OK folks,
Here is my second post. I have learned a lot but I know just enough to get into trouble. I got another model 60. This one is a 1934, (looking at the cabinet) model B. Another $5 yard sale special.
After looking at it I thought this could be a quick fix, everything looked ok and complete except for the capacitors. Both caps had hard white foam coming on the top. The power cord had an initial length splice into, and one of the caps had been maybe removed or loosed at one time. Also there was about 6 feet of copper wire coiled up loose and stowed. (I think this was used as an antenna).
So i removed the caps in order to restuff them with modern caps. the first one was normal (part number 30-2025 A) (what I was used to seeing). Two power wires soldered to one connection and a ground wire fit tightly in between the cardboard that surrounds the bottom of caps that insulates the caps from the bracket that holds them to the chassis.
The second cap (30-2024) has just one power wire BUT there is no visible ground wire. I can see a mark on the inside of the cardboard tube where there was one. Where would this missing ground wire run to?
When Pull the chassis out of the cabinet to replace the power cord I will have proper access to the rest of the radio BUT were should I look? Any help or hints would be greatly appreciated
Neither of the filter caps (46 & 45) are connected to chassis ground. Both should have a little slide in terminal between the can and cardboard tube. This is the minus terminal. B- is 267 ohms above ground.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 03-15-2023, 12:40 PM by Radioroslyn.)
Thanks Terry
That is exactly what i thought. I can see the ground terminal between the can and cardboard on the first can and I can see where it had been on the second can. I knew they would not go to the chassis ground because of the length they went to in order to insulate them by using the cardboard.
Thanks for the pdf, I'll look it over and chase down the missing ground. I tried to do a quick fix with out taking the chassis out since the rest of the radio looked so good.
It looks like the ground for caps 45 and 46, go through a couple of nodes, then they both go to the same ground, that is after a they both go through a couple of resistors (47).
I think I could just tie in the missing ground from cap (45 or 46) to the existing ground wire on cap (45 or 46), as long as i tie in before the resistors (47).
Here's a drawing of the p/s that's a little easier to follow. Perhaps it's just a matter of semantics. I'm calling it b- because it isn't grounded to the chassis (the exterior of the filter can). You are calling ground because unless it's insulated from the chassis it would be grounded.
Not trying to pick a fight or anything but the chassis ground point is found thru #47. It's used to develop the negative voltage applied to the control grids of the 75 tube (-3vdc) and the 42 tube (-21vdc). Without these negative voltages these tube would draw excessive current and generally would be hating life. Over heating the power transformer and stuff like that.
Voltages listed are off the top of my head not to be used as an exact measurement. Oh and btw some Philco sets one of the filters is at chassis ground and the other is at b-. Some have the b- floating just like your set but there is a filter cap from chassis ground + to the hv ct - to filter the - side of the dc output... Check out #75 on this one https://philcoradio.com/library/download...%20165.pdf Better yet get you one. The 16/116 tombstone is the one to have.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 03-16-2023, 09:33 AM by Radioroslyn.)
Attached are some photos of the radio. to me it looks like a model 60B 1934.
I also attached some photos of the cardboard insulators and the bracket that holds the caps, you can see marks on both cardboard insulators where the ground wires go. Or at least where the one existing ground goes and where the other missing ground should go.
I included a photo of the existing wires, with a white paper towel in the background for clarity. They sure didn't give you any extra wire when they built these radios.
last photo is of the schematic with the caps and wire highlighted. What do you think?
I think what you are asking is: "can the negative lead of electrolytic caps 45 and 46 be connected together?" Yes, they can. The exterior of the capacitor cans of 45 & 46 was originally the negative lead, thus the use of the little metal connection lug that was held between the capacitor can and the insulating cardboard sleeve so that wires could be soldered to it. The cardboard sleeve isolates the negative leads from the chassis which is at ground potential ( 0v). The two negative leads from caps 45 & 46 connect to the center tap of the transformer and as Radioroslyn notes are at a negative potential with respect to chassis ground. This is the most negative point in the radio and is commonly labelled as B-.
Hope that helps.
This is a typical power supply for radios of this era. It produces the B+ voltage for the tube plates and screen grids. It also provides a negative voltage for control grid bias in the audio circuits. Consider the casing of the 2 electrolytics to be the negative connection and don't call it ground. When the negative is connected to the chassis you have grounded it. But not in this case. The electrolytic negatives are connected to the center tap of the hv secondary creating a B- which is above ground. Thus, when resistor 47 is connected to B- and chassis ground it creates the negative bias for the audio tube grids. If you ground the electrolytics to the chassis you loose this bias voltage and the audio tubes will experience catastrophic consequences. It's very important to follow the schematic.
...RodB you don't know how many times I've done exactly what you did. Type out an answer only to find after it posts that one or two others beat me to it!
...RodB you don't know how many times I've done exactly what you did. Type out an answer only to find after it posts that one or two others beat me to it!
