or updates but couldn’t find anything!

Ron

[dconant]

Thanks Ron for taking the time.

Dan

[morzh]

Does it eliminate the pop?
I am not sure I've understood how it helps much.

The charging circuit is the parallel of the two lalves of the potentiometer before and after the tap, in series with the 10K resistor, charging to the voltage that is at the tap.
Now you connect 2M resistor to form a Thevenin with that charging circuit, which does not divide it too much as it is 2M vs possibly a 200K (do not know what the pot is and what the tap is at), so Gosh willing, it reduces the voltage by 10% or so.
And switching to the same or close voltage level will still create the same pop.

[462ron]

Mike I don’t remember where exactly the 2 Meg connects to. Possibly C104 and C105 on the 3 position tone switch takes in some DC voltage and when switching, the wiper grounds out one or the other cap. The 2 meg resistor could soften the discharge. A discharge going into the volume control probably makes the pop noise. I don’t have the full schematic handy to see if there’s any path for a DC voltage buildup. Anyway, it’s been years since I saw that change and just remember it had something to do with that popping noise. Not sure now where I even saw it!

Ron

[morzh]

I honestly did not pay attention as it is so very not important. But as long as we are discussing it, and there is a claimed function, I'd like to understand it.
So far I understood the 2M goes from that denoted by red circle point to GND.

[MrFixr55]

Hi DConant,

Sorry, I missed your question regarding 500WV caps in an AC-DC AA5.

Unless the technology changed, the electrolyte had to be exposed to voltage near the designed "WV" (working Voltage), otherwise the cap would not "form" correctly and the capacity would be much lower than the listed value. I can't remember exactly where I learned this, but it may have been either in the 1940s NRI Radio course or in the US Navy "Basic Electronics" Ca 1953.

In some cases, this may not have been mush of an issue as these caps, back in the 30s to the 60s or so were rated +100% / -20%. In other words, a 40 uF cap could have an actual capacity between 32 and 80 uF!

I think that the specs are tighter now.

[dconant]

Thank you MrFixr55. Now I understand why you said what you did.

Dan