The Fender Blues Jr and Pro Jr, were a couple of low-cost amps that I think were aimed at riding the “All things Vintage” wave, with some modern touches and best of all, a small price tag. The customer I modded this for payed about $25 for this one on Craig’s List. Not bad for a bedroom rocker or small club gigging amp. The cons are that they sound pretty nasally and have the dreaded Kleenex box midrange that immediately strikes them from my list as far as sounds I want to listen to. Also, when overdriven, they completely squash and have no low end, and and and….
Ok,enough! Anyone who has done any surfing of the web for mods to the aforementioned amps will have run across the web site of Bill M, considered by many to be “The Guy” to get your Blues Jr tweaked into useable shape. His website http://billmaudio.com/wp/ is veritable cornucopia of useful mods and upgrades to make your Blues Jr an actual nice sounding amp. Bill not only does the work, but kindly shares his knowledge with detailed descriptions and pics on how to get the most out of your amp. so, I said all that to preface a call I got from a potential client who asked if I could do the “BillM Mods” to his Blues Jr? Up to this point , I knew nothing about Bill M or his mods, but I said sure. run to the computer, look up this BillM character and find out what make his mods so darn special. A week later a new client is standing in my basement with little pride and joy and we start discussing what all he wants done, “All of it”. Ok I can do that! That’s pretty much my pat answer, because If I don’t know how to do it off the top of my head, I will spend many sleepless nights until I find out how to do it. a character flaw perhaps, but I like to think of it as my secret weapon.
There are a lot of so-called “mods” floating around out there, that usually amount to no more than a component change and that’s it, the Bill M Mods are well thought out, and researched thru 1000’s of amps. Best of all, they work. First of all the reverb circuit on these amps is awful, every time the volume changes, the reverb changes, and it’s noisy and hums badly. cover your ears kids…”it sounds like ass”. No maybe you like the sound of ass, I don’t happen to. By rerouting the ‘verb send and return to before the master volume, it makes a world of difference. That tweak is very simple and requires disconnecting one cap and jumpering it to another part of the board nearby and “Poof” the reverb sounds nice and stays consistent no matter where the volume is set at. Next up is the tone stack mod, which changes the bass & mid caps to alleviate the overbearing mid range hump you get with the stock values. While you’re at it, why not change the other coupling caps. Bill mentions this in the kit description, but I couldn’t find any pictorial evidence of it, so I took my reading of it to be true and replaced the preamp coupling caps and the post-PI coupling caps with 716p series Orange Drops. I’m sure one of the reasons they didn’t come stock with these is that they’re about 4x the size of the tiny Xicon chicklet.
It’s kind of a squeeze getting them in there, but can be done. A little hot glue and silicone also help to minimize shock and vibration, as they are now off the board slightly. Actually, in the above picture, you can see just about all the changes done. To the right in the corner, is the 1st preamp coupling cap (.0022uf); in the middle are the tone stack caps (you’ll notice the black one is a Solen, which is a better fit than the OD). Above and underneath the tone stack caps is the reverb change. Word of warning, if you’re doing these mods to your amp, do the reverb first, as the wires and resistors go underneath the tone caps! One other tweak was the “Twin tone Stack” mod, which comprises a jumper between the left/middle legs of the middle pot. This gives you the ability to remove the mids all together in the first part of the pot rotation then bring them in as you turn it up, nice touch. Lastly, doubling the first stage filter cap by adding another 47uf helps the mushy bottom when the amp is turned up, and lowers the AC hash in the B+ supply.
I hate to be derivative, but the amp is really a different beast now. Gone is the boxy annoying midrange, which is probably the biggest complaint people have with this amp. Also gone is the veiled quality of the sound in general. The tone spectrum is much better now, with a lot more bass. It has more of the character of the Blackface amps now, with a more scooped mid and prominent bass. If you’re comtemplating changing the speaker, hold off until you’ve done some of these tweaks, as you just might not want to replace it afterwards. I know a lot of folks go crazy trying to find a speaker that helps the sound of a stock Blues Jr, and never really get there.
Oh, I almost forgot. Probably the most important change was to make the bias adjustable. Stock these amps drive the output tubes at about 90% of max plate dissipation. While that makes it sound like a cranked Marshall, it burns thru tubes, melts the solder joints on the output sockets and makes the amp noisey with no clean headroom at all. The fixed resister network is replaced by a precision trimpot that allows the user to dial back the bias to a more sane 60%-70%, which will give your tubes some breathing room, reduce the noise and clean it up a bit. Nice!
The mods are easy to do, if you have a basic level of competency with a soldering iron. Be aware that you have to pull the board out and deal with removing components without destroying the delicate circuit traces. So, if you’re at all unsure of your abilities, let someone you trust do it.
Peace out,
Matthew M