THD Electronics BiValve-30 - Manual (Page 7)

THD BIVALVE-30 INSTRUCTION MANUAL 7
Filament Fuse: This fuse is for the low voltage supply that drives the filament or heater
supply for the tubes. Disconnect the power cord before replacing. Replace only with a
fuse of the same type and rating.
HT Fuse: The high-tension fuse is for the high voltage supply that feeds the plates of the
tubes. Disconnect the power cord before replacing this fuse. Replace it only with a fuse
of the same type and rating.
IEC Power Cable jack: Use a standard universal VAC power cable with your BiValve-
30.
Mains Fuse: The mains fuse protects the amplifier from damage caused by power tube
failure or a failed component in the power supply. If it blows, it must be replaced with a
fuse of the same type and rating.
Switching Tubes in the BiValve-30
Power Tubes
The BiValve-30 is a “self-biasing” amplifier. What that means is that the BiValve-30’s
circuitry senses the current needs of the output tube and provides the correct bias voltage
to the cathode of the output tube regardless of tube type or wear. In other words, without
any trip to an amp technician, you can simply replace either or both of its output tubes
with tubes that have different sound characteristics. For example, a 6550 will stay
cleaner at higher volumes, but when overdriven, has an astoundingly "woody" character.
On the other hand, an EL-34 will break up earlier than a 6550 and gives a more "British"
sound. The ever-popular 6L6 family of tubes gives a tight overdrive with less power than
a 6550 but more detail than an EL-34. You can also combine tubes of different types, so
you could try one 6550 and one EL-34 tube, for a unique sound incorporating
characteristics of both tube types! Even within the same type of output tube there are
"harder" and "softer" tubes, so two guitarists playing with the same guitar through the
same BiValve-30, but simply switching the tubes to their preference, can have noticeably
different tones.
NOTE: If you want to use an EL-84 power tube, you will need to use the THD YJUni
Adapter, which is specially designed to allow you to use EL-84 tubes in a self-biasing,
Class-A amplifier like the UniValve or BiValve-30.
Preamp Tubes
You can experiment with preamp tubes in the BiValve-30 as easily as power tubes—just
pull out the current tubes and inset a new one! The UniValve can take any type of dual-