Signals & Noise (Letters to Editor) (Jun. 1992)

Reading, Writing, and Radios

Dear Editor:

I very much enjoyed "Tuning in to Yesterday" in your January 1992 issue. I want you to be aware of my publication, Antique Radio Classified, a monthly magazine with over 7,000 subscribers that is devoted to the antique radio collecting community. A typical issue contains about 90 pages, and includes 600 classified ads, ads for services and hard-to-find repair parts, auction prices, flea market and collector club information, plus 20 pages of articles. As well as covering early radio, Antique Radio Classified covers art deco '40s and '50s radios, collectible transistor radios, early television and telegraph, early amateur equipment, and books on all these subjects.

Being the largest publication world wide devoted to the antique radio com munity, we respond to over 500 inquiries each month with a free sample copy of our publication. Address requests to:

Antique Radio Classified, P.O. Box 2-V42; Carlisle, Mass. 01741

John V. Terrey, Publisher & Editor

Finer "Tuning"

Dear Editor:

We enjoyed the nice photos and captions of Jon R. Sank's "Tuning in to Yesterday--Vintage Sets from the Golden Age of Broadcasting" in the January issue. We would like to point out, however, that the caption for Harry Houck's amateur set contains errors:

A spark was created when the key was depressed, causing an undamped--not continuous wave (cw) wave-train. In those days, cw and Morse code were not synonymous words, as they are today. Also, the sound of such signals in the head phones was not clicks, but raucous buzzing sounds corresponding to dots and dashes of Morse code. It is interesting to note that Harry Houck was Major Armstrong's assistant in the invention of the superheterodyne receiving circuit.

The RCA Radiola 60 did not use a doublet antenna such as the Atwater Kent Model D shown with it. Doublet antennas were brought out in about 1933 to provide noise-free short-wave reception on "all wave" home radios which were becoming popular that year.

-Thomas M. Turner; Watervliet, Mich.

Addendum

Following are some notes on impedance considerations for the First Sound Reference II Passive Preamp (reviewed in January) inspired by comments I received from a reader.

The attenuator impedance and con sequent input impedance of the First Sound preamp is 20 kilohms. This is on the low side of what most tube circuitry will happily drive. The most noticeable effect will be a possible premature low-frequency roll-off due to the size of the output coupling capacitors used in typical tube circuitry. Correspond with the manufacturer to get advice on their product driving 20 kilohms. Most, if not all, solid-state circuitry will drive 20 kilohms with no problem.

Driving low-impedance loads, such as power amplifiers with input impedances in the range of 10 kilohms, isn't really a problem except when the attenuator is turned up to full rotation.

Then the amplifier's input impedance is in parallel with the attenuator impedance, making the overall input impedance to the source come down to about 6.7 kilohms. This would not be recommended for tube sources but, again, would be okay for solid-state sources. Another consequence of a low-impedance power amplifier load on the attenuator is that the attenuation steps near fully clockwise will be coarser, whereas the attenuation steps down in the lower range of the control's rotation will be less affected.

-Bascom H. King

(adapted from Audio magazine, June 1992)

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