Weekend Mod Project: BillM Blues Jr Mods, Part 1

I worked in guitar shops throughout high school and college, and began tinkering with guitar electronics soon after coworkers taught me to wield a soldering iron. After more than a decade of DIY jobs, I feel comfortable toying with the innards of most control cavities. That said, passive guitar circuits are relatively simple. Amps are another matter entirely; even the simplest designs put a guitar circuit to shame, and most amps can store a lethal electrical charge in their capacitors — even when unplugged. So I’ve generally left amp repair and mods to the experts.

As readers know, it can be hard to suppress the DIY instinct, especially when other pickers are raving about a particular mod. Recently, the itch to tinker with my Fender Blues Jr finally reached critical mass. For several years, I had read rave reviews of the so-called “BillM mods” — circuit modifications from the mind of Jr guru Bill Machrone that most players seem to agree yield a dramatic improvement in the little amp’s tone.

My Blues Jr is about 10 years old, a Christmas present from my parents when I was still in college and wanted a small tube amp for practicing at reasonable volume in the dorms. The 15W, 1×12 amp is one of Fender’s most popular modern designs — a function of price point, tone, and the fact that it pushes quite a bit of air for a “practice” amp (I’ve generally found the amp has more than enough volume for most bar gigs). The Jr has its limitations though, including a tone profile that is somewhat one-dimensional and boxy on the low end, with a brash mid-range and treble that some find an acquired taste. It’s a great sound for blues-rock overdrive (my focus a decade go), but many players find the amp lacking in other contexts. In my case, the limited sound sculpting allowed by the circuit diminished its jazz utility; inspiring clean tones seemed beyond the amp’s capacity.

One can’t wholly blame FMIC for these limitations; the amp represents a compromise between production cost, construction complexity, and the tone preferences of Fender’s target audience. However, Machrone contends that the amp’s flexibility can be enhanced through relatively minor changes to the circuit — particularly through upgrading several important tone capacitors, minor modification of the tone stack a la the classic Fender Twin, and the ability to lower the voltage pushed through the amp’s EL84 power tubes (aka adjusting the tube “bias”). These constitute the “basic” Billm mod package; kits can be purchased for a mere $22-27 direct from Bill’s website (beware of eBay imitators). The actual parts involved are relatively inexpensive; you are really paying for Bill’s knowledge and detailed installation guidance.

You can see where this is all going — I inevitably caved to my baser instincts. I went ahead and purchased the basic kit, plus two additional mods: a presence control permitting additional sculpting of the treble profile, and a more durable input jack to replace the PCB-mounted original. At the time of my purchase, I intended to haul the amp off to a tech for the mods, still fearing lethal voltage and the potential of doing irreparable damage. However, the more I read through Bill’s detailed website, and the more I read through feedback from pleased modders, the more it seemed this task was within my skill set (the DC area is also lacking in conveniently located and reasonably priced amp techs).

Stay tuned for Part 2, in which I weigh in on the mods and reveal whether or not I survived the process sans electrical burns…

Follow link for Part 2.

One thought on “Weekend Mod Project: BillM Blues Jr Mods, Part 1

  1. anyone have the written instructions for the basic mod kit from billm for the bjr. I bought the kit last year and finally getting around to installing the parts.

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