A couple of years back, I did a couple of the "BillM" mods to my Fender Blues Junior amp, as described HERE. I've been pretty happy with the sound of the amp, especially since changing to an Eminence Cannabis Rex speaker a couple of months back. That smoothed out some treble harshness that I was hearing with brighter guitars. But you guys know me--what's good can always be made even better!

I'd been looking at Bill "BillM" Machrone's new Blues Junior website a few months back and I saw he'd added a bunch of new Blues Jr. mods--some to further improve tone, some to improve the usability of the controls, and some to add features that this fairly low-priced tube amp lacks. Not only that, but he now sells kits for most of these mods at very reasonable prices, with all the parts you need and detailed instructions for the installation. So today, I bit the bullet and ordered a whole bunch of them. Here's the list of the nine (!) mod kits I ordered:

  • Audio taper volume pot
  • Audio taper reverb control
  • All-metal Switchcraft input jack
  • Aux. speaker jack
  • Line out jack
  • Standby switch
  • Presence control
  • 22W Heyboer output transformer with 4/8 ohm switching
  • Octal tube conversion

Many of these are very fast and easy, though a couple are definitely more involved, particularly the octal tube conversion. I'll probably try to work in the mods piecemeal between customer pedal builds, so they may take a while to complete. I haven't done any amp work in quite a while, so this will be a good warm-up for that Trinity Amps 18W kit that I STILL haven't started building! (hangs head in shame)

Additionally, I'll be doing a 10th mod that doesn't require a kit--wiring in the unused half of the V2 preamp tube as a cathode follower between the preamp and the tone stack (see link for the benefits this offers). I'll also be changing the existing 12AX7 tube at V2 to a 12DW7, since the purpose of the cathode follower is to provide current gain, not voltage amplification. The 12DW7 is a "hybrid" tube--a 12AX7 type triode on one side and a 12AU7 triode on the other. Since the AX7 is a voltage gain triode and the AU7 is an excellent current driver, it's ideal for this application. And I just happen to have one on hand!

While all the mods have their individual benefits, I'm really looking forward to hearing what comes from the combination of the Heyboer OT and the octal tube conversion. The amp is said to take on much more of a Fender "Blackface" character with these mods--taut, round lows and a brighter, glassier top end. I've also ordered three sets of octal output tubes to try in the amp: matched pairs of JJ 6V6-S's, Tung-Sol 6V6-GT's and Tung-Sol 5881 Reissues. Machrone has tested 5881's in this modification and reports that the amp will drive them very nicely, and they'll break up earlier than the 6V6's. Plus, the output of the amp jumps up to about 25W from the stock 15W! Should be fun to try 'em all and see which set sounds the best.

The only down side to this is I'm going to end up with about the world's most expensive Blues Junior when I get done. If I ever decide to sell it, I'm quite sure I won't be able to get back out of it what I will have invested. But that's not the point--this is all about tone and flexibility, not economics! Plus I'm tentatively planning to have it buried with me....