THD Electronics UniValve - Manual (Page 7)

THD UNIVALVE INSTRUCTION MANUAL 7
Switching Tubes in the UniValve
Power Tubes
The UniValve is a “self-biasing” amplifier. What that means is that the UniValve’s
circuitry senses the current needs of the output tube and provides the correct bias volt-age
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 the output tube with one that has
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. 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 UniValve, 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.
Preamp Tubes
You can experiment with preamp tubes in the UniValve as easily as power tubes—just
pull out the current tubes and inset a new one! The UniValve can take any type of dual
triode preamp tube, such as 12AX7, 12AY7, 12AU7, 12AT7, 12AZ7, 12DW7, 12BH7,
ECC83, ECC82, ECC81 and more. You can try any of the above tube types in any
combination—remember, experimentation is the name of the game!