12
Screen Voltage
Screen Voltage
Screen Voltage
Screen Voltage
Procedure:
1. Power up the amp as usual.
2. Attach the meter as shown in the diagram above. Set the meter to read DC
voltage in the 0-20V range.
3. Insert the screwdriver into the hole shown, and make sure that it properly mates
with the adjuster screw of the trimmer pot. Adjust the trimmer pot until the
meter shows the correct value. This is a 10-turn trimmer pot, so you may have
to rotate it through several turns to arrive at the value desired.
4. As soon as you reach the target value, switch the amp to Standby mode, set up
the meter to perform a bias test, then switch to Operate mode and re-set the
bias current (as described in the previous section).
Target Value (as read on the meter connected as shown above):
2.08V
Technical Details:
The voltage you measure at the Screen Voltage test points is 1/100 of the actual screen
voltage supplied to the output tubes. Thus, if you measure 2.08V at the test points,
the screen grid voltage supplied to the output tubes is actually 208V. This voltage
division was done for safety reasons.
I prefer to set the screen voltage to 208V (which is a reading of 2.08V on the meter) –
it’s a “sweet spot” where the attack, feel, and harmonic content are ideal for my taste.
However, you may wish to use a different setting for a different sound and feel.
Higher screen voltage will give you a “harder” feel and a “sharper” attack. Lower
screen voltage will result in smoother overdrive and a softer feel.
