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RADIO AGE for January, 1927
The Magazine of the Hour 25
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Clough 7 Tube Super Result of Much Research
Several Novel Features Make It Highly Desirable
CONSIDERABLE research work has been done in the past few years on the superheterodyne, principally by independent engineers who have seen in this type of receiver the culmination of all ideas concerning distant reception, freedom from interference and, lately, excellent audio quality in the loud speaker.
With this in mind we take pleasure in announcing a recent design by Kendall Clough, of the Research Laboratories of Chicago, of a seven tube superheterodyne in an exceedingly compact form which has given, under Radio Age laboratory tests, perhaps the highest account of itself of any of the types of similar receivers of the same number of tubes. In addition the quality of the audio end of the receiver is excellent, and surpasses anything we have yet tested.
These remarks may seem rather radical for a magazine of conservative tendency, but the facts speak for themselves. We are always on the lookout for
By F.A.HILL
{Associate Editor)
something better than the ordinary for our readers and in this case we believe we have found it.
Inspection of the schematic circuit of this set will not disclose any trick stunts. Instead the reader will observe that it is the conventional superheterodyne with a shielded first detector, a shielded oscillator, and antenna coupling instead of a loop. These features (the first two), make for decreased local pickup of stray energy, while the latter permits the use of the receiver in a congested locality where a loop's directional propensities would be set at naught due to the construction of the building in which the receiver was located. It also permits using a very small energy collector, an antenna of from 4 to 25 feet in length.
However the feature to which most importance should be attached is the method of feeding the oscillator a positive grid bias to a point where the plate circuit of the oscillator will take the same space current with the
tube oscillating as it does with the tube not oscillating. When this point is reached (as will be explained further in this article) the even harmonics of the oscillator will have been eliminated, leaving only the odd ones which will be greatly robbed of their energy.
Peaking the Filters
ANOTHER point to be consid. ered in this particular superheterodyne is the fact that a great deal of work was expended on the intermediate stages by Mr. Clough who had felt there was much to be desired in peaking long wave filter circuits and who set about designing a new method of doing this work. Beside the accuracy of peaking in the intermediate stages, the question of field intensity of the transformers themselves was fully investigated with a view to finding the effects of coupling between the intermediate transformers; the presence of shielding; the effect of non-uniform tube capacities and a host of other problems with which the