for R-4, R-4A, R-4C, SPR-4, RR-1, RR-2
Click to enlarge pic
Picture source: R.L. DRAKE Company
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Installation of a LA-4 will result in a output of 1 mW nominal into a 600 ohm balanced line. |
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Output level adjustable by internal pre-set level control |
| Interfaces low level audio to RTTY terminal unit or phone line that requires 600 ohm balanced/unbalanced inpu |
IMPORTANT NOTE :
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R1 is 150 K in R-4, R-4A, R-4B |
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R1 is 100 K in the R-4C, SPR-4 and RR-1 |
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R1 is 47 K in the RR-2 |
LA-4 Amplifier ( Communications Channel)
Alignment Procedure
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Tune in a signal having a level of about 50 micro volt on 40 meter band. Adjust frequency knob for a frequency of about 1kHz
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Connect 600 ohm resistor across ungrounded output connections. Connect an oscilloscope and AC VTVM across 600 ohm resistor. Make sure that there is no ground path between scope voltmeter combination and receiver chassis or one side of transformer will be shorted out.
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Adjust R8 for 1mw across 600 ohm resistor (.77 volt RMS), and make sure waveform is clean.
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If output is too high, R6 can be changed to as high as 500 ohm to center pot.
