6
Biasing power tubes & other technical info
High Internal voltages inside this amplifier can cause harm or Death!
Output tube Bias Setting:
Each tube is factory set for proper operation. The 6SN7 (4-watt version) is biased to 5 mv per
test point. There are 4 adjustments (one per tube) which should be set with a DC voltage
meter. The 20-Watt version uses 2 6V6 tubes, and each tube is set using its respective trimmer
to 20 millivolts (20-ma) per tube. EL-34’s in the 50 or 100-W version are set to 40 mv per tube.
There is one trimmer on the pc board for each tube bias. Bias is measured at the test points on
the board to ground and set to listed voltages. This should be set with the amp cold, then
reset after the amp has run for about an hour. Use a reliable digital voltmeter for these
settings.
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.
7
Warranty Information
The Fuchs Audio Technology-Amplifier Warranty
Fuchs Audio Technology
guarantees our products to be free from defective
workmanship or material failure for a
period of FIVE years (tubes excluded)from date of new
purchase to the original purchaser
. This does not apply to Fuchs amplifiers that have been
tampered with, damaged by shipping carriers, reverse engineered, or modified. Your warranty
form/information must be returned to Fuchs Audio Technology
within 30 days of purchase, or
your warranty will not be in effect. Fuchs Audio Technology
reserves the right to suspend or
terminate the above warranty at our sole discretion, should damage from any of the above
limitations and or exclusions be detected upon examination.
Keep the information on this page for your records.
Mantis Jr Manual Rev 1.0