Rocktron Vendetta, User Manual

Page: 12 / 16

- 12 -
Tube Replacement
POWER TUBE TEST POINTS USEAGE.
Please note that any adjustments, modifications, upgrades, etc
made to the VENDETTA may void the warranty. All work should be
performed by a qualified technician.
This feature on the rear panel provides a convenient point for measuring the idle current in the
power tubes without disassembling the unit. Different tube types can be installed and used in
the VENDETTA and biasing has been simplified. The instructions below explain how it works.
CAUTION!! DO NOT EXCEED THE VALUESSHOWN. This will shorten tube life, cause
possible tube failure and damage to the amplifier.
A digital voltmeter capable of displaying DC voltage from 0 to 200 millivolts is required. This can be an
inexpensive type found at most electronic suppliers such as Radio Shack. It is not necessary to connect
a speaker during this process.
1) Turn all controls full counter clockwise.
2) Turn the power on and allow 5 minutes for warm up.
3) Place the standby switch in the "on" position and allow another 5 minutes for the
tubes to stabilize.
4) You are now ready to measure. Set your voltmeter to the 200 millivolt scale. Insert the
black test probe into the "common" test point. Insert the red test probe into the #1 test point.
You should now see a reading within the range shown in the chart below.
While leaving the black probe connected, move the red probe to each of the four test points and
write down the voltage readings at each. You have now measured and documented the actual
current that is flowing through each of the four power tubes.
The readings should be within 5 millivolts of each other. If not, the tubes are not closely matched.
Now connect you meter to the rest point with the highest reading.
Turn the bias adjust with a small screw driver until the reading is within the value on the chart.
Tube Type Min Value Max Value
EL34 28mV 40mV
E34Ls 30mV 45mV
6L6 25mV 35mV
5881 25mV 35mV
KT66 25mV 35mV
6550 30mV 45mV
Note: 6V6 type is not safe to use due to the high (500 volts) plate voltage.