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Philco 42-345 12 mfd cap - Printable Version

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Philco 42-345 12 mfd cap - bridkarl - 05-23-2024

The cap in there had a silver end and a paper end with only negative signs on the case so I have no idea if this was installed correctly. I may not be understanding the antique cap symbol here. Was there some convention here with the negative signs on the case?


I read that symbol as the bar being positive and the three sided square as negative. Judging from 40 A. So I’ll read the metal end of the cap as negative.

So the positive end of the cap goes the connection to the field coil. The yellow wire in the foreground runs up to the speaker coil.

The negative end goes to the termination of the 470k resistor with the yellow green wire.

RE: Philco 42-345 12 mfd cap - morzh - 05-23-2024

Is there a question?

RE: Philco 42-345 12 mfd cap - bridkarl - 05-23-2024

Am I interpreting the three sides of the symbol as ground correctly?

RE: Philco 42-345 12 mfd cap - morzh - 05-23-2024

I never paid attenton to that, but instead what would resolve your question much faster would be you posting a photo of both the symbols and both ends of the cap.

Meantime, I can tell you that the case on the caps is always the Negative.

Caps - bridkarl - 05-23-2024

This thing looked almost homemade which is why I didn’t post any pics. I wasn’t sure they would be any use but…two dark lines and what appears to be “Richard Hopkins” stamped on the case. 

You’re quite correct so I’ll be sure and be more clear in the future.

RE: Philco 42-345 12 mfd cap - morzh - 05-23-2024

Well, I am not familiar with the bars' fucntion, but what they are certainly not is being the polarity indicators.
Possibly, just a format of putting the whole pattern/marking on the cartridge.

Now, you aluminum side is the minus, and your phenolic (or is it some cardboard) side is the plus.

RE: Philco 42-345 12 mfd cap - bridkarl - 05-23-2024

Thanks. I’m just trying to be careful with all this.

RE: Philco 42-345 12 mfd cap - morzh - 05-23-2024

Just to clarify.

The symbol for the cap is the bucket and the bar inside it.
The bucket is the case is the Minus.
Goes to the centertap of the power xfmr.

The bar is the center electrode is the Plus. Goes to the Field Coil and the Cathode of the Rectifier tube.

bridkarl - bridkarl - 05-24-2024

Thanks. That seems to clear up my confusion. This is interesting as I’ve never seen one of these 7Y4 loctal rectifier tubes before. 

Apparently if I understand this right it’s using the center pin as a ground connection between that point and the Bakelite block where it hooks up to the .01/.01 caps on pin 1. 

Have to say it threw me when I first looked at this - counted all the pins and saw the black wire soldered to the center pin. It should be visible on the picture right below the red wire.

Until I looked at the tube data sheet and realized the pin connected to the shell I thought it had been miswired.  As I may have said I’m the second person to have recapped this so I’m trying to check and make sure nothing was done amiss.

RE: Philco 42-345 12 mfd cap - morzh - 05-24-2024

>>>it’s using the center pin as a ground connection between that point and the Bakelite block where it hooks up to the .01/.01 caps on pin 1.

No, no, no. No one said "Ground".
The center tap is THE MOST NEGATIVE point of the whole radio. If you are talking of the 12uF cap, the cap #57 that is, this is the only cap that is connected to it.
Also connected to it are: the divider's Resistor # 59 and the Grid Bias resistor #51.

The GND is the other divider's resistor #58 and the 4uF (#40A) cap's Negative; this is where the .01/.01 caps GND connection goes, if we are talking of the AC input filter #61.


Again, GND and the Centertap are NOT the samel

bridkarl - bridkarl - 05-24-2024

I saw the same ground symbol in two different places which I assumed meant they were the same.  Thanks for clarifying this.


I replaced the black wire here from point 1 of the block to the center tap as I found it. 

I obviously need to shut up and study this some more as it appears I don’t know what I’m looking at.

RE: Philco 42-345 12 mfd cap - RodB - 05-24-2024

Generally, when we use the term center tap it refers to a tap of a coil usually at the electrical center of a transformer secondary. Are you referring to the ground connection of the power line filter caps (61)?

RE: Philco 42-345 12 mfd cap - bridkarl - 05-24-2024

I was only referring to the black wire that goes from pin 1 of the Bakelite block to the center pin of the rectifier - which I referred to as the ground. As in the photo.

As I’m reading the schematic this completes the circuit for the pilot bulbs (55) - using a tap off the transformer 60 which - although unlabeled - appears to provide 6.3VAC

But as I said I’m fairly sure I don’t understand what I’m looking at so rather than continue to post uniformed comments I need to go quietly study this. This has been worked on before so I’m just trying to make sure the previous owner didn’t introduce any errors - hence my concern that the wire described above is going what I think it is - providing a ground connection at the pin to complete that 6.3VAC circuit.

RE: Philco 42-345 12 mfd cap - RodB - 05-25-2024

Ah, now it's clear. Yes, the ground terminal of the bakelite block is providing a ground for the tube sockets. Notice the center post of each socket is connected with a bare wire. This makes it convenient to connect tube pins to gnd without having to heat up the chassis with a soldering iron. Important note is to be sure the bolt in the bakelite block is very secure and has a star washer against the chassis. Schematics can be subtle; look at the transformer secondary providing 6.3v to the 7Y4 and pilot lamps. The 6.3v feed runs to the right and disappears into an arrow. This arrow connects to each arrow of the tube filaments and the other side of each filament is attached to ground (maybe the center post?). Full circle!

bridkarl - bridkarl - 05-26-2024

That’s what I thought but good to have the confirmation. Thanks. 

In the process I think I’ve found an error in the schematic parts listing. In the unit I found a .003 mfd/1000 volt cap installed going to the tone control.It was a Philco branded wax cap so I think original.  Part 49 - which is listed in the parts list as 100 volts-  This makes no sense - I’ll assume it’s an error and put in a 1000 volt unit, but I mention this for the benefit of anyone looking at doing one of these.