SFS-40 PRIV ATE
STEREO TUBE AMPLIFIER
OPERATING MANUAL
We at Sonic Frontiers are sure that you will derive many years of listening pleasure with your new
SFS-40 Stereo Tube Amplifier. This brief operating manual contains important information regarding
the operation and care of the amplifier, so be sure to read this manual carefully and follow these
simple instructions in order to keep it looking, operating and sounding its best!
VACUUM TUBES
Handling
We suggest that you do not handle the large power tubes with your bare hands or fingers as skin
oils deposited on the glass surface can “leach” through the glass envelope and cause the tube to
become “gassy.” In other words, your tube life may be shortened unnecessarily. Use a paper towel
or one of the cotton gloves (supplied) instead. This is also the recommended procedure for handling
the small input tubes. Also, check to be sure that none of the 6DJ8 tube pins are bent when you
install them.
Installation
Whenever you remove or insert the input or power tubes into their sockets, handle them gently and
do not force them into the sockets. Instead, “rock” them slightly as you slowly push them into place,
making sure that they are properly seated. Over-enthusiastic “rocking” may snap-off the moulded
keying lug (orientation pin) at the base of the tube (not covered under warranty)!
Recommended Tube Types
Your SFS-40 amplifier is supplied from the factory with 6DJ8 tubes for the input and driver stages
(installed into the small sockets). You may also use tubes of the following designations: ECC88,
6922, or 7308/E188CC.
The power tubes are factory supplied matched pair EL34 (mil-spec, sometimes called E34L’s) type
but you may also use E34L’s, 6CA7’s or 6550/6550A/KT88/KT90/KT99a types. Although not essen-
tial, we recommend the use of matched pairs of power output tubes for lowest distortion.
Tube Biasing
This is a simple yet important function of the front panel meter, the selector switch and the four slot-
ted adjustment controls protruding above the top surface of the chassis.
It is essential that the following procedures be followed before you turn on your SFS-40 amplifier.
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