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Fender Blues Junior Mods?

LPJR86

Member
Messages
24
Looking to do some modification on my stock blues junior. Anybody have some good mod recommendations? Thanks.
 

Don.

Member
Messages
17
I've got a blues jr, and have done a few different mods. I recommend Bill's mods if you are comfortable working on a circuit and using a soldering iron.
They are good bang for the buck. I think a replacement speaker would be an option, depending on your goals for your amp.
 

Muzzy

Silver Supporting Member
Messages
3,220
Yeah, Bill's the man when it comes to Blues jr's. He knows more about those amps than anybody.
 

Joe L

Silver Supporting Member
Messages
1,387
Basic Cream Board Mod
Twin Stack Mod
Add Presence control
Clean boost Mod
T020 O/T
Octal Mod
C- Rex Speaker
JJ 6V6s power Tubes
Ruby Reverb Tank
Stand By Switch

Not all of these mods certainly are necessary, but the tone got better with each one.
 

Tiax

Member
Messages
10
CITAT FROM.: DIYampmods.com

Signal flow

All the various revisions are very similar, the main difference being the cap after the first gain stage and the
voltage divider after it. The difference this will make is that the earlier versions will have a little less bottom end
and maybe a little more distortion with the volume low.
While Fender calls the pro junior and the blues junior basically the same circuits, the reality is that they are not.
Nor are they copies of the vintage champs. They ARE, however, very nice sounding circuits on their own…
especially for the price!
Let’s look at the latest version (rev. “F”) and discuss what the signal is doing.
The signal comes in at R1 and C24 is filtering out radio frequencies and stray noise. The signal goes to the first
gain stage, V1b. Gain on this stage is set at C22 and R4 which are going from cathode to ground like most
tube gain stages. R3 controls how much voltage the tube gets, and as always we can make the resistor larger
if we want a dirtier tone or smaller if we want cleaner tone. R10 on the next stage can be changed the same
way.
The signal goes out through C1, and through a hi pass filter of sorts, C2 and R5. Also note that R5 and R6
form a voltage divider, effectively sending signal to ground before the next stage. We can increase R6 a bit for
more distortion but if we go too much it will get muddy. We can also increase C1 for more signal and more
bottom end but there again, We must adjust R6 accordingly or the tone will get muddy.
The “volume” and “tone” controls are a nifty little circuit. The volume control in this location would be called a
“gain” control if there were a master volume on this amp. For this reason, you will notice that the volume
doesn’t get much louder after turning the dial past 4 or so. You just start increasing the gain. It IS possible,
however, that you could install a 100k or 200k pot or so in place of R6 and have what would operate like a gain
control.
The Volume control allows signal to go past but the tone control is also getting signal from the C2/R5/R6
junction. This acts as a hi pass filter with the tone knob turned up and a low pass filter with the tone knob
turned down. So, as you turn up the tone, you increase the highs and lose some bottom end once you are past
about halfway or so. Changing C3 will change what frequencies of highs you have with the tone control up, and
changing C4 will change what frequencies are filtered with the tone control turned down. Note that the tone
control works in conjunction with the volume so the more the volume control is turned up it will ALSO affect the
tone pot as well. With the volume turned up all the way you are not getting the hi pass filter aspect of the tone
control, only the low pass tone. This is normal and is just part of the drawbacks of the tone control design.
After the volume and tone controls influence the signal, the signal goes through R9 before heading into the
next gain stage, V1a. This time there is only a resistor on the cathode so if you want more volume/ gain / and
bottom end, add a cap in parallel with R11.
The signal goes from this stage into C6, which is the phase inverter. A cool mod here if you want to add a
presence control is go connect a 10-22k pot in front of C5. You would just connect it like a variable resistor (as
detailed in the beginning DIY books available at http://www.guitartone.net/ ). In addition, we can change the
“feedback” giving it more volume and more bottom end and clarity by removing R27 totally or by increasing the
resistance.

