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Old 5th Sep 2017, 1:31 pm   #1
greenstar
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Default Unusual headphone

I have this S G Brown single earpiece from a box of junk at a rally. I am interested to know what the mechanism is, and what is missing. I have the cap.
The back is stamped, S G Brown, Acton, London. No BBC stamp. The windings read about 3.5K.
Tony.
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Old 5th Sep 2017, 1:38 pm   #2
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Default Re: Unusual headphone

Type A, adjustable reed?:

http://www.richardsradios.co.uk/sgbrown.html

Lawrence.
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Old 5th Sep 2017, 1:40 pm   #3
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Default Re: Unusual headphone

Can you post a head on view looking straight into the front please.
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Old 5th Sep 2017, 1:43 pm   #4
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Default Re: Unusual headphone

More views
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Old 5th Sep 2017, 1:45 pm   #5
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Default Re: Unusual headphone

Thanks.

Looks like Lawrence is right.

I guess you're missing the diaphragm?
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Old 5th Sep 2017, 1:52 pm   #6
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Default Re: Unusual headphone

I found this:
1910/11 He formed a new company, S. G. Brown Ltd, to manufacture telephone equipment. With his wife's assistance, he designed a telephone relay, an improved receiver, and an effective loudspeaker (the Browns being first to use this name for the device). He had a small workshop in Houndsditch for the manufacture of the type-A reed headphone which became famous throughout the world.
https://www.gracesguide.co.uk/S._G._Brown

Can they be this early? Sorry Graham, to add, looks like the diaphragm is missing. I doubt it's easy to repair.

And
'Many thousands of the type-A headphones were being manufactured for use during WW1'.
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Old 5th Sep 2017, 1:54 pm   #7
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Default Re: Unusual headphone

EDIT: Post crossed.

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Old 5th Sep 2017, 2:24 pm   #8
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Default Re: Unusual headphone

Surviving S G Brown headphones are plentiful. I have at lease four pairs. None of them are of the reed type though, so these may be less common.

Making a diaphragm might not be too difficult if we knew what it looked like. Could it be just a plain disc?
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Old 5th Sep 2017, 2:56 pm   #9
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Default Re: Unusual headphone

Richard's radios says:
'Headphones Type A. I have also been given a set of low resistance 60 Ohms (120 total) headphones which have a sensitivity adjustment on the back of each earpieces.They are each stamped with patent no.29833-10 which refers to the 1910 patent. These have aluminium cone shaped diaphragms with a central screw and although not marked as such I believe that these are Type A headphones'.

The number on the back of mine is 20533, which suggests an earlier patent, although of course they may have been made later. The cone shaped diaphragm sounds difficult to duplicate. Also mine is high resistance, although they were probably made with various impedances. He moved to North Acton in 1915, according to Grace's guide, so mine will be post that.
I don't mind it as it is. This is worth keeping for its' interest. Be interesting to see one that is intact.
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Old 6th Sep 2017, 10:51 am   #10
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Default Re: Unusual headphone

It may be of interest, I've just found adverts for the Type A in Amateur Wireless, October 1922 (American Wireless History Website). It seems the type A was available in 1922 new and government surplus, with the type D. The A was available at 120 and 8000 Ohms.

I am wondering why the reed type were made alongside the more familiar design, why they were made in such quantity and for so long, and why they were superseded.

Thanks for your help folks. Although this was a small find it is a fascinating one.
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Old 6th Sep 2017, 11:04 am   #11
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Default Re: Unusual headphone

And, before I let go of this, from the Richard'sRadios website, from Patent 29833
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Old 14th Sep 2017, 3:36 am   #12
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Default Re: Unusual headphone

My S G BROWN Type "A"
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Old 14th Sep 2017, 6:03 am   #13
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Default Re: Unusual headphone

Quote:
Originally Posted by greenstar View Post
I am wondering why the reed type were made alongside the more familiar design, why they were made in such quantity and for so long, and why they were superseded.
The reeds are resonators. These are narrowband audio transducers and act as audio filters. At the same time the resonator gives them unusually high efficiency. This makes them very good for receiving Morse transmissions. The operator could set his receiver up, and then adjust the tuning knobs on his headphones to peak the audio filter on the tone he was receiving.

In the days when sets hadn't got much selectivity this made a big difference and the high efficiency could make up for low gain.

A trick I was shown in a crowded band was to tune the transducers of a headset differently, so you got one signal in one ear and a different one in the other!

These transducers were a big advantage until narrow, multi-crystal filters became common and could do the selectivity in the receivers without external assistance. This gave them a long manufacturing run until other filters supplanted them. They weren't good for speech and even worse for music, so they weren't general purpose.

Morse aficionados still treasure these phones for simple QRP transceivers. It's surprising how much DSP horsepower and gain is needed to replace them in current gear

David
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