Clean Machine-Manual Rev. 1.1 08-2011
7
Biasing power tubes and other technical info
Biasing and Internal Adjustments:
Part of chassis and circuit board is shown below with the chassis sitting on its
transformers, and front panel facing you. There are exposed high-voltages in this
chassis, even with the amplifier shut-off! If you are not familiar with tube
amplifiers and/or high voltages, do not attempt to remove the chassis from its
cabinet or to attempt to service this amplifier. Refer servicing to the factory or to
someone with experience servicing these types of amplifiers.
High Internal voltages inside this amplifier can cause harm or Death!
AC Balance:
This is factory set for linear clipping at maximum power output, and is set with an
oscilloscope for proper adjustment.
Bias Controls:
The tube (in the 75) or each pair of tubes in the 100 and 150-W models is factory set
for proper bias. measured on the one-ohm cathode resistor connected to each power
tube pin 8. This should be set with the amp cold, then reset after the amp has run
for about an hour. Use a reliable digital volt meter for these settings. The 75 and 150
(using 6550 tubes) are set to .040 volts (40 millivolts dc = 40 ma) per tube, and the
100 (using 6L6’s) should be set to .036 volts (36 millivolts dc= 36 MA).
DISCLAIMER: There are exposed Internal high-voltages in this amplifier. Do not
attempt to service, repair or conduct tube biasing unless you are qualified to do so.
Please contact Fuchs Audio beforehand with questions in this regard. Fuchs Audio
takes no responsibility or shall be held liable for any personal harm caused or
damage to this amplifier as a result of unauthorized service, repair or internal
adjustments made to this amplifier
.