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How to Build a Two-Stage Radio-Frequency Amplifier
6 1
FIG. 13
To obtain complete neutralization, the coils should be turned at an angle to the bus bar as shown here. The value is approximate. Actual test will determine the correct placement
— and we've surely tested more than a few.
This radio frequency amplifier is especially adaptable for use with a loop.
In a future article the construction of a detector amplifier unit will be described which, while it may be used with any tuner, is especially intended for use with the radiofrequency amplifier described here.
General Additional Notes
THE use of a loop with this amplifier wil1 naturally reduce the strength of received signals and therefore not a great deal of distance work will be accomplished when the loop is used.
However, for sharpness of tuning, and quality of reception, the results when a frame antenna is used are difficult to equal where local stations are being received. Loop reception on locals is desirable where tone quality and clarity are prime factors. The placement of the loop near the antenna-ground wires (which may be connected together)
loosely couple it to the antenna circuit which increases the volume but may effect the quality of reception because this connection will cause some static to be received when any is receivable.
The tuning of the first condenser when a loop is used will depend largely upon the number of turns of wire wound on the loop.
For all practical purposes, a standard pancake loop 30 inches square, wound with 16 turns of wire spaced f of an inch apart will suffice covering the entire broadcast wavelength band.
If variable plate neutralizing condensers are used, some other means for mounting them on the brass bus bar strip must be arranged. It is not advisable to mount them on the panel unless such an arrangement permits of the use of very short leads. The adjustment of this neutralizer is very rarely changed, so that for all practical purposes, the back-of-panel mounting will prove quite satisfactory.
Double Circuit Jack Rear of Jack
LOOP JACK DETAILS FIG. 14
When a jack is incorporated for the use of a loop, the circuit must be altered so that the antenna coupler may be automatically thrown in the circuit when the loop is not being used
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