[Phil27]

I don’t know how to test a vintage radio speaker. I have read of a “click test” with a 9 volt battery but I don’t know how to do it. I have Stromberg Carlson 62 speaker that I want to test. I have no idea as to where to place a 9 volt battery to do the test. Also I’m unsure as to where to place my multimeter probes when testing a speaker or what the approximate ohm readings should be, to indicate it’s good, if I test using my multimeter. 

I recently started up this hobby and I realize for all you folks this is elementary but with no electronics background, no vintage radio clubs to join or attend because of Covid, my education has been limited to youtube videos or forums like this one. I have read some of the old radio instruction books but back in the ‘30’s when they were written there were no 9 volt batteries or modern digital multimeters.

Any assistance would be greatly appreciated.

[RodB]

Hi Phil,

Looks like you have an electro dynamic speaker. This is a speaker that has a coil of wire that connects to the radio's power supply to create the magnetic field, generally known as the field coil. Modern speakers use a permanent magnet. The field coil is the big coil on the back of the speaker. The device on the side of the frame is the output transformer which sends the audio signal to the voice coil that moves the cone and creates sound. You can use the multimeter to check the field coil which should measure several hundred up to 2000 ohms. The other 2 pins are the transformer primary and should measure several hundred ohms. You can try using a pair of test leads connected to the primary and momentarily connect a battery and you should hear clicks from the speaker. If no clicks then connect your 9 volt battery to the field coil. Then try momentarily connecting another battery on the primary.

[RodB]

Continuation: So when you get this far and still no clicks then double check your connections. All you want to do is send pulses into the transformer primary and get clicks from the speaker. I noticed that the transformer is a push pull which means the primary has a center tap. You can send pulses across any pair of primary wires. When you test the primary with your multimeter be sure to test both halves. They should measure close to the same resistance.

If you don't get clicks then one or more of the coils is bad, including the transformer secondary or the speaker voice coil. Let us know how it goes.

[Chas]

If the fingers/hands are used to hold the bare ends of both the battery and speaker coil, (field or the primary of the output transformer) wires there is a possibility doing the "click" test, that, a good coil can induce a high voltage pulse and give an electric shock. As unpleasant as that is, the shock, in of itself, indicates the coil under test is good.

Many Digital Volt Meters having the ohms function, have a problem giving correct resistance values of an inductor like an output transformer or a field coil. It is best to use an analog ohmmeter for these large inductor resistance measurements.

[OZ4]

This may be a dumb question but do you have the rest of the radio?

[Phil27]

I did get a small shock when connecting the 9 volt to the two wires coming from the field coil but no click from the speaker. The resistance there was measured at 1.05 K.

I’m confused as to what you mean when you mention the two pins to test the primary transformer. I measured between points from 1-2, 1-3, 1-4, 2-3 etc on the photo and the most I got from any combination was 2.0 ohms. I’m not sure where the two pins I should be measuring from are.

The speaker is not connected to the chassis at this time, should it be?
Thanks for your patience.

[Phil27]

Yes I do have the whole radio, Stromberg Carlson 62, and will have further electrical questions later on but for now I was just trying to establish what works on this radio or how to test to see if it’s working. I haven’t fired it up yet because it was previously worked on and I’m trying to figure out the electrolytics and replace them before turning it on.

I started this hobby because I like working with wood, I wish I had taken a before photo because it was in rough shape, but the cabinet turned out ok.

I wish I had a better electronics background but I don’t which is why I depend on advice from experts at this forum.

[RodB]

Nice job on the cabinet.

You are getting somewhere with the measurements. The field coil should measure around 1000 ohms. Follow the wires from the coil to the connector and measure the coil. If you have a printed copy of the schematic you can note the terminal numbers of the speaker field on the diagram. The remaining terminals will connect to the output transformer.