Sonic Frontiers SFS-40 Owners manual

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 essen­tial, 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 slot­ted 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.

OPERATION

1. Connect your speaker leads and input cable on the amplifier, making sure the power
switch is in the “OFF” position (down).

2. Using a long-handled slotted screwdriver, rotate all of the adjustment controls fully
counter-clockwise.

3. Turn “ON” the amplifier. After approximately 5 seconds you should see an orange glow
appearing inside each tube. Wait one minute, then turn the selector switch knob on the top surface
of the chassis to the far left position (fully counter-clockwise). Now insert a flat bladed screwdriver
into the front left bias control slot and slowly rotate the control clockwise while observing the front
panel bias meter. Adjust the control until the meter pointer reads “40” on the meter scale. Now
rotate the selector knob clockwise to the next position and adjust the left rear bias control for a “40”
reading on the meter. Continue the same procedure for the remaining two output tubes, rotating
the control clockwise. When you have adjusted all four tubes to the “40” position, return the selec­tor knob to the middle “12 o’clock” position (the indicator mark on the knob should be pointing
straight towards the back of the amp.) The first time you use the amplifier, you should recheck the
bias settings on each output tube after about 30 minutes of use (when checking, please ensure
that there is no signal going through the amp). Adjust if necessary. Periodic checking is needed for
all future use.

Your SFS-40 amplifier is now ready for use.

NOTE: The “40” position on the meter scale biases each output tube for maximum sonic

performance and longest tube life. The red mark on the meter scale at the “50”
position indicates the absolute maximum that the EL34 type tube should be run at
(running this tube type at “50” will drastically shorten the life of the tube without any
redeeming sonic advantages). The “50” position can be used, however, if 6550(a),
KT88 or KT90/KT99(a) type tubes are installed.

CLEANING

The beautiful stainless steel (non-magnetic) finish of the chassis and transformer top covers will last
for years. A regular dusting with a soft, non-abrasive cloth will generally keep the finish looking like
new. Fingerprints may be removed with a small amount of silicon spray, such as WD-40 TM. Be
sure to apply any liquid into a soft cleaning cloth, not directly onto the chassis. At no time should
you allow any liquids to drop onto the amplifiers; it may run into the electronic circuitry underneath
and cause damage which will not be covered under your warranty!