Porto-Products, Inc. SR-600
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STAGE GAIN MEASUREMENT PROCEDURE
Lettered terminals in illustrations correspond to similarly lettered terminals on the circuit diagram.
I.F. 455 KC.
The amount of amplification or " gain " of each of the stages of this receiver may be measured with an A.C. Vacuum Tube Voltmeter or a " channel " type instrument containing a tuned and calibrated amplifier.
PROCEDURE: It is exceedingly important to adhere to the procedure outlined below since the accuracy of these measurements will be affected to a considerable extent by the failure to establish proper operating conditions. 1. Be sure that R.F. and I.F. stages are carefully and accurately aligned by utilizing the alignment procedure given above. 2. Connect Signal Generator as shown below. 3. The values of stage gain which are given here were measured with a fixed bias of 3 volts on the control grids of ali R.F. and I.F. tubes which are connected to the A.V.C. circuit. Therefore, these values are not intended to indicate the full capability of a stage but they will serve as a convenient basis for determining proper operation. In order to duplicate the fixed bias voltage, connect the negative terminal of a 3 volt battery to A.V.C.at
Black lead to the loop antenna and connect the positive battery lead to receiver chassis. Set Signal Generator for operation at 600 Kc with 400 cycle modulation and carefully tune radio receiver to this signal by using an output meter to indicate peak output. If a local station interferes. set generator to a nearby frequency and re-tune the receiver. R.F. and I.F. circuits are slightly detuned when contact is made with an instrument probe and this action, which is indicated by a change in the output meter reading, may seriously affect the gain measurement. Therefore, it is important to adjust the associated circuit trimmer for a maximum output meter reading and to set the input signal level to a convenient reference point on the gain measuring instrument while the probe is making contact. After removing the probe it is again necessary to adjust the trimmer so as to obtain the same output meter reading and thereby assure that the signal voltage at the specified point has not changed as a result of circuit de-tuning. When using a " channel " type instrument, carefully tune it for maximum output at desired frequency before making measurements.
ALIGNMENT PROCEDURE 1. " With the gang condenser fully meshed, dial pointer should be in the position indicated by the last division below 55 on the dial.
If it is set incorrectly, release pointer clip on dial cord and reposition pointer. 2. Connect on output meter across the speaker voice coil or from the plate of the 50L6GT tube to chassis through a. l Mid. condenser. 3, Connect ground lead of signal generator to receiver chassis. CAUTION: If your signal generator is designed with an AC - DC power supply, connect ground lead of signal generator to receiver chassis through a. 25 mld. condenser, 4. Set volume control at maximum volume position and use a weak signal from the signal generator,
Measured with voltmeter having sensitivity of 1000 ohms per volt except where indicated by (*). The (*) symbol designates a vacuum tube voltmeter measurement.
DIAL TUNED TO 540 KC. VOLUME ON FULL WITH. NO SIGNAL
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