Magnavox Telemegaphone Speaker - Printable Version
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+--- Thread: Magnavox Telemegaphone Speaker (/showthread.php?tid=19389)
Magnavox Telemegaphone Speaker - mikethedruid - 12-20-2018
I have finished working on my Philco Socket Power. I intend to use it for the B supplies to my Freed Eismann Model 50. Now I am working on a Magnavox Telemegaphone speaker to use with it. When I first checked it out it didn't seem to work at all, but, after taking it all apart, I found that both the voice coil and the magnetic field coil were reading approximately right after stripping back a little off the wires that go to them They each read 8 ohms. The speaker transformer reads correctly too. Must have just been corrosion between the old connectors that were screwed to the binding posts and the posts themselves. I knew right away what the voice coil wires were as soon as I saw them connected to the transformer. When I disconnected them from the transformer and very briefly touched them to a 1 1/2V AAA cell I could hear a feint crackle. Then I wondered if the other wires were to excite the magnetic field of the speaker, so I connected another 1 1/2V cell across them, and again briefly touched the wires to the field coil to another battery. The sound was much louder, so I knew they must go to the field coil, it is also 8 ohms. I looked online, and that is what it is supposed to be. If anyone here has more information on this kind of speaker, PLEASE let me know. I would like to know what the correct voltage is that I should be using for the field coil on this speaker. I am sure that 1 1/2 volts will allow me to listen to the radio, but I would like to get the full amount of sound from it that this speaker can produce. Thanks.
RE: Magnavox Telemegaphone Speaker - Chas - 12-21-2018
The Magnavox pot coil field is 6 volts 1 amp DC. Must be DC with no ripple or the ripple will become noise in the sound... The output transformer (attached) is intended to be the plate load suitable for most battery set output triodes, 01a, 112, 71a. IMHO not more than 20ma.. There should be a full coverage information label pasted on the bottom, usually, it has worn off..
GL
Chas
RE: Magnavox Telemegaphone Speaker - mikethedruid - 12-21-2018
Thank you very much for this information, Chas ! It will be very helpful. Mine still had a badly worn label on the bottom, but I had to remove it to get continuity with thew wiring again. The connectors had lost continuity with the binding posts through electrolytic action from the field coil side. I had to remove the label to get at the screws beneath it that held the binding posts and wires to them. Sad. If you ar anyone else has a picture of the label, please post it, and I will scan it and glue it back on the bottom once I finish restoring the speaker. Right now I have to bump out some dents in the field coil cover. I removed it easily enough, it is held in place by a big brass or bronze snap ring.