DIY - Tweakin' Your Tube Amp
Ask just about any guitarist out there whether they prefer a tube or a solid
state amplifier, and you'll no doubt get a unanimous result: "TUBE".
Tubes, being the primitive devices they are, are prone to differences from
manufacturer to manufacturer, etc. Experimenting with different tubes can be an
easy and inexpensive way to tweak with your amp's tone and learn a lot about how
these little bottles of light do the magic they do.
First, and most importantly, tube amps operate at VERY HIGH VOLTAGES, enough
to KILL YOU, in fact. I don't recommend dying in pursuit of the perfect tone, so
be VERY careful when swapping tubes. Start small - literally. Start with the
pre-amp tubes, the smaller tubes found closest to the amps guitar input jacks.
The larger tubes are usually the power tubes and if your amp has one, a tube
rectifier. This is where you get into some dangerous territory, voltage-wise.
We'll save talking about power & rectifier tubes for another more in-depth
guide, and just focus on the pre-amp tubes for now. Most amps have a chart
inside of the cabinet showing the type and location of the tubes. Those tubes
labeled as 12AX7, 12AT7 (any 12Axx), ECC83 (any ECC8x) are preamp tubes and
candidates for swapping. The EL84's, 6L6's, 6V6's, EL34's, 5881's, 6550's and
KT66's to name a few, are power tubes. The 5AR4's, GZ34's, 5Y3's, typically the
tube furthest from the input jack and closest to the power cord, is the
Preamp tubes serve a number of purposes, amplifying the relatively weak
signal from your pickups, shaping tone and changing the gain of the amp. There
are as many different colors and opinions on tone as there are guitar players,
so this search for tone is a personal one. Typically, the more pre-amp tubes,
the more gain stages in the amp. High gain amps with channel switching like a
Boogie will have more preamp tubes than a simple amp like an Epiphone Valve Jr.
which has only one preamp tube. When you get started with preamp tube swapping,
start easy. There is a wealth on information online about preamp tubes, tube
equivalents and tube gain, but when you are getting started, just find another
tube out there with the same number.