Effect Rev B circuit board
More bottom end C1,.022uf
More gain, breakup sooner R6, 100k
Less gain, more headroom R6, 22k
More treble and clarity C2, 80pf – 120pf
Overall more gain R3, R10: 220k
Less high mids (“honkiness”) when tone knob is turned up C3, .0047uf or .0022uf
Less highs when tone knob is turned down C4, .0047uf - .01uf
Feedback circuit, changing feedback will alter bass response
and gain. Remove for more “open sound”
R27, remove or for a tighter smoother response
change to 82k.
Better overall tonality, response, clarity, and lower noise floor
by changing inferior components to higher quality
components. Note that not every part needs changed as
some have no direct effect on tonality, response, or noise.
Metal Film Resistors, 1/2 watt:
R1: 10k
R5: 470k
R9: 100 ohm
R27: 100k or as noted on modification above
R21: 220k
R22: 220k
R26: 270 ohm
Mallory or Orange Drop caps:
C1: .01uf
C3: .01uf or as noted on modification above
C6: .01uf
C5: .1uf
C7: .1uf
C8: .022uf
C9: .022uf
Silver Mica Caps:
C2 22pf or as noted in modification above
C11: 2200pf (.0022uf)
More gain, breakup sooner R4, R11, Add a 22uf cap in parallel with R4 and a
47uf cap in parallel with R11

Effect Rev C
More bottom end C1,.022uf
More gain, breakup sooner R6, 100k
Less gain, more headroom R6, 22k
More treble and clarity C2, 80pf – 120pf
Overall more gain R3, R10: 220k
Less high mids (“honkiness”) when tone knob is turned
up
C3, .0047uf or .0022uf
Less highs when tone knob is turned down C4, .0047uf - .01uf
Feedback circuit, changing feedback will alter bass
response and gain. Remove for more “open sound”
R27, remove or for a tighter smoother response change to
82k.
Better overall tonality, response, clarity, and lower noise
floor by changing inferior components to higher quality
components. Note that not every part needs changed
as some have no direct effect on tonality, response, or
noise.
Metal Film Resistors, 1/2 watt:
R1: 10k
R5: 470k
R9: 100 ohm
R27: 100k or as noted on modification above
R21: 220k
R22: 220k
R26: 270 ohm
Mallory or Orange Drop caps:
C1: .01uf
C3: .01uf or as noted on modification above
C6: .01uf
C5: .1uf
C7: .1uf
C8: .022uf
C9: .022uf
Silver Mica Caps:
C2 22pf or as noted in modification above
C11: 2200pf (.0022uf)
More gain, breakup sooner R4, R11, Add a 22uf cap in parallel with R4 and a 47uf cap
in parallel with R11

Effect Rev D
More bottom end C1:.033uf or .01uf for less bottom end
More gain, breakup sooner R6, 56k – 68k
Less gain, more headroom R6, 10k - 22k
More treble and clarity C2, 80pf – 120pf
Overall more gain R3, R10: 220k
Less high mids (“honkiness”) when tone knob is turned
up
C3, .0047uf or .0022uf
Less highs when tone knob is turned down C4, .0047uf - .01uf
Feedback circuit, changing feedback will alter bass
response and gain. Remove for more “open sound”
R27, remove or for a tighter smoother response change to
82k.
Better overall tonality, response, clarity, and lower noise
floor by changing inferior components to higher quality
components. Note that not every part needs changed
as some have no direct effect on tonality, response, or
noise.
Metal Film Resistors, 1/2 watt:
R1: 10k
R5: 470k
R9: 100 ohm
R27: 100k or as noted on modification above
R21: 220k
R22: 220k
R26: 270 ohm
Mallory or Orange Drop caps:
C1: .022uf
C3: .01uf or as noted on modification above
C6: .01uf
C5: .1uf
C7: .1uf
C8: .022uf
C9: .022uf
Silver Mica Caps:
C2 22pf or as noted in modification above
C11: 2200pf (.0022uf)
More gain, breakup sooner, more bottom end R11, Add a 47uf cap in parallel with stock resistor (1.5k)

Effect Rev E
More bottom end C1:.033uf or .01uf for less bottom end
More gain, breakup sooner R6, 56k – 68k
Less gain, more headroom R6, 10k - 22k
More treble and clarity C2, 80pf – 120pf
Overall more gain R3, R10: 220k
Less high mids (“honkiness”) when tone knob is turned
up
C3, .0047uf or .0022uf
Less highs when tone knob is turned down C4, .0047uf - .01uf
Feedback circuit, changing feedback will alter bass
response and gain. Remove for more “open sound”
R27, remove or for a tighter smoother response change to
82k.
Better overall tonality, response, clarity, and lower noise
floor by changing inferior components to higher quality
components. Note that not every part needs changed
as some have no direct effect on tonality, response, or
noise.
Metal Film Resistors, 1/2 watt:
R1: 10k
R5: 470k
R9: 100 ohm
R27: 100k or as noted on modification above
R21: 220k
R22: 220k
R26: 270 ohm
Mallory or Orange Drop caps:
C1: .022uf
C3: .01uf or as noted on modification above
C6: .01uf
C5: .1uf
C7: .1uf
C8: .022uf
C9: .022uf
Silver Mica Caps:
C2 22pf or as noted in modification above
C11: 2200pf (.0022uf)
More gain, breakup sooner, more bottom end R11, Add a 47uf cap in parallel with stock resistor (1.5k)

