Electrolytic question on a 40-180. - Printable Version
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Electrolytic question on a 40-180. - Joemwerth - 02-28-2021
(thread title edited by admin to show correct model number)
Hi folks.
My question relates to the metal can 12 uf electrolytic cap that is isolated from the chassis, part # 30-2405. There are two wires that protrude from this capacitor. A tan wire which comes from the 41 rectifier tube cathode pin and which I’ve connected to the “+” side of my new electrolytic capacitor. I’ve connected the “-“ side of my new electrolytic cap to the floating ground connection. Question: To where does the black wire connect that comes from a two tab terminal strip near the audio power tubes? It used to go into the old metal capacitor. Does it go to chassis ground...or to the floating ground connection? When I connected it to the floating ground, the rectifier tube would arc a few seconds after the filaments light. Thanks for your help.
RE: Electrolytic question on a 40-280. - Radioroslyn - 03-01-2021
Hi and welcome to the Phorum,
Methinks you have the wrong model number listed for your set. I think it's a 40-180. Looks like you have a couple of choices. #60, 54, and 49. I'm betting on 60.
Obtw the 41 tube is one of the audio output tubes, there are two of them. The 84 tube is the rectifier.
https://philcoradio.com/library/download/service%20info/yearbooks/1940/split/Part52-Philco%201940%20RMS%20Year%20Book.pdf
RE: Electrolytic question on a 40-280. - Joemwerth - 03-01-2021
Terry.
My bad. Yes, the model is 40-180. And it has the 84 rectifier tube. Sorry about that . Thanks for any help!
Joe
RE: Electrolytic question on a 40-280. - RodB - 03-01-2021
+1 for Terry. The negative side of the electrolytic goes to three resistors, two 470k and a 150 ohm, probably all tied to the terminal. They provide negative bias to the 41 tubes.
RE: Electrolytic question on a 40-180. - Joemwerth - 03-01-2021
Thank you gentlemen for your kind and helpful replies. Where I was confused was that particular capacitor is isolated and had a floating ground. I wasn't sure how critical that is vs. a direct chasis ground. Also, the schematic doesn't really make the distinction between the floating ground components vs chasis ground. Thanks again guys!
Joe
RE: Electrolytic question on a 40-280. - Radioroslyn - 03-01-2021
<Also, the schematic doesn't really make the distinction between the floating ground components vs chassis ground.>
It does there's no ground symbol.
The circuit before mentioned isn't really floating it's just grounded (@#59) thru 165 ohms worth of resistors. It subtracts some B+ thru these resistors and makes negative voltage. This negative voltage in turn is used to bias the grids of the 41's the output stage, the 7C6 grid in the 1st audio stage, and the 1232 suppressor grid in the rf amplifier. These grids need to be at a negative voltage to help mange the electron flow within the tube. In most cases without this negative bias too many electrons will flow from the cathode to the plate causing excessive current and can damage the tube or parts connected to it. Things like output transformers, chokes, field coils, and resistor can be at risk.
Point is that some folks think that the negative side of a filter capacitor always is connected to the chassis. Not so much!
Now the post war ac/dc sets those have a floating B- but that a different story for another day....
RE: Electrolytic question on a 40-280. - Joemwerth - 03-01-2021
Thanks Terry for the excellent explanation! I understand now. Appreciate your time
RE: Electrolytic question on a 40-280. - unclevinny86 - 03-01-2021
The 40-180 I’m working on is exactly as Terry stated. The 12 mfd on my set has red and brown leads. Red goes to the 84 tube and brown is tied to single post terminal strip with connections to the 41 tubes through 470K ohm resistors as noted as well as the 150 ohm and 15 ohm resistors. There’s a connection between the 150 and 15 connecting to the 7C6 and the 1232 as noted. The 16 mfd connects to chassis.
Just curious, are you restuffing the old cans or just snipping and putting the new electrolytics under the chassis? I’m going to add a terminal strip for both mine and just disconnect the old. One strip will tie to chassis ground with the one for the 12 mfd not grounded to chassis.
RE: Electrolytic question on a 40-180. - Joemwerth - 03-02-2021
Hi Vinny-
Like you, I’ll just snip the old caps, install terminal strips and install the new electrolytics.... same plan as you. Now, just need to find a little time to get back at it!! ?
RE: Electrolytic question on a 40-180. - unclevinny86 - 03-02-2021
I hear you! This is my after I finish my workday project, just taking my time. Been focused on cleaning this past week and got the loop assembly and SW loop rewired. Got chassis cleaned up pretty well Sunday and working on rust removal now. Using Metal Rescue and so far am very pleased with the results!