Randall Amplifiers NB KING100 - Manual (Page 7)

REAR PANEL FEATURES
MIDI IMPLEMENTATION - cont
Control Change #56 (w/control Value 127) allows for Instant Access selection of Channel 1.
Control Change #57 (w/control Value 127) allows for Instant Access selection of Channel 2.
Control Change #58 (w/control Value 127) allows for Instant Access selection of Channel 3.
The first valid MIDI message (Program Change or Control Change) that the EMB board
receives will determine how it repsonds to subsequent MIDI messages. For example;
(A) if the first MIDI message the EMB board receives is the Program Change, then it will
ONLY respond to Program Changes and all Control Change messages will be ignored.
(B) if the first MIDI message the EMB board receives is a Control Change, then it will ONLY
respond to Control Changes and all Program Change messages will be ignored.
POWER TUBE BIAS SECTION
You will need a decent quality digital voltmeter capable of measuring in the 100mVDC
range. This is a basic type of meter available at any electronic supply company or Radio
Shack. Typical cost will be $15-$30 or about the cost of one bias adjustment from your
local amp technician. You will also need a small flat blade screwdriver to turn the
adjustment control.
To check and/or adjust the bias, turn both the Power and Standby to the ON position and
all knobs all the way down. Turn the meter on and set for reading DC millivolts. Insert
the Black (Negative) meter lead into the panel hole label “COM” or Common. Insert the
Red (Positive) meter lead into either panel hole marked TEST POINT. With your screwdriver
turn the BIAS ADJUST control to obtain a recommended reading of 80mVDC. Now place the
red meter lead into the other BIAS ADJUST and also set to 80mVDC. On this amplifier you
are adjusting a pair of tubes at one time, so 80 millivolts DC is the standard factory setting
for each pair, but adjust the bias range from 70 - 90mVDC if desired for a certain sound.
A lower bias setting will increase the life of your tubes, but produce a softer more bottom
heavy feel. A higher bias setting will decrease the life of your tubes, but produce a more
compressed harder tone and feel. If replacement tubes are needed you will need to
purchase the tubes in matched pairs. This amplifier will accept any EL34 or 6L6 type of
power tube and the bias setting for either type will be the same.
EFFECTS LOOP