the noise stops.
Tip: If you think you have a microphonic tube, you can very gently tap on each tube with a pencil's
eraser to see if the sound becomes worse, stops, or changes. All tubes will amplify the sound of a
tap little, especially preamp tubes, but for example, if you hear an intermittent ringing sound and
tap each tube to find V7 (for example) is causing the ringing to start/stop, you can be sure it's the
problematic tube!
Changing Output Tubes:
V5, V6 (100 & 200W version only) and V7, V8 (see tube diagram on pg. 12)
In general, it's best to change all output tubes at once and preferable to buy a “burned-in”
matched set from a reputable dealer.
Output tubes can be replaced and biased by a qualified technician, however if you would like
to replace and bias the output tubes yourself, please see the detailed information about your
amp’s biasing system and bias procedure in the following sections.
Bias
Control
&
Test Points
Every Science Amplifier comes equipped with user-accessible bias test points and bias
control located on top of the chassis, adjacent to the output tubes. They can be accessed by
removing the rear panel of the amplifier.
Please see the diagram on pg. 12 to identify the controls and test points.
Bias Control: The bias control is a recessed slot adjustment (looks like a ¼” jack at first
glance), which can be adjusted with a normal flathead screwdriver.
Test Points (for use with standard multimeter probes):
•
Ground 1, Black: Plug in negative multimeter probe here while measuring bias
for V5 and V6.
•
V5, Red: Plug in positive multimeter probe to measure V5 output tube bias.
•
V6, Red: Plug in positive multimeter probe to measure V6 output tube bias.
•
Test points below are only fitted on 100W & 200W models:
•
Ground 2, Black: Plug in negative multimeter probe here to check bias for V7
and V8.
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