10-04-2020, 12:36 AM
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
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
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