USER MANUAL
Hughes & Kettner
VS 250
Stereo Tube Power Amplifier
Hughes & Kettner
Stereo Tube Power Amplifier
Congratulations!
You have just acquired a highquality sound tool which combines the sonic superiority of
vacuum tubes with the optimum usefulenss of a guitar rack. The VS 250 incorporates the
sum of our experience with vacuum tubes. May you enjoy the new measure of expressiveness
and creative freedom it affords.
The following operating instructions delve into the special features and capabilities of the
VS 250 in detail.
The Hughes
&
Kettner VS 250 is a twochannel tube power amplifier. As with all tube
devices, there are a few things you should pay special attention to:
For this reason a tube device needs a
Tubes require a specific operating temperature.
moment after power-up (depending on the operating environment about 20 seconds or SO)
until it is completely ready for operation.
Tubes are sensitive to being jostled or shaken when hot. After use, allow the unit to cool
down for a few minutes before transporting it. Avoid subjecting it to strong vibrations while in
operation.
A tube amplifier should never be operated without a load (speaker) connected to it.
Make sure that the vents in the front and back of the unit remain
Tubes produce heat.
unobstructed.
CONTROLS
The VS 250 has two independent channels, identical to each other. The controls for each
channel are likewise identical; so what is said below about channel A also holds true for
channel B.
FRONT
Stand by
There are two different levels of voltage controlling the tubes:
1) the basic voltage intended to warm the tube to minimum operational temperature. This
voltage is always applied to the tube whenever the power switch is in the on position.
2) the operating voltage (plate voltage) which drives the tube. The operating voltage is turned
off with the STANDBY switch.
The green LED indicates the unit is in standby mode, the red LED above the STANDBY switch
indicates normal playing mode.
If you are using only one channel of the
switch the other channel into standby mode.
Volume
VOLUME controls how much the input signal is amplified, thereby controlling the output
volume of the channel. Due to the special LINE DRIVER circuitry in each channel’s input,
VOLUME offers a very wide range of control which also accommodates devices with very low
output levels (300 mV are perfectly adequate to drive the output stage; voltages up to 10 volts
can be accepted without overloading the input).
Presence
With tube amplification, the higher frequencies (PRESENCE) are most effectively controlled at
the power amp stage. This frequency range plays a major role in determining the character of
the guitar sound and its ability to cut through.
a
The intensity of the PRESENCE control depends to a great degree on the guitar sound itself:
heavily overdriven sound with a great deal of overtone energy will respond to the PRESENCE
control much more dramatically than will a clean sound with little overtone content.
Over the last 30 years of tube amp tradition, two different types of PRESENCE control have
established themselves as standard:
the
"
British” type, which only affects higher frequencies, and only boosts, and
the “American” type, which affects a broader range of frequencies from high mids to
harmonic overtones, and can either boost or cut.
Since both PRESENCE philosophies make sense, and both allow for very different characters,
particularly with overdriven sounds, the VS 250 offers both types.
The signal is unaffected when the control is in the
PRESENCE 1 is the “American” type.
3-o'clock" position.
"
in the fully counterclockwise position, the sound is
PRESENCE 2 is the
unaffected.
"
British” type.
With the SELECT switch you can alternate between PRESENCE 1 and PRESENCE 2. The
triangular-shaped LEDs indicate which presence control is currently active. On the back of
the
there is one l/4” jack per channel for connecting a footswitch to select between
PRESENCE 1 and PRESENCE 2.
Please note: The PRESENCE controls do not affect the tone as strongly in TRIODE mode than
in PENTODE mode!
Mains
Mains is the power switch of the VS 250. When the unit is powered up, the red LED above
It is good practice to switch each channel of the VS 250 to STANDBY
this switch will be on.
both before powering up and before switching off.
BACK
Power Cord J ack
If you are on tour in
This jack accepts the 110/120-volt power cord supplied with your unit.
Europe, this jack will accept a 220/240-volt power cord. (See “Main Fuse” and “Voltage
Selector” below.)
