THD Electronics BiValve-30 User Manual

THD BIVALVE-30 INSTRUCTION MANUAL 1

THD BiValve - 3 0

In s t r u ctio n M a n u a l

Thank you for your purchase of the THD BiValve-30 amplifier! The big brother of the
THD UniValve, the BiValve-30 is a Single-Ended Class-A amplifier head with dual
output tubes that can be switched at will among many octal-based power tubes, including
6L6, EL-34, 6550, 6CA7. 6V6, 6K6, KT-90, KT-88, KT-77 and KT-66, for different
tones without re-biasing the amp. The two output tubes do not need to be matched in any
way—you are free to experiment with any combination you want! Likewise, the two
preamp tubes can be any combination of 12AX7, 12AT7, 12AU7, 12AY7 or 12AZ7. The
BiValve-30 delivers tones from smooth and clear to very aggressive overdrive, like the
UniValve, but with more power and a much more compliant output transformer for
thicker lows. It is easily capable of driving a 4x12" cabinet, yet quite small and relatively
light. Finally, it has a built-in Hot Plate® Power Attenuator that allows for full output
distortion at almost any volume. The unique combination of our touch-sensitive input
circuit and the wonderfully active and reactive tone control section (that we slaved a year
to perfect) make for a front-end that really responds to subtle and not-so-subtle changes
in the signal being fed into the amplifier either by the guitar or any effect that may be
between the guitar and the amplifier.

THD BIVALVE-30 INSTRUCTION MANUAL 2

THD BIVALVE-30 INSTRUCTION MANUAL 3

TABL E O F C O NT EN T S

Instruction Manual .................................................................................................. 1

What Does “Class-A” Mean? ....................................................................................... 3

BiValve-30 Controls...................................................................................................... 4

Front Panel.................................................................................................................. 4

Back Panel .................................................................................................................. 6

Switching Tubes in the BiValve-30............................................................................... 7

Power Tubes ............................................................................................................... 7

Preamp Tubes ............................................................................................................. 7

THD Electronics Contact Information......................................................................... 8

What Does “Class-A” Mean?

At the beginning of this manual, we explained that the BiValve-30 is a “Single-Ended
Class-A” amplifier—but what does that mean? “Class-A” is a term given to an amp that
runs its tubes at full current all the time, unlike most tube amps that alternate between
running one set of tubes and the other set, each for one half of the wave. The set not in
use is turned off by a positive swing of the grid voltage. Single-ended out-put stages
always operate in Class-A. Most guitar amplifiers over 5 watts operate in Class-AB
Push-Pull. The upshot is that Class-A operation has its own unique tone characteristics
that set it apart from other tube amp classes. Class-A amps sound great at low volumes,
and even better as you turn them up. There is no point at which you will be waiting for
the tube to receive its full current for the best sound—it always will.