BUILD THIS Beer-Keg Radio FOR YOUR GAME ROOM (Jun, 1938)
BUILD THIS Beer-Keg Radio FOR YOUR GAME ROOM
By ARTHUR C. MILLER
NOVEL as well as serviceable, the beer-keg radio described on these pages will make a useful addition to the furnishings in your game room. It can be used either as an end table or as a refreshment stand, and, since it is an entirely self-contained unit, operated by dry batteries, it can be carried onto a porch or even into the yard when warm summer days and evenings make this desirable. If you build this five-tube set carefully, it will give excellent reception from stations 1,000 miles or more away.
The unusual cabinet that houses the chassis, speaker, and batteries of the powerful superheterodyne circuit, is nothing more than an inexpensive ten to fifteen-gallon wine barrel, which can be purchased from any mail-order house. Making the barrel resemble a beer keg requires simple, inexpensive treatment which will be described later.
To transform the barrel into a receiver cabinet, first saw it into two sections at a point approximately four inches down from the top. The smaller section is the lid, to the underside of which the chassis is fastened. In front of the lower section of the barrel, cut out a hole five and a half inches in diameter. This will serve as the speaker opening. The batteries rest on the bottom of the same section, concealed from view.
The dimensions of the chassis will depend to some extent on the size of the barrel used to house it. The reader will find it an easy matter to bend a chassis out of sheet aluminum, or, if he prefers, he may purchase a standard five-tube chassis from a radio-supply house.
To assure maximum sensitivity, the author made use of the latest tubes available for battery operation. For maximum power, iron-cored intermediate-frequency transformers having an amplification factor nearly twice as great as the standard air types were used. The antenna, oscillator, and intermediate-frequency coils are shielded to insure good stability and ventilated aluminum cans shield the first three tubes from any stray couplings that might exist in the circuit. High-frequency currents are prevented from entering the audio-frequency stages and causing distortion by inserting a 20-mh. choke into the plate lead of the 134 tube and by-passing it with a .0002-mfd. mica fixed condenser. Mica by-pass condensers also have been included in the plate circuit of each of the two audiofrequency stages.
A compact 100,000-ohm variable resistor regulates the amount of the bias on the grids of the 1A6, 1A4, and 1B4 tubes. For tuning, a standard .00036-mfd. two-ganged tuning condenser is used in conjunction with an adjustable padding condenser. Mount the padding condenser on a white ceramic base to avoid high-frequency losses caused by leakage from inadequate insulation.
The two double-tuned intermediate-frequency transformers have been adjusted at the factory for a frequency of 456 kilocycles. Variations in the wiring of the set may cause the setting to be altered slightly. If this occurs, you can easily readjust the mica trimmers by means of the two nickel-plated screws recessed into the top of each transformer.
Batteries for the beer-keg radio are of the medium-duty type. A three-volt, dry-pack “A” battery of the plug-in variety heats the filaments of the tubes. To reduce the supply of current to two volts, a wire-wound, two-ohm filament resistor must be used in the “A” line.
Since an electrodynamic type of speaker would require a separate six-volt storage battery, the author selected a six-inch dynamic speaker of the permanent-magnet variety which does not require such a battery. The speaker should be mounted first on a piece of wood about seven and a half inches square and three eighths of an inch thick, with a six inch hole in the center. The panel-mounted speaker then can be screwed to the inside of the barrel, just behind the hole cut for it. If the reader wishes to improve the appearance of the unfinished kegâ€”kegs are usually of white oak with heavy blued-steel hoopsâ€”he can stain it with a light walnut finish, and then polish it with a coating of wax. The metal hoops can be either chromium plated or, if that is not practical, they can be finished in black enamel. Drill holes through the top of the keg to admit the shafts of the control knobs.