Vectronics VEC-1680K - Manual (Page 19)

VEC-1680K Owner’s Manual Vacuum Tube Preamp
19
6. Connect an instrument to the Input jack of the preamp.
7. Connect a patch cord between the Output jack and your guitar amp.
8. Turn the preamp's Gain and Output controls off (counter-clockwise).
9. Make sure the preamp's power switch is On.
With the foot switch open, your guitar should bypass the preamp and play
through the power amplifier normally--as if patched directly in. With the foot
switch closed, the guitar signals should not reach the amp because both preamp
gain controls are fully down. If the relay fails to close, check the preamp's relay
circuit for errors.
If the relay circuit is working, check the operation of the preamp itself. With the
foot switch closed:
10. Set the preamp's Gain control at 12:00 (half open).
11. Slowly increase the Output control while plucking a note.
You should hear the guitar become progressively louder. Bring the Output
control up until the volume through the preamp roughly matches the volume
when in bypass mode setting. If strong hum or oscillation occurs, turn the
Output control down quickly and turn the preamp off. This indicates an
assembly problem in the preamp circuitry that needs correction. If the preamp is
operating correctly, you're done!