Hallicrafters SX-117, Руководство по ремонту, Страница: 9 / 51

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2-3-2, AUDIO POWER METER
An audio output meter such as the General Radio 1840A (my choice) is all that is needed.
There are many that are up to the task. The key features are: Internal variable load (at least 3
ohms to 1.5k), variable full-scale power, 2mw to 20w and a meter calibrated in watts and DB.
Fully self-contained no power no batteries. The majority of the receiver test specs involve a fixed
signal input and a minimum or fixed audio output across a fixed load. Other specs involve a
change in audio output across a given load due to a change in input signal. All of these
measurement requirements are satisfied by a good audio power meter.
For my bench setup I have a standard ¼ inch phone plug which goes to a switch. The switch
selects either a speaker or the audio power meter. Like the SX-117 most of the equipment I work
on (Hallicrafters SR series) has a front panel phone jack that disconnects internal speakers. I
have an adaptor phone jack with clip leads for working on various other radios. A side benefit
of using an audio power meter with built in load is, you do not have to listen to the constant
drone of the receiver. Switching in the speaker allows you to quickly find the signal when you
change frequencies.