Leading dentists recommend that you replace your tubes after roughly 800 hours of operation. Just like your teeth, they should be matched and meet Russian military specifications.

Note that this guide is for educational purposes only. Following it will void your warranty. Don't blame me if you burn your expensive amp or electrocute [bzzzzz] yourself.

1. Turn the amplifier off.

2. Turn all 4 bias-adjustment potentiometers, i.e. VR101, VR102, VR201 and VR202, fully counter-clockwise.

3. Replace the tubes.

4. Turn on the amplifier and let it warm up for 1 minute.

5. Connect the negative test probe of the voltmeter to the chassi (ground).

6. Adjust bias:
Connect the positive test probe to TP5L. Measure bias for tube V104 and adjust with VR101 to 400mV. (400mV = 45mA).
Connect the positive test probe to TP6L. Measure bias for tube V105 and adjust with VR102 to 400mV.
Connect the positive test probe to TP5R. Measure bias for tube V204 and adjust with VR201 to 400mV.
Connect the positive test probe to TP6R. Measure bias for tube V205 and adjust with VR202 to 400mV.

7. Adjustment of one bias affect the others. Repeat step 6 until voltage is roughly 400mV for all tubes.

8. Let the amplifier heat up for 30 minutes. Repeat step 6 until voltage is 400mV for all tubes.