[Rob Quay]

Hi Guys- I’d like to know something about these capacitors. Are either of them electrolytic? The older one has a 1924 date on the label. After replacing 4 of them in a kit built 1920s radio I’m getting reception but also a loud hum indicative of bad filter caps. Thoughts on either cap? Thanks. - Rob Q.

[morzh]

On the left seems to be electrolytic; on the right is probably a paper one.

[Rob Quay]

Thanks. That’s what I was thinking. Another question for the Phorum is- “When did electrolytic caps come into general use?”.  ……….always one more question.

[Mondial]

Electrolytic filter caps began appearing commercially in radios in the late 1920's. The first instance I am aware of was in a Crosley Bandbox from 1928. It had a large cylindrical cap labeled  "Mershon Condenser". It was a triple section liquid filled wet electrolytic.

Commonly, elecrolytics appeared more frequently in radios around 1931 or so, replacing the large paper filter cans.

I believe both of the caps in your photo are paper. The cylindrical one appears to be a hermetically sealed oil filled cap, given the capacitance is only .47 uF, and is a lot newer than the other.

What are you using for the power supply of your 1920's radio? These sets were designed to run on batteries for both the filament and B+ supplies. Is it a later set with a built in supply or battery eliminator?

[Ron Ramirez]

The first Philco home radio to use an electrolytic was model 21 from early 1931. It used one very large Mershon, which was either 14, 16, or 18 uF, depending on who you believe. Even the (scant) Philco documentation available disagrees on the actual value of that Mershon. It was used as the input filter; the other filter capacitors were paper and enclosed in a large rectangular metal can mounted under the chassis.

Models 70 and 90, which came out months later, used two 6 uF electrolytics, either Mershon (copper) or Sprague (nickle plated).

[Rob Quay]

Thanks for the information. I’m surprised at how quickly the radio industry evolved in the twenties and thirties. From crystal radios to multi tube marvels! 
I’m guessing that the radio I mentioned is from the late 20s. It has a multi tapped transformer and rectifier tube. Someone put it out for the garbage and it ended up at my house. - Rob

[morzh]

Well, the radio hints that neither of them is electrolytic.

And yes, as Ron had noticed, 0.47uF is not a value for an electrolytic of this size anyway.

[Chas]

Knowing the make/model of the radio will go a long way in locating a schematic and identifying any hum problem...

Chas

[Ron Ramirez]

That is a nice looking radio. I wonder why anyone would want to throw it out? Good save!

[morzh]

Ron


Perhaps Snoop Dogg or Ice T did not sound quite nice while listening to them on this radio......

[Ron Ramirez]

Mike - Good point...

[Rob Quay]

Hi Guys,
Thanks for the information. The radio was a mess when I got it. My wife did the cabinet restoration. 
I’m assuming that the radio is a kit given the number of holes that were drilled and then redone. The escutcheon says Shelby but doesn’t match anything I’ve seen from them. There’s no other identification. The back of the cabinet had to be routed out before the rectifier tube would fit properly so I’m wondering if the radio was even finished. It’s quite heavy- about 50 lbs.
Further investigation shows that the radio only works with the plug in one way and then with the ground connected. Not good. Without a schematic I’m at a loss here. Thoughts?
I know I’ve wandered into the repair area of the Phorum without intending to so I apologize for that! Thanks again. - Rob Q.

[Mondial]

Rob, why don't you post some photos of the chassis and power supply. The set may have been built up from bits and pieces of different radios, some of which may be recognizable. 1920's radios are all pretty much alike in their basic circuitry.

Are you saying that the radio does not power up at all unless you connect an external ground? If so then something is definitely miswired in the AC line power supply wiring.

[Rob Quay]

Here are the pictures. I kept the parts that were taken out so that the radio can be put back as found if desired.                         

[morzh]

Let's just say that I would not plug this radio in without thoroughly familiarizing myself with what it is and whether the repairs are valid.

Also if it is a transformer radio, it would bother me if it only worked with the plug one way.

The most benign guess is, they are using a "Line" as an antenna, same way they do in 86 Philco. Then plugging it in reverse connects the Antenna to the "Neutral" which is a GND.

But still, should be looked at.