Owner`s manual

PAGE 4
INPUTS:
Located on the Rear Panel, these two 1/4” jacks are the Channel A and Channel B inputs for the 2:50. They are primarily
designed to handle the “line-level” signals from a preamp or an effects rack; but they are also sensitive enough to permit direct connection
of an instrument for test purposes, if needed.
The amplifier is stereo, offering two separate channels of amplification. If you wish to use only one
of its channels, it is necessary to: 1) Make sure a speaker (or load resistor) remains connected to
a speaker jack on both channels, including the unused one; or 2) Turn the VOLUME Control of the
unused channel to zero. (This is necessary because an amplifier channel receiving any amount of
signal at its input will require a “load” at its output -or else damage will most likely result.)
GROUND ISOLATION SWITCH:
This mini-rocker switch is extremely useful in reducing the hum and buzz caused by ground loops which
occur in rack installations. Ground loops occur when there is more than one path for grounds between electronic units. There are three main
type of ground loops; each one contributes its own trademark component of buzz or hum. The three types of ground loops are
1) Grounds being connected via the ground lugs of the power cords on the units. The rule-of-
thumb here is that one and only one unit in a rack should have a connection to the AC power
ground; all the other units in the rack should have their grounds lifted by using 3 to 2 adaptors on
their AC plugs.
2) Ground loops occurring because of two or more audio cables connecting two components.
The most common solution is to disconnect the shield from the sleeve connection at one end of some of the inter-connecting cables, so
that only one cable between each device has and intact ground shield. Some experimentation is required to find which cable is best for
conducting the ground, and which cables are best suited to have the special “clipped ground.” We recommend trying the intact-ground
cables for the signal path which flows, say, from an Effects Send jack to an effects unit; and trying the clipped-ground method on the cable
which connects the effects output back into an Effect Return.
3) Ground loops created by the physical contact between the metal chassis of the components and the steel rack rails. It is for this third
type of ground loop that the Ground Isolation switch was provided. This switch effectively lifts the electronic circuit ground from the metal
chassis ground (which otherwise must be done manually by disconnecting a wire inside of the amp.) Here again, the rule is that one
device in your system-and usually only one-needs its circuit ground connected to its metal chassis ground; all others should be lifted (in
other words, disconnected) for quietest operation. (Some effects units provide similar switches; some are constructed such that the input
ground and the output ground are permanently separated; in other cases, the method used to isolate the grounds is unclear.) Again, some
experimentation is vital to discovering which combination of “lifted” and “grounded” works best in your rack...and our Ground Isolation
switch makes this process much easier.
reAr PANeL CONTrOLS
4 OHM
8 OHM
INPUTS B
REAR VIEW:
2:50
F
U
S
E
F
U
S
E
INPUTS A
GROUND
SWITCH
LIFT
GROUND
BIAS
SWITCH
6L6
EL34
MUST MATCH TUBES SEE OWNERS BOOK
POWER FUSE
4A
SLO
BLO
120 V~
60 Hz
4 A
CHAN. B CHAN. A
8 OHM
4 OHM
SPEAKERS
SPEAKERS
WARNING: To reduce risk of fire or electric
shock, replace fuse with same type and
rating only. Do not expose this unit to
rain, moisture or thieves.
CAUTION: To reduce risk of fire or electric
shock, do not remove cover. No user-
serviceable parts inside. Refer all
servicing to qualified personnel.
4 OHM
8 OHM
INPUTS B
F
U
S
E
F
U
S
E
INPUTS A
GROUND
SWITCH
LIFT
GROUND
BIAS
SWITCH
6L6
EL34
MUST MATCH TUBES SEE OWNERS BOOK
POWER FUSE
4A
SLO
BLO
120 V~
60 Hz
4 A
CHAN. B CHAN. A
8 OHM
4 OHM
SPEAKERS
SPEAKERS
CAUTION: To reduce risk of fire or electric
shock, do not remove cover. No user-
serviceable parts inside. Refer all
servicing to qualified personnel.
WARNING: To reduce risk of fire or electric
shock, replace fuse with same type and
rating only. Do not expose this unit to
rain, moisture or thieves.
4 OHM
8 OHM
INPUTS B
F
U
S
E
F
U
S
E
INPUTS A
GROUND
SWITCH
LIFT
GROUND
BIAS
SWITCH
6L6
EL34
MUST MATCH TUBES SEE OWNERS BOOK
POWER FUSE
4A
SLO
BLO
120 V~
60 Hz
4 A
CHAN. B CHAN. A
8 OHM
4 OHM
SPEAKERS
SPEAKERS
CAUTION: To reduce risk of fire or electric
shock, do not remove cover. No user-
serviceable parts inside. Refer all
servicing to qualified personnel.
WARNING: To reduce risk of fire or electric
shock, replace fuse with same type and
rating only. Do not expose this unit to
rain, moisture or thieves.