6
TUBE AMP BASICS
Solid state amplifiers are really not much different from your standard
household electronics; you just plug them in and go. Tube amps, however,
are significantly different.
Tube amps carry significant voltage, even when turned off. DO NOT remove
the chassis from the cabinet unless you are a trained tech. The dangerous
voltages are a risk if you start messing with wires and transformers but is
perfectly safe to change your own tubes.
There is no set timeline for changing tubes. If you play every day, a good
rule of thumb is to replace your power tubes once a year and your preamp
tubes every other year. However, it is entirely possible for tubes,
particularly preamp tubes, to last decades.
Here are some signs that you need to change your tubes:
Excessive noise like squealing, humming, or hiss
Little or no high end/treble
Muddy low end or loss of clarity; amp sounds “muddy”
Mysterious fluctuations in the amp’s overall volume
There’s no sound from the amp!
“Biasing” is a technical term that has to do with things like “voltage applied
to the grid” and “moving the operating point into a more linear range.” If
you didn’t understand that, then don’t attempt this yourself.
JCA20HV is a Fixed-bias amp which allows you to “plug and play” EL84
power tubes without needing a bias adjustment.
SPEAKERS AND IMPEDANCE
