Sonic Frontiers SFM-160 Owners manual

SFM-75 MK II PRIV ATE

MONO TUBE AMPLIFIER

OPERATING MANUAL

We at Sonic Frontiers are sure that you will derive many years of listening pleasure with your new
SFM-75 MKII mono tube amplifiers. This brief operating manual contains important information
regarding the operation and care of the amplifiers, so be sure to read this manual carefully and fol­low these simple instructions in order to keep them looking, operating and sounding their 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.

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 SFM-75 MKII amplifiers are 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 35% to
50 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 SFM-75 MKII ampli­fiers.

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 clockwise.

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 counter-clockwise. Adjust the control until the
pointer indicates “50” on the dial. Now rotate the selector switch to the “V4” position and rotate the
V4 bias control counter-clockwise to set the meter pointer at “50.” Wait a few minutes and recheck
the settings for both tubes.

Once you have finished adjusting both bias controls, return the selector switch to the “OFF”

(centre) position.
Your SFM-75 amplifiers are 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 “Trouble­Shooting” 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!

TROUBLE-SHOOTING GUIDE

If at any time your SFM-75 amplifiers fail to work, follow this simple checklist:

1. Make certain that the A.C. power cord is plugged in firmly, both at the A.C. wall socket and at the
A.C. amplifier socket.

2. Remove the A.C. power cord at the amplifier and open the fuse hatch on the A.C. input
socket. Check that:

A. A “slo-blo” fuse, with a rating of 2 l/2 amps 250V, is installed (or l.25 Amp 250V. for