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Vintage 1940s Hushatone Speaker

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Humanoid:
Someone gave me an old speaker from the 40s: Hushatone Pillow Speaker model BE-301. Unfortunately, the TS connector is gone and it came with no manual and I haven't been able to locate a manual online.

I tested the ohms of it and it seems to register 23 M ohms, which doesn't seem right. So I don't know if it's messed up inside or I'm reading it wrong.

I found one Ebay posting where it said it was 30k ohms and 5 volt speaker, but not sure if that's accurate.

Besides that, what would be a way to connect this thing to the output of a modern audio interface with a 1/4 TRS jack, or would I need to rig something up to get this speaker power, etc?

Images are attached.

Gyro:
If it has a moving coil transducer, then it is open circuit (hopefully connection rather than coil). On the other hand, if it's really thin then it might be some sort of piezoelectric transducer (hopefully not an electrostatic speaker of some sort).

Try measuring its capacitance instead.

If it is piezoelectric, you might get away with just a parallel resistor to prevent it from looking like a purely capacitive load.

Humanoid:

--- Quote from: Gyro on April 23, 2021, 09:01:40 pm ---If it has a moving coil transducer, then it is open circuit (hopefully connection rather than coil). On the other hand, if it's really thin then it might be some sort of piezoelectric transducer (hopefully not an electrostatic speaker of some sort).

Try measuring its capacitance instead.

If it is piezoelectric, you might get away with just a parallel resistor to prevent it from looking like a purely capacitive load.

--- End quote ---

Thanks.

I checked capacitance. It took a few seconds and registered about 10nF. I could hear clicking sound out of the speaker when the probes touched it, so it seems to work.

I found an excerpt from an article about it. It says it has a "crystal element". Apparently these were used in hospitals to put under patient's pillows so they could listen to the radio and not disturb others. My guess is it may have been plugged into a headphone jack, though not sure if old radios used one TS plug for both headphones and a speaker.

Image attached of an ad I found in an old magazine. Seems to only use .01 watt of power.

Ian.M:
30K @1KHz, 0.01W, and P=V2/R gives V of 17.3V RMS or 49V pk-pk It seems likely that it wont be sufficiently excited by a modern headphone jack.   OTOH you probably don't want to push a vintage speaker that hard, so 8.7V RMS, 24.5V Pk-Pk is probably plenty.   Its still going to be a PITA to do that without a matching transformer.  Some testing with a signal generator capable of at least 10V pk-pk is called for before you commit to anything.


IMHO the original installation instructions probably called for a dummy load resistor on the output transformer and a coupling capacitor chosen to drop the signal voltage to what the BA-301 could handle, from the output valve anode, or possibly one from each anode if the set had a push-pull output stage.

Gyro:
The 0.01W is presumably a maximum rating. If you could hear clicking during a DMM capacitance test then it's probably reasonably sensitive.

You need very little volume for a pillow speaker (that's kind of the point). I'd just try it and see if it is loud enough. From the screenshot, it just came with an ordinary phone (headphone) plug. Headphone outputs of the time didn't output much voltage if they were mainly designed for magnetic headphones.


EDIT. If you are wanting to experiment with connecting it to a normal stereo headphone output, you could try a series 33R resistor from each channel to one lead and return the other lead to the barrel connection. That will give enough resistance to provide a stereo to mono conversion and help isolate the capacitive load. If it works, fine. If not, then you'll have to decide whether it's worth going to more expensive solutions for greater volume.

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