Blues Jr

[Stu2]

1rst post but been lurking for a while. Have a Blues Jr  2006ish maybe with a cream board. Had a tech mod it around then but can’t remember what I had done. Probably the BillM bias and twin mod but looking at the guts it doesn’t seem to track with those descriptions. Here are some pics of what I’ve noticed. Looks like the caps at c6 and c7 were replaced and two orange drops were wired in series in between pins 7 on the el-84’s. Hopefully the pics will help illustrate. Any idea what these changes did?

[Stu2]

3 more pics

[sluckey]

No idea why C6 and C7 were changed. According to the only schematic I have, the original caps were also .022. Maybe the originals failed, but I think that's unlikely.

The two orange caps act as a filter to help remove some highs and that may help with some harshness. Kinda smooths out the sound a bit. I don't have a BJ but I do have several other EL84 amps. I've never heard a need for those caps.

[tdvt]

Bill M had you do the "Twin Mod" to the tonestack, with a jumper on the back of the board, so there wouldn't be any visuals as to whether or not that was done.

The best clue that mod was implemented is no sound if all tone pots are at zero.

I never did the adjustable bias mod but don't see a trim pot in your pics, so maybe not that one...?

[mozz]

There's a bunch of various versions of the board, funny that the latest one has about all the mods you could find using google. Here is the mods i do and the guy keeps bringing me more amps to mod.


FENDER BLUES JUNIOR
2003 MEXICO
B-190434 PR295
CRÈME BOARD
C5  CHANGE FROM 250PF TO 270PF
C1  CHANGE FROM 47UF TO 10UF
C2  CHANGE FROM .0022UF TO .022UF
C8  CHANGE FROM .0022UF TO .022UF
R30  PARALLEL 100PF ACROSS IT
C4  PUSH SWITCH 10UF .56UF
C6  CHANGE .022UF TO .1UF
C7  CHANGE .022UF TO .015UF
C9  REMOVE 1500PF
C10  JUMPER ACROSS .033UF
C25 ADD 47UF
D11  REMOVE
D12  REMOVE
R54 100 OHMS
R55  100 OHMS

I've had my mods (stolen from the internets and changed a little) dissected by another tech near Philly and he couldn't figure out side by side why mine sounded better.
With the C6,C7, you take out, i use them for C2,C8. It will then stay stock looking, at least for those 2 parts. I also add a variable NFB, 100k i think.

Also, best thing you can do these amps is rip out the pcb for the output tubes and replace with a higher quality board, don't know if something close is sold here on EL34 world.

[mresistor]

yes Hoffman sells BJr tube boards in his store  on this page 
Tube Amp Circuit Board Building parts

[mozz]

That's not the same board. You need to gut the amp/use the other Hoffman board also. If you just want to replace the tube board you need all the traces and use the stock pcb with the factory components. There are sellers on reverb who sell the replacement tube board, it's only $22. I posted a picture of it.

[Stu2]

Thanks everyone. Thought I read the twin mod was a jumper on the mid pot.

[AlNewman]

The twin mod is a jumper on the mid pot, but it's usually on the back side of the board. 

It is probably the best mod on any of the newer fenders.

As mentioned earlier, if you can cut volume to nothing with your tone knobs, it's probably installed.

[Stu2]

Thanks. The electrolytic filter caps need to be replaced so this is why Im looking at all of the Mods people have done. I haven’t done any soldering on this board so I’m a little weary since the pads and traces can be so easily damaged to over heating. Premier Guitar had an article talking about  modding  the BJR. The author wrote that clipping the leads to the filter caps and soldering in new ones top side is doable. Seems that’s a safer course. What’s everyone’s opinion on that?  I built an Allen Old Flame kit  and a pedal kit so I have some experience.

[AlNewman]

I would watch a lot of videos, and learn the tools and techniques needed to work on circuit boards.  You're probably just as likely to screw something up working from the top side as doing it properly from the back.  Just my opinion.

[acheld]

Very tough to work on BJ boards while in the amp, at least for a non-pro.

Honestly, the BJ sounds good stock.   I've done all the BillM mods over the years -- it's what got me into the amp building black hole -- and they do make a difference, but whether it is worthwhile or not is in the ear of the beholder.   Of course the internet fanboys are all in favor of the various things people can do to the amp.

The one mod that is worth doing in all BJ's prior to the BJ4 is bringing the bias of the EL84's under control.  That is accomplished by changing R52 as needed, and/or adding the trimpot to make an adjustable bias.   Of course, this is not needed in BJ4's.

I happen to like Doug's take on the BJ.   Very sweet sounding amp, not quite as chimey as the original (good for my ears), but very smooth.