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
have their own typical effect on the sound. Even-order harmonics are neutralized, odd-order
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.