3rd Power Kitchen Sink 6VEL User Manual page 16

Power Tube Biasing:
CAUTION:
NEVER touch hot tubes!!! Temperatures can exceed 500˚F and cause severe burns!
Biasing your tube amplifier need not be a scary endeavor as the process is pretty straightforward.
Heed all warnings, cautions and instructions and you should do fine. If you're unsure or unclear on
the process, do not attempt to manipulate the bias from factory settings. If, during the biasing
process, you hear a loud "pop" or see a tube "flash" immediately power down the unit and seek a
qualified tube amplifier repair/service technician.
CAUTION:
DO NOT attempt to load a rectifier tube in a power socket and vice-versa!!!
The Kitchen Sink 6VEL has a logical tube layout with the audio and power tubes located in a cluster
near the back corner (see page 19). The rectifier tube is isolated and located in a corner on the
opposite end of the chassis. Take care to only install proper tubes in the correct locations. Not
doing so will damage your amplifier and could void your warranty.
OPERATION NOTES:
• Monitor your output tube bias at idle current. To achieve idle current, your amp must be turned
on and operating at idle (no audio signal being fed into the input or the FX loop return). Make
sure that your speaker is plugged in.
• Attach the negative test lead from your multimeter to the GND- terminal (black) on the back
panel of the amp.
• One at a time, attach the red (positive) test lead from your multimeter to either V8+ or V9+
terminals (red) and note the reading on your meter. Then read the voltage on the other tube.
The resulting numbers should be within 6mv of each other. Note that your maximum bias
setting must be based off of the higher number.
• To optimize your output tube bias, adjust the control screw by inserting a mini flathead screw
driver into control port (see diagram and description for item number (28)). Turn clockwise to
bias your tubes 'hotter' (increasing the idle current) and counter-clockwise to bias your tubes
' c ooler' (decreasing the idle current).
• Cooler settings (lower idle current) can increase the life of your tubes. Too cool and the sound
will tend to be brash and one dimensional.
• Optimal tone and feel can be found when the bias range is around 50% - 70% of your tube's
maximum operating range. This will vary between the types of tubes you choose to operate
your amp with.
16