Effect Rev F
More bottom end C1:.033uf or .01uf for less bottom end
More gain, breakup sooner R6, 56k – 68k
Less gain, more headroom R6, 10k - 22k
More treble and clarity C2, 80pf – 120pf
Overall more gain R3, R10: 220k
Less high mids (“honkiness”) when tone knob is turned
up
C3, .0047uf or .0022uf
Less highs when tone knob is turned down C4, .0047uf - .01uf
Feedback circuit, changing feedback will alter bass
response and gain. Remove for more “open sound”
R27, remove or for a tighter smoother response change to
82k.
Better overall tonality, response, clarity, and lower noise
floor by changing inferior components to higher quality
components. Note that not every part needs changed
as some have no direct effect on tonality, response, or
noise.
Metal Film Resistors, 1/2 watt:
R1: 10k
R5: 470k
R9: 100 ohm
R27: 100k or as noted on modification above
R21: 220k
R22: 220k
R26: 270 ohm
Mallory or Orange Drop caps:
C1: .022uf
C3: .01uf or as noted on modification above
C6: .01uf
C5: .1uf
C7: .1uf
C8: .022uf
C9: .022uf
Silver Mica Caps:
C2 22pf or as noted in modification above
C11: 2200pf (.0022uf)
More gain, breakup sooner, more bottom end R11, Add a 47uf cap in parallel with stock resistor (1.5k)
Clearer tone C24, 22pf
Notes:
C1, R6, R8, and C2 all work together so when you change C1, for example, you’ll want to change R6
as well or the tone can start to become mushy. If you have a B or C version of the Pro Jr. and you
change C1 to a .022, you’ll want to lower R6 to a 22k or so… or a smaller resistor than that for less
gain/more headroom and a larger resistor for more gain and less headroom.
 
