Radio age (Jan 1927-Jan 1928)

14 RADIO AGE for November, 1927 The Quadrode — A New Super-Heterodyne By Frank Freimann Figure 1. — Back panel view of Quadrode Superheterodyne WE are bringing to our readers a new super-heterodyne which we know will be met with enthusiasm. We have long been wondering why the Quadrode Vacuum Tube (four electrode) was not adapted to the many possibilities which this interesting tube affords. A month ago we started working towards a super-heterodyne of a highly efficient nature which would be simple enough to attract the man who, because of its complicated character, has been afraid to build a super-heterodyne. We planned a superheterodyne simple enough in construction to be built by one who has had little or even no experience with radio receivers and yet a super-heterodyne as generally efficient as the most complicated of receivers we know today. And here the Quadrode Vacuum tube immediately presented itself as the solution for a simple mixer circuit. Fortunately we already have on the market a highly efficient intermediate frequency amplifier which we immediately decided to use in our new receiver, due to its simplicity and high amplifying ability. The amplifier was described in the October issue of RADIO AGE and is already familiar to the radio experimenter as the S-M 440 Jewelers Time Signal receiver, manufactured by SilverMarshall, Inc. This instrument itself reduces the complications of the superheterodyne many fold. Instead of having a series of transformers to wire up into an intermediate amplifier — complications which entail dozens of connections, not to mention the worries as to whether or not the transformers are matched — the S-M 440 amplifier merely has eight connections to be made to the associated parts of the receiver. The one tube mixer, the S-M catacomb, and a simple two-stage audio amplifier constitute the unique Quadrode Superheterodyne shown in the photograph, Figure 1. The special tube which serves the dual purpose of detector and oscillator more efficiently than the conventional two-tube circuit, needs perhaps some description as very little publicity has been given this very excellent tube in this country. In foreign countries its merits are more fully recognized and the tube is more commonly in use, whereas here in America there has been no such device developed and made available until this late date. The Voltron Quadrode we are here employing is the development of the K & H Electrical Corporation, and consists of a very substantial filament, two grids, one on each side of the filament, and a common plate. The characteristics of each side of the tube is practically identical, that is, the inter-electrode impedance and capacity is the same. Double grid tubes that have previously made their debut on the market are the type having one grid within the other. A tube of this kind has two decidedly different characteristics, one equivalent to a High Mu (high amplification and very high plate resist ance) and the other a Low Mu; therefore the tube does not lend itself to all purposes. The Voltron Quadrode looks externally exactly like any other tube of the more common type except for the base, which has five points instead of four, so spaced that the tube can be plugged into a socket designed for a five prong type of tube. The connections on the socket can be followed according to the way the socket is marked except the cathode connection (the extra connection) which is the additional grid. The plate resistance of the tube is about 20,000 ohms. The Quadrode Super-heterodyne is not only simple in construction but easy in tuning as well, since there are no regeneration controls and since there is no possibility for the detector circuit to oscillate; yet regeneration is always present in the detector circuit, thus increasing the sensitivity and selectivity of the set. The two dials run together over the whole wave length range with a deviation of less than five points. This makes the set particularly easy to tune because one knows that the dials are in resonance as long as the numbers on the dials correspond. The set can be used on either an inside loop aerial or a short outside aerial. Most of the experiments were conducted with a wire connected through a small condenser to the house lighting system as an antenna. In this manner KFI was received with enough volume for good loud