The first vacuum tube guitar amp I owned was a Fender Blues Jr. I got it back around 2004 and while it always sounded good, it didn’t compare to vintage and vintage reissue classic Fender amps.
The main problem is that it sounded a bit boxy and thin, but mainly, since I had acquired a couple of good sounding older amps, I wanted an excuse to try my hand at modifying the Blues Jr.
I had read about the BillM mods for years and 3 years ago purchased the parts for some of the most important updates.
I got the amp disassembled, the main circuit board removed and all of the old components unsoldered, then let it rest for over 2 years. I kept track of all the parts and recently decided to finish performing the mods.
The modifications beefed up the power supply with increased and improved filtering capacitors and also upgraded the signal path caps. In addition, I installed a bias adjustment pot, upgraded the input jack from plastic to metal, and changed the reverb and master volume pots to audio taper pots.
The result? It does sound better. The bass is tighter, and the overall sound benefits from both the stiffened power supply as well as the higher quality audio caps. There is still some of the boxy sound, but that’s largely due to the cabinet compromises. It’s an 12″ speaker in a cab that’s just a bit too small.
Overall, I’m glad I made the changes and recommend them to anyone who is considering performing the updates.
Below are a few photos I took towards the end of the operation.