5.2 Power Amplifier Tubes
5.2.1 Function
As the name suggests, the power amp section is the part of the
amplifier that produces output power, measured in watts. Preamp
signals are sent to the power amp(s), which amplifies this signal to a
level that is acceptable for loudspeakers. Guitar amplifiers utilize
several different types of power amps, which differ in output power
and tone. We chose the tube type power amplifier for its tried-
andtrue performance and familiar tonal behavior.
5.2.2 Selection
Diezel Co. installs the most reliable and best sounding tubes that are
currently available in sufficient quantities. So it is possible that tube
brand and tube type will change during production. You can fine-tune
your Herbert by having different type and brands of tubes installed,
however, it is imperative that the amp is biased properly. Herbert
utilizes 6 power tubes, organized in 3 pairs with triple bias possibility.
This allows use of 3 different pairs of power tubes, either the same or
different types. Yes, this means that you can mix 6550’s with EL34’s, or
6L6’s with KT88’s etc. Cool, no?
A quick and general overview of the most common tube types for
use in the Herbert:
EL34/6CA7:
Aggressive, slender low end, higher total harmonic
distortion… Recommended bias setting: 60-70mA
(pair)
6550:
Very loud, very good dynamics, strong low end,
amazingly percussive… Recommended bias: 100mA
(pair)
