The PHILCO Phorum
Zenith K526 - Printable Version

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Zenith K526 - Justin A - 09-21-2023

OH MY you guys are amazing! What a history lesson, my grandson and I really enjoyed the detail of rural life and the radio, which is how they learned of outside news, and commodities for the farms.

I keep staring at my project and wonder wear to start! I like the idea of building power supplies but it would be cool to keep it all stock, I just don't know how practical that would be....

I still have one on the bench to complete. Its the Zenith K526 and just got all he caps in the mail last week. I am such a Newby! Some on this stuff I have not thought about since I was 14. Now 71, I have that same amounts of time I had then. I just have to rotate my time around honey dues etc.

I have a question about replacing the electrolytic cap in the Zenith. I purchased single capacitors to replace the one electrolytic. It has four (4) lugs. I for the life of me cant figure out where the other end of the new cap goes and where it gets landed! I lift the components from the original position and pay attention to polarity, but what the heck! Where does the other end go! To chassis ground? Don't laugh, I took my last electronics class in 1970. I should break out my Amateur Radio Handbook, I bet the answer is there I am sure!

justin-

Zenith K526 - Radioroslyn - 09-21-2023

Zenith Radio Corp.: K526W (nostalgiaair.org)

If you look right above the symbol for each cap you'll see a shape. It's noted on the cap next to the terminal and on schematic.
C10A is a triangle, '10b is a square, '10c is blank, and '10d is a half round.

RE: Model 37-38B - Justin A - 09-21-2023

Terry,
Nubi here! I don't want to be "one of those guys"
Thank you for sharing the schematic but it just leads to another stupid question. Although, I did see the symbols on the electrolytic and I think I get that part, thank you for the reinforcement.

Why is my Photofact Folder schematic dated 1953 for the Zenith K526 differing?

Then again it "clearly shows the connections" for the electrolytic clearly, but one value is differing? My drawing shows: and the cardboard can electrolytic cap has these printed on it as well.....
C1A at 80 mfd at 150 vdc
C1B 40 150
C1C 40 150
C1D 40 25

The one that you graciously sent me:
C1A 40 150
C1B 40 150
C1C 40 25
C1D 80 150

differing vintage?

regards, justin-

RE: Model 37-38B - Radioroslyn - 09-22-2023

Oh no it's one of "those guys" lets  RUUUUUUNNNNNN![Image: https://philcoradio.com/phorum/images/smilies/icon_lol.gif].

Here's the scoop, the schematic I linked to my post is from Radio Riders. They span from 1923-1954, are free, and are direct copies from the manufacture's service info. Here's a link to find a schematic: http://www.nostalgiaair.org/Resources/

Sam's photofacts cover from 1946- into the 2000's, have to buy them unless you know someone[Image: https://philcoradio.com/phorum/images/smilies/icon_twisted.gif]. The biggest difference is that they are redrawn from the originals and parts are renumbered. They also have listed some equivalent replacement parts which can be handy sometimes.

There's also Beitman's Most often need schematics 1926-1969  https://worldradiohistory.com/Beitman-Manual.htm Or if you just like reading https://worldradiohistory.com/ has tons of radio magazines from the teens-'80s.             

Enjoy!

RE: Zenith K526 - David - 09-22-2023

Link to a post in the past with info about couplates   https://philcoradio.com/phorum/showthread.php?tid=12188&pid=174466#pid174466

RE: Zenith K526 - MrFixr55 - 09-22-2023

Hi Justin,

In the case of your 4 separate electrolytic caps, all negative terminals connect to "B-". This is not necessarily Chassis Ground, but it is the "Common Negative" for the B supply of the radio. The chassis connects to this common negative through a capacitor and sometimes through a 150K resistor. This is to allow AF and RF energy (the metal chassis, the tuning cap stator, IF transformer case and tube shields) to connect to B- without allowing a lethal amount of electricity to pass through a person contacting the chassis. If your original 4 section filter "cap" (capacitor) was a metal can, you will find that it was mounted to the chassis through a bakelite insulator and secured to that insulator by 4 twisted tabs on the outer diameter that extend to and are electrically connected to the metal can. The can also likely serves as the B- "Mecca Point" where all of the B- connections (1st Audio, IF and convertor cathodes, the output tube cathode bias resistor, etc.) and Detector / 1st Audio filament return connections are made.

Looking at the Schematic, an 80 uF 150 WV (Working Voltage) cap connects between the B- Mecca and the junction between the output transformer red wire and R18, a 22 Ohm resistor. This replaces the "Half Moon symbol" connection to the old can cap. A 40 uF 150WV cap (replacing the square symbol) connects between B- Mecca and the junction of R16 and R17. (The other end of R17 connects to the brown lead of the AF Output transformer (This serves the same purpose as the "hum bucking" coil on the older electrodynamic speakers on pre-war radios.) Another 40 uF 150WV cap (replaces the triangle symbol) connects between B- Mecca and the junction of R16 and the 99V B+ to the output tube screen and the IF transformer primaries.

The final capacitor, the 40uF 25v cap connects between B- Mecca and the junction between the output tube cathode and the output tube's cathode bias resistor, R13, and serves as a "bypass" cap, adding stability to the output stage. The working voltage of this cap is much lower than the various B+ filters because the voltage drop across the resistor is only about 12V or less. Be careful not to accidentally substitute this cap for one of the others. It will go off like a firecracker (been there, done that).

Be sure not to use the positive terminals of the old cap as terminals for the positive terminals of the new cap ("bridging" the original cap with the new caps") unless you hollow out the original cap and "stuff" it with the new caps. Purists do this to maintain the look of originality and also when there is no room under the chassis to add the new caps. Experts on this Phorum have written articles on "stuffing" cans. If ytu have the room under the chassis for the new caps, add a terminal strip and move the wires from the various + terminals to the original caps to the terminal strip and connect the corresponding + connections for the new caps to these terminals. In some cases, the connection for the + terminal can be made to a "junction" point.

Another important component to replace is the selenium rectifier. These tend to suddenly fail catastrophically and create a rotten egg stench.

RE: Zenith K526 - Radioroslyn - 09-23-2023

There's one other pair of wires on the opt the yellow and green ones. These form a negative back circuit (sometimes called a loop) in the audio to boost the low frequencies at low volume levels. This one is kind of an odd way to do it as most won't have a separate winding on the opt for it. It's more common to see a tap in the opt 2dy or cap & resistor from the plate of the output tube back to the preamp stages. Or to a tap in the volume control.

A lot going on in that little puppy...

GL

RE: Zenith K526 - morzh - 09-23-2023

The fun part.


I have to compare the pain of figuring out and then replacing (without even restuffing) the lytic capacitors to the pain of me learning how to create parts in Altium designer CAD.
Not sure which one is more painful. I think the latter but I believe people who say the former is bad.

On the technical side, all that had to be said has been said, so I have nothing to add.