Octave V 70 SE [19/33] V 1 v 2 v 3 v 4

7. TUBES

7.3. THE BIAS MEASUREMENT SYSTEM

The BIAS measurement facility makes it easy for you to check and adjust the idle current of the

output tubes. Getting the BIAS setting right for all four tubes is critical for both the sound of the

power amplifier section and for the service life of the tubes. This feature guarantees consistent

sound quality over the entire lifetime of the output tubes.

That is why we have built this BIAS measurement facility into the V 70 SE – to allow you, the user,

to carry out the adjustment yourself without the need for test equipment. The use of precision op

amps makes it possible for you to set the BIAS to an accuracy within 0.3%, making it superior to

any other method.

Using selected output tubes only makes sense if the idle current is adjusted accurately, as is

clearly shown in Fig. 1 Technical Data.

V 1 V 2

V 3

V 4

Regler für Röhre

V1 V2

rot

grün gelb

How to set the BIAS

Turn the Input selector knob [2] clockwise to the BIAS position to activate the measurement

circuit.(pos. 6); Signal/input selection is disabled. The 3 LEDs above each screw in the display

panel show whether the BIAS setting is too low, correct, or too high. Use the small screwdriver

supplied to adjust the BIAS.

To increase the BIAS current to each output tube, turn the screwdriver clockwise.

The adjusting screws are fully insulated. There is no risk of electric shock and the adjustment

procedure is completely safe.

The LED display:

Red LED only Setting is too high

Green + red LED Setting is OK for KT 88 6550, etc. = high BIAS

Green LED only Setting is OK.

Yellow + green LED Setting is OK for EL 34, 6L6, KT 66, etc. = low BIAS

Yellow LED Setting is too low