By Jim Liles, K9AXN

We have received numerous inquiries regarding SR-2000 S-Meter insensitivity. First, the procedure for adjusting the S-Meter included in the operator's manual is a bit lacking. The correct procedure is to turn the AGC threshold pot, R-46 fully clockwise, zero the meter with the meter zero pot, and then turn the AGC threshold pot CCW until the meter just moves. This is a three step process and you are finished.

Before doing anything, check the resistors R-118, 119, and 121. They are critical, especially R-118. You can find R119 the 82K resistor directly below L15, R121 3.3K under the plate that holds the Meter zero pot, and R118 5.6K at V8B. Disconnect one S-Meter lead and measure all three after unscrewing the pot plate and isolating it from ground, you won't have to unsolder anything.

Bear in mind that the AGC/S-Meter tube is a 7059 which is a 13.5V tube running at 12.6V if all is well and 90V on the plate. After you perform the adjustment above, remove the S-Meter tube V8A and see what the S-meter indicates. It should be above +60Db, pegged. Whatever it reads with the tube removed is the highest reading possible. You will probably wonder why the meter is pegged when you first turn it on. When first fired up, the B+ will be approximately 320V until the tubes warm up and draw plate current. Then it will drop back to 280V (The meter is driven with a bridge). Tube V8 is the one tube in the SR-2000 that must be hand selected for S-Meter performance. If the meter does not peg with V8 removed replace it and do the above adjustment then pull the tube and repeat until its right.

The S-Meter will be quite accurate when you are finished.

Kindest regards Jim K9AXN


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