Sonic Frontiers SFS-50 Owners manual
SFS-50 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-50 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.
Recommended Tube Types
Your SFS-50 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/E88CC.
The power tubes are factory supplied matched pair KT88’s but you may also use 6550/6550A types.
EL34/6CA7 tubes may also be used but the available output power will be reduced by about 30% to
35 watts. 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 two 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-50 amplifier.
OPERATION
1. Connect your speaker leads, input cable and power cord to each amplifier, making sure the power
switch is in the “OFF” position (down).
2. Using a long-handled slotted screwdriver, rotate both of the adjustment controls fully counterclockwise.
3. Turn “ON” the amplifiers. After approximately 5 seconds you should see an orange glow appearing inside each tube. Wait one minute, then turn the selector switch to the “V3” position marked on
the chassis. Insert the screwdriver into the corresponding bias control and watch the meter pointer
as you slowly rotate your screwdriver clockwise. Adjust the control until the pointer indicates “50” on
the meter. Now rotate the selector switch to the “V4” position and rotate the V4 bias control clockwise to set the meter pointer at “50.” Follow the same procedures for LV3 and LV4. Wait a few minutes and recheck the settings for all 4 output tubes.
Once you have finished adjusting all 4 bias controls, return the selector switch to the “OFF”
(centre) position.
Your SFS-50 amplifier is now ready for use.
NOTE:The red mark at the “60” point on the meter scale is the maximum recommended bias point for
the 6550/KT88 output tubes. Setting the bias meter to read in excess of this value will exceed the
rated dissipation rating of the tubes and unnecessarily shorten your tube life with no redeeming sonic
benefit. You may, if you wish, operate the tubes at the “40” mark for somewhat longer tube life. If you
are unable to perform the previous adjustments, turn to the “Trouble-Shooting” section of this manual
on Page 3.
CLEANING
The beautiful satin chrome 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 window cleaner, such as Windex 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!
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