10-15-2017, 03:05 PM
The resistor that is the subject of this post was, indeed, NOT responsible for dragging B+ down. (Especially since I'd already removed it and confirmed it was still about 5.6 Megs.)
It was not one, not two, but THREE intermittent 24A's, all National Union (so now I'm prejudiced against NU), such that my single tube substitution didn't really yield much, and I suspected something under the chassis anyway after my recap and volume pot swapout. I knew I was in trouble when setting down my screwdriver caused audio to drop out! (Wait: Did that really happen? Picked it up and set it down again. Yes, it did!)
With its original tubes in, I could tap on anything in or even near the radio to bring on the problem. Flex the cabinet, poke at the dropping resistor, move a wire (any wire)! It turns out, one tube mostly worked, one sometimes worked, and one worked every once in a while, but all made noise if you tapped anything in the room.
It looks like someone just re-tubed the entire radio (as if that's ever a good practice) with all NOS looking NU tubes, and they just developed or already had internal intermittent shorts. I just re-tubed it again from another 70 chassis I had, and started swapping original tubes in one at a time until it got sensitive to taps again. I chose the second detector position to test all of my 24A's one at a time. Yep, THREE of them were bad! I suspect a heater to cathode short, and now I don't even trust the one that seems to be working fine.
I don't know if the 5.6 Meg resistor was intended to help the situation, but it certainly did not!
I'm still puzzled on the theory behind adding a 5.6 Meg resistor to the 2nd detector plate going to ground.
Now that I've gotten my intermittent 24A's out of the way, I'll go finish the restoration and see if anyone remembers any kind of "fix" involving adding a resistor like this.
It was not one, not two, but THREE intermittent 24A's, all National Union (so now I'm prejudiced against NU), such that my single tube substitution didn't really yield much, and I suspected something under the chassis anyway after my recap and volume pot swapout. I knew I was in trouble when setting down my screwdriver caused audio to drop out! (Wait: Did that really happen? Picked it up and set it down again. Yes, it did!)
With its original tubes in, I could tap on anything in or even near the radio to bring on the problem. Flex the cabinet, poke at the dropping resistor, move a wire (any wire)! It turns out, one tube mostly worked, one sometimes worked, and one worked every once in a while, but all made noise if you tapped anything in the room.
It looks like someone just re-tubed the entire radio (as if that's ever a good practice) with all NOS looking NU tubes, and they just developed or already had internal intermittent shorts. I just re-tubed it again from another 70 chassis I had, and started swapping original tubes in one at a time until it got sensitive to taps again. I chose the second detector position to test all of my 24A's one at a time. Yep, THREE of them were bad! I suspect a heater to cathode short, and now I don't even trust the one that seems to be working fine.
I don't know if the 5.6 Meg resistor was intended to help the situation, but it certainly did not!
I'm still puzzled on the theory behind adding a 5.6 Meg resistor to the 2nd detector plate going to ground.
Now that I've gotten my intermittent 24A's out of the way, I'll go finish the restoration and see if anyone remembers any kind of "fix" involving adding a resistor like this.
"Why, the tubes alone are worth more than that!" (Heard at every swap meet. Gets me every time!)
Philcos: 90, 70, 71B, 610, 37-61 40-81, 46-420 Code 121 to name a few.
Plus enough Zeniths, Atwater Kents and others to trip over!
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