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A "Knock-Out" 3-Tube Set
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used with adaptors for the UV-190/s, for which tubes this particular set was designed. A single ten-ohm rheostat controls all tubes through filament lighting jacks of the most easily obtainable type. C2, the anti-squeal condenser, is a .0005 Micadon. The detector is a De Forest stand with a Fada cat-whisker and arm. Forty-five volts were used on the plates of the tubes, and four and a half volts on the filaments.
BUILDING THE SET
OUR first experiments with this apparatus were conducted with the set built up on a base-board, as shown in Fig. 3. Such temporary construction is always a good idea, and is invariably followed by veteran experimenters. It facilitates various tests, and makes possible the definite designing of the ultimate apparatus. The base-board measured sixteen by ten inches, and Fig. 3 shows very plainly the distribution of the instruments. It will be noted that, even in the temporary installation, wiring has been done with at least a semblance of care. Neat wiring consumes a bit more time, but it is worth the extra trouble. In the case of inoperation, it eliminates careless running of leads as a possible and frequent source of difficulty.
Figs. 4 and 5 show the completed set of so simple design that any one can follow our instructions. It was with simplicity in mind that Radio Broadcast has eliminated all constructional gymnastics, such as shelves, brack
fig. 2
The "Specific Circuit." This is the modification of the fundamental circuit used by Radio Broadcast in building the set described
ets, etc., which often strain the ability of the average fan. Straight base and panel mounting has been adhered to throughout, with the possible exception of Ti, which may be mounted on a three inch square shelf resting on top of the reflex audio transformer, if the experimenter is unable to accomplish the feat of securing it to the variable condenser.
Fig. 6 is a working drawing of the panel. The comparatively large hole, if inches in diameter, passing the Ballantine Varioformer (which should be of the panel mounting type) is made by drilling a circle of small holes.
The base (see the insert of Fig. 6) is 13 inches long, six inches wide, and f inch thick. This thickness makes a firm support for the panel which is fastened to it by three screws, f inch up from the bottom. This, in conjunction with rigid wiring, holds the panel quite firmly. The base, one inch shorter than the panel, makes possible the use of a cabinet with grooved sides into which the panel is slid.
Fahnstock clips have been employed for the battery connections, and are screwed to the rear of the base, between the audio transformers as shown in the insert. "A" indicates the A battery terminals and " B" the high voltage connections.
construction hints
THE panel should, of course, be drilled, grained if desired, and fastened to the base-board as the first step in construction. All panel instruments, Ci, Ti, T2, detector,