4.2 Pre-amp Tubes
The pre-amps are equipped with 12AX7 tubes in all positions. The pre-amp
tubes are not used to make big power, but merely as pre-amplifiers. Therefore
their life expectancy is much higher than that of the power amplifier tubes.
This is not to undermine their utter importance in overall sound and response of
the amplifier. Also, many nuisance defects like crackling noises and low dynamics
are directly related to defective pre-amp tubes. Like all other tubes, 12AX7 tubes
come in many different gain stages, and offer a wide variety of tonal behavior.
Our choice for production was made to ensure a wide variety of tones, with low
noise and, hopefully, excellent reliability.
4.3 Microphonics and Bad Noises
The overall performance of pre-amp tubes is easily influenced by mechanical
factors from the outside. This would manifest itself by a sudden feedback sound
with high pitch. The input stage is especially suspect to this phenomenon. If one
encounters microphonic tube behavior, then the first tube should be checked as a
rule. Pre-Amplifier tubes can also cause hum or other bad noises, like crackling or
ticking.
