Fender Blues Jr Conversions

[danfrank]

Hi everyone!
I received a message from another forum member here asking about my Blues Jr Conversions... The FBJ makes for a good starting place to build up into a nice combo and because of the Fender's short cuts to keep costs of the FBJ low, there are plenty of broken beyond repair FBJs out there in the wild. For me, what makes them attractive for rebuilding is the cab, chassis and speaker. Sometimes I'll use other parts from within, but the above three parts are a good starting point.
Attached are some pics of one I'm working on now. I'm converting it to a JCM800 master volume style combo, so it will be like the 2203's little brother but combo style.

 

[danfrank]

This one will use EL84s for the power tubes so it should be good for 15 watts output. I did use the output transformer from the original FBJ as I'm still using EL84s in the conversion. The power transformer is an old stock Stancor that makes the right voltages for the EL84s. The original PT had literally melted because there was a short in the original FBJ. The original PTs on these are seriously under-rated, they would be good for a preamp but way too small for a whole amp.

 

[Robert]

Every time the Blues Jr comes up I feel the need to post this. I had one a few years ago with some tweaks in a Deluxe-sized pine cab.

Hand-etched nameplate with my sons name on it.

Really miss that amp! It was fantastic.

 

[jubal81]

Love to find a broken one cheap. Perfect for a Lightning or Carmen Ghia.

 

[Coda]

I have a Blues Jr that was modded by BillM sometime in the early-2000’s. I’ve never played a stock FBJ to compare it to, but I have always been satisfied with it. My amp has the presence control with treble boost, upgraded speaker and transformer (runs at about 18w now) and upgraded tone stacks.

 

[danfrank]

A stock Blues Jr isn't a bad sounding amp, they're just prone to many problems, mainly due to the heat and under-rated parts used.

 

[PapaBear]

I modded one years ago for a buddy I think it was actually a Wampler Mod (indyguitarist days) he said it was like I took a blanket off the amp that had been muffling the sound, I also replaced the reverb unit, which I think was the original issue

 

[dgrainger]

I'm in the midst of slowly converting mine over to the plexi schematic at 18watt.com. having a lot of fun and it sounds really good at my current point in the process.

 

[Harry Klippton]

I love this

 

[thesmokingman]

I worked on so many that it got to the point where unless they were putting them in a properly sized cabinet I wasn't interested because you could pour all your voodoo into one and that undersized original cabinet would just choke the life right out of it.

 

[dgrainger]

I think that's more about the circuit and components. (For instance, just cutting the NFB resistor out made a huge difference ) . The cab is very similar in size to a tweed deluxe.

 

[fig]

Solid wood (I like pine) baby!

 

[sticky1138]

I am a big fan of the Jr., especially the new IV which is a huge improvement over previous models. A lot of the tone concerns fall on the cabinet, so I'm baffled why Fender still hasn't added an external cab output. It seems like an easy fix and most other tube combos have them at this price point.

 

[danfrank]

There is a "cab output"; you reach in and unplug the internal speaker 1/4" and plug in the cable that goes to the external cab. Lol! Yeah, I know... Not the easiest way to plug in...
It's really amazing how much fuller the sound of these amps are when plugged into a proper speaker cab.

 

[fig]

Yep. I have an extra deep solid pine finger-jointed 1x12. It sounds amazing when plugged into the BJIV.

 

[TheSin]

Great idea, thanks for posting!

 

[danfrank]

So here's the end result. I'll test it out tomorrow, I've been working on this all day and I'm tired.
Yes, I know, IC caps!! Oh no! I'll change them out but yes, I'm a total hypocrite for putting them in here! Lol. You gotta do what you gotta do! I need this up and running by Tuesday so a friend can try it out.
Nice thing about EL84s is that they require so little bias voltage... For the bias supply I used the unused 5 volt rectifier winding of the power transformer in a voltage doubler configuration. I should get around 14 volts for bias, should be plenty for a 300 volts B+ supply.
Attached are a couple of pics of the FR4 board I used for components. It's 0.125" thick which should be sturdy enough! Lol. There's an internal HV fuse, I install these on all my builds. It's cheap insurance in case an output tube shorts, which is a case of "not if but when".
Enjoy!