What was a mirophone "hummer"? - Printable Version
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What was a mirophone "hummer"? - Antipodal - 10-04-2020
Hullo Everyone,
I've been reading a "Radio News" from November 1938 and am interested in the article there entitled "A Vest Pocket Receiver" on page 8. The article is written by an English radio writer (G. Bradfield) but there is frequent use in the article of parentheses by the Editor of "Radio News"to translate the English wireless terms into American radio terms.
The circuit of this receiver is ,therefore, an English one using two sub miniature tubes and is unusual in that it uses only one battery of 4.5 volts. This provides filament voltage and bias to the two tubes.What provides the H.T.?
The 4.5 volts also passes through the primary of a vibrator transformer to be interrupted by a "microphone hummer" to earth , this interruption serving to produce an alternating current in the secondary of the transformer to produce about 30 volts of A.C. , rectified in this circuit by a dry disc rectifier to provide H.T. to the anodes of the tubes.Much is made in the article of the "soft" interruption provided by the "hummer".
In the article the English writer mentions a "microphone button mounted on a small moving iron unit (such as were once used for cheap loudspeakers) " as the circuit interrupter.
At this point in the article the , I presume American ,editor adds ,in brackets, "(A microphone hummer can be used,also.)"
Here in New Zealand I have not found anyone who can tell me what the English " microphone button " is ,so I am hoping someone ,perhaps from U.S.A. can tell me what the American editor means when talking of a "microphone hummer".
Something tells me that it might be associated with a carbon microphone to activate the granules.If anyone knows I'd be pleased to hear from you. Cheers and all the best,
David
RE: What was a mirophone "hummer"? - morzh - 10-04-2020
https://www.radiomuseum.org/r/gener_raco_microphone_hummer_oscillator_572_b.html
It explains it well.
Basically an oscillator using a carbon microphone in the feedback.
RE: What was a mirophone "hummer"? - Antipodal - 10-04-2020
Hi there Morzh,
Thanks so much for this.Very well explained there ,and comforting to know I was on the right track.That said I have never come across one here at sales or swap meets.
But if you don't know what you're looking for you often don't find it.So I'm on the lookout now.
Thank you again and cheers,
David
RE: What was a mirophone "hummer"? - Chas - 10-04-2020
I've "cross-posted" a very recent post in ARF on what is a very similar device to help us rediscover old technology.
I have identified the "microphone" as a form of "Skindervicken Button" a popular product of the '20's (US) see World Radio History and search that name...
The post is What is This?
Because of the external hardware on the device in the ARF post it may well be a "hummer"...
https://antiqueradios.com/forums/viewtopic.php?f=2&t=385065
Thanks! Chas
RE: What was a mirophone "hummer"? - Antipodal - 10-05-2020
Thank you Chas and what great recall to find that obscure reference too.I know what I'm looking for now.Thank you again