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How to Make a One-tube Reflex Set "That's a Knock-Out"
attachment" — if results are satisfactory the more or less cumbersome aerial may be dispensed with.
INSTALLATION
(A) Connect both A and B batteries to their respective binding posts — care being taken to have the polarity correct. Use number 18 or heavier rubber-covered stranded wire and keep all leads short and direct.
(B) Insert the vacuum tube and Amperite in their sockets and ascertain that positive contact is assured; it would be well to bend up the socket springs slightly in order that they may exert considerable force upon the vacuum tube pins.
(C) Connect a suitable ground to the negative A binding post and an aerial such as described above to the aerial binding post.
OPERATION
(A) Place the output plug in the jack; the vacuum tube should light instantly.
(B) Set both dials to the same point and adjust the crystal detector until a fairly strong "click" is heard.
(C) Slowly vary both dials between maximum and minimum position, maintaining them in approximately equal relation to each other.
(D) When a station is heard, turn the grid variable condenser and center it for stronger response, following this by adjusting the detector for better results.
(E) Further manipulation of the crystal for the most "sensitive" adjustment will improve both the quantity and quality of reception.
(F) With an average antenna, both dials will nearly coincide for any wavelength. No difficulty will be experienced in tuning both circuits to the same resonant frequency, as clicks (from crystal adjustment) are heard only when the grid and detector circuits are in tune with each other; being loudest when the circuits are exactly in resonance.
(G) When the crystal contact is "off, "the receiver may oscillate, especially if headphones are used while tuning. There are a few methods of stopping this but as it is rarely annoying special precautions are not necessary.
FIG. 12
The sub-base from the rear
(H) On strong signals, the condenser in the crystal detector circuit is not very critical, but it has a well defined maximum resonant peak which may be passed over if this control is varied too rapidly.
(1) It is the combination of controls that makes for selectivity, and both are quite critical on weak stations.
(J) The crystal adjustment is important not only for strength and clarity of signals but also for selectivity.
(K) On a stiff piece of manila paper provide three columns to record :
(i) Stations call letters, (2) Ti dial settings and (3) T2 dial settings. This record may be permanently placed on the inside of the cover (under transparant celluloid, for example) and referred to when the program of a certain station is to be tuned in.
CARE AND UPKEEP
THE filament and plate batteries should be kept at the proper voltage and B batteries which show a drop of more than 25 per cent, should be discarded.
Inspect all connections occasionally and clean wiping contacts; such as in the vacuum tube socket, in order that there will be no loss due to contact resistance.