BIAS PROCEDURES
The Manley Euro Stereo 100 is a fixed bias system that requires very little attention. If you wish
to adjust or check the bias, follow the following steps.
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 probe
(red) into the black tip jack for the tube you wish to measure and the negative probe (black) in
the green (GROUND) tip jack and set the meter to read 'millivolts'.
2.
Each of the four (4) output tubes can have its own bias adjusted by altering its own bias
adjust pot. On diagram 2, you can see the numbering sequence for the 4 output tubes, the
corresponding tip jack (measurement point) and bias adjust pot.
3.
The first step to setting the bias is to turn on the amplifier and ensure that there is zero
signal input. Also, leave your loadspeakers 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.
5.
Place the probes 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
300 to 350 mV. Since you are measuring across a 10 ohm cathode resistor, this would
correspond to a 30 to 35 mA bias current.
6.
If you are unable to bring the bias voltage down to 300 to 350 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.
Whenever replacing an output tube, or when retubing the unit, use
tubes of the same type and quality as was fit by the factory. Watch and adjust the bias for the
specific output tube or tubes you are replacing as soon as you turn on the amplifier, then check
again after a half hour, and again in a few hours. Should you have any questions, or wish to
purchase approved tubes from us here at Manley Labs, please do not hestitate to call.
