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4. Calibration
4. Calibration
4. Calibration
4. Calibration
Both the screen voltage and bias current of the output tubes can be calibrated using
the test points and control trimmers on the back panel of the amp. Calibration of both
screen voltage and bias current can be performed without removing the chassis from
the cabinet. Calibration is not terribly difficult. Once you have the tools you need and
have been through the process once or twice, you’ll find that you can do it in a matter of
minutes.
When & Why To Calibrate
When & Why To Calibrate
When & Why To Calibrate
When & Why To Calibrate
The Majesty is fully calibrated at the shop, so it is ready to play right out of the box.
However, calibration may become necessary in the future, so you should know about
what is needed, even if you intend to have the calibration performed by a technician or
guitar shop.
Screen Voltage
The screen grid supply voltage determines the operating point of the output tubes. The
Majesty provides you with the ability to measure and adjust the screen grid supply
voltage to help you tweak the amp for the sound and feel that you prefer.
The screen voltage is set at the shop to the voltage level I prefer. It’s a good idea to
check the screen voltage before setting the bias current, to ensure that it hasn’t drifted
from the value it was set at originally. You may also want to change the screen voltage
setting, to dial in a different feel and tone. Regardless, whenever you change the
screen voltage, you must set check and re-set the bias current after changing the
screen voltage.
Bias Current
The output tubes of the amplifier must draw a specific amount of plate current at idle
(with no signal going through the amp) in order for the amplifier to operate properly.
This current level is set with the Bias Adj control on the back panel of the amp.
Whenever you change output tubes, or adjust the screen voltage, you must calibrate the
bias current of the output tubes. This calibration procedure is explained in detail on
the following page.
Tools You Will Need
Tools You Will Need
Tools You Will Need
Tools You Will Need
Small Screwdriver
: you will need a small slotted screwdriver to make the
adjustments. The blade of the screwdriver should be around 1/8” wide. This is a very
small screwdriver, but not quite as small as a “jeweler’s” screwdriver (the type used to
fix eyeglasses).
Multimeter
: you will need a multimeter capable of measuring voltage in the 0-200mV
range, and also the 0-20V range. You do not need an expensive or complex meter.
Something like this will do just fine:
http://www.harborfreight.com/7-function-multimeter-98025.html#.Ux5GSoVMpB4