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12
RADIO AGE for November, 1927
Back-panel view of the completely assembled Camfield Super-Selective Ten
The Campfield Super-Selective Ten
RADIO is, and as it is most progressing, and we have before us today the Camfield Super-Selective Ten, which combines a Tuned Radio Ferquency circuit and the Super-Heterodyne.
This remarkable receiver functions best when used with an aerial and ground. It is well known that even the most diminutive of aerials picks up more current than a loop. The only reason aerials and supers were not used together long ago was that the super refused to differentiate between stations. It could not handle all the power collected by the antenna.
By consulting the diagram one will readily see how this trick is possible. Three stages of radio frequency amplification are placed ahead of the detector, one untuned, the others governed by a three gang condenser.
The untuned stage acts as a ballast, stabilizing the circuit and greatly retarding unwanted oscillation. This receiver positively will not squeal nor howl when being tuned.
Tuning is extremely sharp, due to the employment of a new device on the market, a 10 Kilocycle Band Pass Filter. This device prevents stray waves from visiting the second detector. Only the frequency to which the first detector is tuned is allowed to pass. This is quite desirable for use in metropolitan districts for it enables one to tune right through the high powered ether paralyzer next door and drag in the favorite back in the old home town. The Camfield Super-Selective Ten is the first receiver to make use of a filter circuit of this sort, and by the way it works it will not be long till there are plenty of others.
Tone quality is perfect. Sharply peaked intermediates are avoided and the filter allows a sufficient breadth of channel to let the overtones and musical side bands pass undisturbed. This means that the full musical scale is faithfully reproduced, from the deepest growl to the highest squeak.
Now that we have made an appeal both to the man who hates QRM and the lover
of fine music we will also include the midnight prowler who is satisfied with nothing short of Manila or Cape Town. This receiver is sensitive, very much so. There are three stages of radio frequency amplication ahead of the first detector. No matter how many tubes after this first detector, signals are heard no farther than it is able to detect. There is a minimum point of audibility, below which no sound is heard. With the additional radio frequency tubes ahead, this point of audibility may be considerably lowered giving phenomenal range. D. X. is a matter of selection of tubes, batteries, aerial and ground, coupled with patience and skill on the part of the operator. Many new transAtlantic records will be made this winter with the Camfield Super-Selective Ten.
There are only two tuning controls, because most of us have but two hands. That is all that is needed anyway for they do the work to perfection.
The three T. R. F. condensers must be
9V . O90V*
Schematic diagram of the Camfield Super-Selective Ten