Packard Forum Index » Pre-War (1899-1942)

Looking at some offsite blogs about electromagnetic speaker coils, this tidbit might help:

The field is 1125 ohms. You could use a 1,000 ohm 10 watt resistor in place of the field. Might have to increase filter cap value to eliminate hum.

As for it having 6v DC, I guess it depends on what it does. If an electromagnet, it would need a build-up and drop of voltage to be able to generate a magnetic field but perhaps there is also a regular magnet and voice coil within it that can somehow cause the fluctuations needed. Otherwise an electromagnet simply won't work with pure DC.

There is a voice coil coming off the ouput tube and audio transformer. It is shown on the schematic just above the field coil. The electromagnet sets up a strong field and works just as the permanent magnet fields work on modern speakers. I just remember reading in an old radio book that in order to cut costs or reduce components some radio mfgs would dual purpose items when possible and it went on to mention how speaker field coils were a prime example of a dual purpose component.

I have to examine the schematic but there will be no electromagnetic field generated strong or otherwise on DC except for the moment power is first applied and even then it's only for an instant. That's just physics. Transformers won't work with pure DC either which is why there is a vibrator and an electromagnetic coil is simply half of a transformer (one coil rather than one input and one output). Of course, I'm thinking in terms of a transformer which induces a current across an iron core so it might be different when there is a permanent magnet involved.

I am aware nothing field wise happens instantly but it only takes a few milliseconds for a field to generate. With a tube radio it does not matter because unlike transistors nothing is happening until the tubes warm up anyway and by the time transistors came along small strong permanent magnets had taken over for most electromagnet field coils. I was surprised to see large electromagnet speakers are still made and available for some high end audio equipment. Wonder what the sound advantage of the electromagnet might be over a permanent magnet. I know audio aficionados think a tube amplifier has a warmer sound than solid state but not sure why the speaker would be that different to warrant the cost and added circuit complexity.