Airspeed FM-25 Руководство пользователя - Страница 15

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1. Remove the back cover via the four (4) #2 Phillips screws in order to access the Bias control on

the top-right side of the chassis.

2. Set your DMM (digital multimeter) to DC mV, or simply DC V if it is an auto-ranging meter.

3. Plug the black DMM probe into the Black Bias Test Point. Plug the red DMM probe into the Left

Pair – Red Bias Test Point.

4. Turn the amp's global MASTER volume all the way down (off).

5. Ensure a proper load is connected to the Speaker Output and the impedance selector matches

the load.

6. Turn on the amp via the Power On.

7. After a 60 second warm-up, flip the Standby (STBY) switch to ON.

8. Check the mV reading on the DMM.

9. For a 6L6GC loaded amp it should be between approximately 30 mAV, which is equivalent to 30

mA per tube. Amps are setup at the factory at 30 mA per tube, however it is safe to run up to 40

mA per tube.

10. While watching the DMM, adjust the bias setting with the Bias control on the top right side of the

chassis. Counterclockwise rotation lowers the bias, whereas clockwise rotation increases it.

11. Take note of the Left Pair reading, then plug the red DMM probe into the Right Pair – Red Bias

Test Point. Compare the Right Pair reading with the Left Pair – they should be within ~5 mA of

each other.

NOTE: If you see strange numbers, here are some possible reasons:

1. If one side reads 0 mA and the other looks good – then likely both tubes on one side are out.

2. If one side reads about half of the other side, then just one tube is out.

If the two readings are close, just not within ~5 mA, then the tubes are not properly matched and

should be replaced. One can also swap one tube from each side in order to try and balance the

readings more.

FM-25 Specifications

The Airspeed FM-50 Amplifier (Head unit)

25-Watt Class A/B Head

•

Two (2) 6L6GC power tubes, six (6) 12AX7 pre-amp tubes, one (1) 5U3B rectifier tube, one (1)

•

12AT7 tube for reverb

Master volume

•

Treble, bass and mid controls for each channel

•

Tube reverb for luscious reverb tone faithful to Fender® Reverb amps. Tube reverb for the

•

crunch side as well but scaled back to recreate a typical Late 90's Marshall® head

Two switched outputs (CLEAN and CRUNCH) and one non-switched output. Non-switched output

•

sums both the clean and crunch channels

P a g e

Airspeed FM-50 Owner's Manual, Ver 2.0

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