Manley 100/200 WATT MONOBLOCK AMPLIFIER - Manual (Page 7)

BIAS PROCEDURES
The Manley Euro 100/200 Monoblock Amplifiers uses a fixed bias system that requires very
little attention. If you wish to adjust or check the bias, follow the following steps.
For this procedure you will need a voltmeter (a hand held autoranging DMM digital
multimeter is the easiest) and a small flat screwdriver.
1. On diagram 2, which depicts the top panel of the amplifier, you can see 4 black tip
jacks and 1 green tip jack. To measure the current draw of each output tube place the
positive meter probe (red) into the black tip jack for the tube you wish to measure and the
negative meter probe (black) in the green (GROUND) tip jack and set the meter to read
'millivolts'.
2. Each of the eight (8) output tubes can have its own bias adjusted by adjusting its own
bias adjust pot. On diagram 2, you can see the numbering sequence for the 8 output tubes,
the corresponding tip jack (measurement point) and bias adjust pot. Everything reads left to
right.
3. The first step to setting the bias is to turn on the amplifier and ensure that there is
zero signal input, either leave the preamplifier or source signal turned off or unplug the
amplifier input. Also, leave your loudspeakers connected as these provide an ideal load on
the output. It is recommended that you leave the amplifier on long enough to ensure that the
tubes have reached their stable current draw, at least 1/2 hour is recommended.
5. Place the red meter positive probe in the first black tip jack (negative probes remains
in the green tip jack for whole biasing proceedure) and adjust the first bias trip pot (see
diagram 2) until you measure 260mV to 275 mV. Since you are measuring across a 10 ohm
cathode resistor, this would correspond to a 26 to 27 mA bias current by Ohm's law.
6. If you are unable to bring the bias voltage down to 260 to 275 mV on any tube then
we recommend that the tube be carefully watched or replaced.
7. Follow step five with the remaining tubes. Once they are all set, your amplifier
should be in perfect operation.