Reading
Room
Thermionic
Audio Books
Last Edited:
12-Sep-2004
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This is the DC Balance Adjustment procedure
for the 222D Integrated Stereo Amplifier, quoted directly from the H.H. Scott
"Service Bulletin."
"To make this adjustment a short audio cable with an audio (RCA
-phono) plug on one end and bare wires on the other end is needed.
Insert the
(RCA phono) plug into the RIGHT (B) Channel Tuner Input, and connect the two
bare wires to the LEFT (A) Channel Speaker Terminals (High and 0).
Connect a
loudspeaker to RIGHT (B) Channel Speaker Terminals (High and 0).
Connect the
Green wire that comes through the chassis grommet to the RIGHT (B) Channel
speaker impedance terminal which matches the impedance of the speaker being
used.
Remove V3 (ed note: the phase-splitter tube for the LEFT or A Channel).
Set the Controls as follows:
Input Selector |
Tuner |
Power Switch |
Off |
Stereo Selector |
Stereo |
Bass & Treble |
0 |
Stereo Balance |
0 |
Loudness Control (Vol pot) |
0 |
Compensator |
Loud |
Tape |
Out |
Scratch Filter |
Out |
Speakers |
On |
Equalization |
Either Position |
Insert the power line cord into an AC outlet and turn the unit on. Wait a
few minutes for the amplifier to completely warm up.
Slowly turn the Loudness
Control clockwise until you can just hear a low hum in the loudspeaker. (If
you turn the volume up too high, the amplifier will oscillate and produce a
motor-boating noise).
Take a small screwdriver and adjust the LEFT (A) Channel
DC balance control for minimum hum. (Hum is a 120 cycle low frequency noise --
do not confuse it with any high frequency noises present.)
Turn off the amplifier and replace the tube V3.
Connect the audio cable to
the RIGHT (B) Channel speaker terminals (High and 0) and insert the (RCA
phono) plug into the LEFT (A) Channel Tuner Input.
Connect the loudspeaker to
the LEFT (A) Channel Speaker Terminals (High and 0).
Connect the Red wire that
comes through the chassis grommet to the LEFT (A) Channel speaker impedance
terminal which matches the impedance of the speaker being used.
Remove V103
(ed note: the phase-splitter tube for the RIGHT or B Channel). Keep the
Controls the same as before.
Turn on the unit, and adjust the RIGHT (B)
Channel DC Balance control for minimum hum.
Turn off the amplifier and replace
the tube V103."
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