10-13-2017, 02:02 AM
Hi, everyone:
I have an early Model 70 (non-AVC, brass escutcheon) I'm working on, and I just spotted a new-ish 5.6 Megohm resistor hiding behind and shunting the 500pF capacitor (#28 in Bulletin 57) from the 2nd detector (24A) plate to ground. It looks like it was added some time in the 1950s or '60s, because it's the brown smooth cylinder shaped carbon resistor common in those days, though it's a 5%er so it could have been later when those were cheaper.
Basically, it goes from the plate of the 24A to ground, in parallel with the .0005 uF capacitor (28).
Wanting to keep the set as original as possible, I'm inclined to remove it, but I'd like to know why it was likely installed there. What was the purpose of adding this resistor to the circuit? Is there any reason not to remove it?
I just recapped the radio and it sounds good other than needing an alignment, and I wanted to figure out this resistor before I do that. If I know what it was supposed to fix, maybe I can anticipate what I'll have to expect on removing it, or I'll know I already fixed it with my recap.
I don't mind telling you this is my third, favorite, oldest and most pristine 70 I own, and I can't wait for it to go on display! (It was a deal because it doesn't have the coveted Mershon capacitors, but it does have the original Sprague ones, and I want whichever ones it wore out the factory door!)
Thanks in advance. I tried Googling this, thinking this was a common practice, but any searches containing the words "Philco" and "resistor" come up with volume control discussions.
I have an early Model 70 (non-AVC, brass escutcheon) I'm working on, and I just spotted a new-ish 5.6 Megohm resistor hiding behind and shunting the 500pF capacitor (#28 in Bulletin 57) from the 2nd detector (24A) plate to ground. It looks like it was added some time in the 1950s or '60s, because it's the brown smooth cylinder shaped carbon resistor common in those days, though it's a 5%er so it could have been later when those were cheaper.
Basically, it goes from the plate of the 24A to ground, in parallel with the .0005 uF capacitor (28).
Wanting to keep the set as original as possible, I'm inclined to remove it, but I'd like to know why it was likely installed there. What was the purpose of adding this resistor to the circuit? Is there any reason not to remove it?
I just recapped the radio and it sounds good other than needing an alignment, and I wanted to figure out this resistor before I do that. If I know what it was supposed to fix, maybe I can anticipate what I'll have to expect on removing it, or I'll know I already fixed it with my recap.
I don't mind telling you this is my third, favorite, oldest and most pristine 70 I own, and I can't wait for it to go on display! (It was a deal because it doesn't have the coveted Mershon capacitors, but it does have the original Sprague ones, and I want whichever ones it wore out the factory door!)
Thanks in advance. I tried Googling this, thinking this was a common practice, but any searches containing the words "Philco" and "resistor" come up with volume control discussions.
"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!