Main Fuse
For overseas use, change the fuse to match local voltage:
220/240 Volts -AT 2 1/2 Amp
110/120 Volts Slo-Blo5amp
-
Voltage Selector
USA 110/120 volts
-
European continent and Great Britain
-
220/240 volts
Anode Fuse
Operating voltage of the tubes, fused separately for each channel.
Fuse rating: Slo-Blo 0.315 Amp or Slo-Blo 1/2 Amp
Pentode/Triode
The first guitar tube amps from the 30’s and 40’s utilized TREIODE power amp tubes. Since
triodes tend to emphasize even-order harmonics, these amps had a very typical sound with a
warm even tone, even when overdriven. Great for sweet, warm, full, fat blues.
To obtain higher power levels, tubes were developed in the 50’s with 5 electrodes
(PENTODES), and these have since become standard in all tube amplifiers. PENTODES likewise
Even-order harmonics are neutralized, odd-order
have their own typical effect on the sound.
harmonics stand out. This adds richness to the character of the sound, but also makes it
rougher, with an “edge”, lending itself spectacularly to rock-oriented music.
Each of the two channels of the VS 250 can be switched separately from PENTODE to
TRIODE mode. The power in triode mode is reduced to 25 watts RMS per channel; the sound
character changes as described above.
Please remember: for technical reasons, the effect of the presence control will be much more
noticeable in pentode mode than in triode mode, and will be more noticeable the more
overdriven a guitar sound you use!
Presence Select Footswitch
Connect a commonly available on/off footswitch to this jack, and you can alternate between
PRESENCE 1 and PRESENCE 2. If only one footswitch is connected, both channels will be
switched simultaneously.
Ventilation
Heat generated by the tubes in the VS 250 is transferred to a heat exchanger, which is cooled
in turn by an extremely low-noise fan.
This design prevents excessive heat build-up in the
housing, and ensures even cooling of the tubes. Please see to it that the ventilation slots on
both the front and the back of the VS 250 are not blocked.
Circuitry in the power amp stage constantly monitors the internal temperature. In the event of
overheating(caused, for example, by blockage of the vents), the VS 250 will automatically
shut down and thereby prevent any damage to itself.
Inputs
Each channel of the VS 250 has two parallel inputs. The LINE OUTS of a guitar preamp (or
effect unit) are to be connected here, one to each channel. The purpose of the parallel inputs
is. to allow for input bridging. You could, for example, connect a cable from the second,
parallel input jack of one channel to another power amp; or from Channel A of the VS 250 to
its own Channel B, thereby using the VS 250 as a 2x50-watt mono power amp.
Speaker Outputs
Each channel of the
250 has three speaker output jacks with different impedances: 4
ohms, 8 ohms, and 16 ohms. Use the jack which corresponds to the impedance of the guitar
loudspeaker cabinet which you are using. All three jacks may be used simultaneously.
If you wish to connect two &ohm cabinets to one channel, please connect one of the cabinets
If you wish to
to the 4-ohm input, and connect the second cabinet to the first in parallel.
connect two 16-ohm cabinets to one channel, please connect one of the cabinets to the 8-ohm
input, and connect the second cabinet to the first in parallel.
Technical Specifications
Tubes, each channel:
Driver stage: 1 x ECC 83 (or 12ax7 or 7025)
1 x ECC 82 (or 12AU7
Power stage: 4 x EL 84
Output per channel:
Pentode mode: 50 watts RMS
Triode mode: 25 watts RMS
Input sensitivity:
300 mV to 10 volts
Presence control per channel:
PRESENCE 1
PRESENCE 2
:
4
dB
@
4000 Hz, broadband
:
+2 dB @ 6000 Hz, broadband
Loudspeaker jacks per channel:
16 ohms; all usable simultaneously
4
/
8
/
Cooling:
Temperaturecontrol-circuitry, heat exchanger, and Papst fan
Thermal protection, automatic shut-off
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