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Tiax

Member
Messages
10
CITAT FROM BILLM.: The Right Speaker for your Blues Junior

Aftermarket speakers, like tubes, are not really a mod. But they do change the way your Blues Junior moves air and the tones that get emphasized. They may partially mask an amp’s flaws, but the right approach is to make the amp sound great first, then use the speaker to give it that final push in the tone direction you want to go. It should be your last mod, not your first. People who say that a new speaker has cured the Blues Junior’s inherent boxy tone simply haven’t heard a Blues Junior with proper tone stack and power supply mods.
See the bottom of the page for easy instructions on how to change the speaker.
My customers and I have collectively tried many different speakers, but I’ll limit my comments to speakers that I’ve spent some time with and have a feel for the tone.
Fender Special Design (stock speaker)
This is the stock speaker in all black and blonde Tolex Blues Juniors and old green board tweeds. The speaker is made by Eminence and it’s roughly equivalent to the Legend 125/1258. This speaker has been used in hundreds of thousands of Fender amps, including the Deluxe Reverb, Hot Rod Deluxe, Twin Reverb, Blues Deluxe, and many others. It’s a decent, all-around speaker. It doesn’t have the deepest bass, and the highs can sound kind of fizzy, but it’s well balanced. Many people decide to leave it alone after they do the mods. The “farty” tone in the bass of a stock Blues Junior is mostly due to poor design decisions in the amp, not flaws in the speaker. One surprising new observation about the stock speaker: The more power you give it, the better it sounds. My 5881-powered 25-w Blues Junior has the stock speaker in it, and it sounds awesome. The Billm basic mods will go a long way to helping this speaker deliver.
Jensen C12N (stock in tweed limited edition and “NOS” models)
This reissue Jensen is built in Italy by Recoton. They’ve made an effort to capture some of the old “American sound” magic of the Jensens that were so popular in the 1960s, but they fall short in some significant areas. The C12N starts out well in the bass and transitions well to a smooth midrange, but this speaker can be downright shrill on the high end, especially with a Tele or Strat bridge pickup. On the plus side, the C12N cuts well in a band situtation and is less likely to be buried. It sounds better after a lengthy break-in period, but it’s definitely not my favorite speaker.
Eminence Texas HeatThe Texas Heat is one of the most popular of Eminence’s line of Patriot speakers, and for good reason. It has great tonal breadth, strong bass, prominent, slightly smoky mids, and a smooth top end. When The ToneQuest Report tested a bunch of the Patriots a couple of years ago, they reported that the Texas Heat improved every amp they tried it in–and they tried a lot. It’s more efficient than most other aftermarket speakers, so you get your 15 watts’ worth. The only criticism I have of the Texas Heat is that when playing clean, the highs can sound a bit disconnected from the rest of the tone, almost as if my high E string was connected to another, smaller speaker. It sounds better if you roll off the bass and boost the mids a bit to fill it in. And when you crank it, distortion tones are sweet, not spiky and harsh.
Eminence Cannabis RexThe Cannabis Rex gets its name from its hemp cone. Hemp fibers strengthen the cone and impart a different flavor than typical paper cones. The cones are made for Eminence by Tone Tubby, the leader in hemp-cone speakers. This is the warm/clean jazz speaker! It’s a great clean speaker, but its cleans have that hemp cone personality–soft-edged, but not mushy. It handles overdrive and distortion very well when you push it. It’s very efficient, one of the loudest speakers you can put in an amp, and it pushes out pretty, round bass notes really well. The top end is very sweet, even forgiving. This speaker couldn’t make a harsh note if it tried and is beautifully balanced bottom to top. Super for creamy lead work.
Eminence Red White and BluesIf your idea of electric guitar is crisp, bright, staccato bursts, clear, sizzling chords, with lots of top-end sparkle and tight, tight bass, this is your speaker. One player’s “tight bass” is another’s “no bass,” however. So if you like booming lows that flap your pants legs, that you can feel in the soles of your feet, look elsewhere. This is a great lead guitar speaker for many kinds of rock, searing bright country, or to clean the mud off your humbucker tone.
Eminence Swamp ThangThere’s nothing swampy about the Swamp Thang–this is the loudest, cleanest speaker in Eminence’s lineup, but its response is tilted towards the bass side. Eminence calls the treble response moderate, but I find its highs more prominent than the Texas Heat’s. It produces big, round lows, even in the BJr’s small cabinet. The magnet is huge and it will add noticeable weight to your BJr. It might hit an aftermarket, larger output transformer like the Heyboer I use. You can probably spin the baffle 180 degrees to place it at the lower right instead of upper left (from the back) for clearance. I use the Swamp Thang on my test bench because it’s so clean (I want to hear the amp, not the speaker) and the moderate highs keep the ice pick tones out of my ears. The Swamp Thang is not a truly neutral speaker; it adds a warm, woodwind-like undertone.
Eminence GB12/GB128This speaker from the Legend line is Eminence’s take on the famous Celestion Greenback. It’s an improved, affordable Greenback, with great, deep, lows, that classic British smoky tone, bass that manages to be fat and round-toned without being overpowering, strong mids, and nicely restrained highs. It may be one of the best speakers you can buy for blues tone.
Eminence WizardI don’t see many British-voiced Eminence speakers in Blues Juniors, but this one is pretty interesting. The bass is firm, with an aggressive edge to it, not round like the Cannabis Rex, GB128, or even the Jensen C12K. The highs are bright and crisp, also with an aggressive edge to them, like the Red White and Blues, but with more bass. And in true British fashion, the midrange is colored, too. Not smoky, like a Greenback, but an interesting, textured tone, rich with harmonics. This is a very efficient, loud speaker and if your Blues Junior is getting buried, this might just be the thing to unearth it. If you like mellow, stay away. If you like to peel their eyelids back with your bridge pickup or put a serious edge on your neck or ‘bucker tone, this one’s for you.
Celestion GreenbackThe Greenback (G12M) has always been a good choice for the Blues Junior. It’s a bit quieter than some of the newer designs, but the classic, warm British tone is there in spades. This is the speaker that defined “smoky,” that coloration of midrange tones sought after by blues and blues rock soloists. A classic.
Celestion Vintage 30The V30 was one of the tone pillars of the classic rock era: huge, powerful mids and early breakup. Four of these in a half stack and you were on your way to rock god status. But they were often tempered in half stacks by a pair of Greenbacks to fill out the bottom end. The V30 has less bass and less treble than the stock Special Design speaker. Fender chose the V30 for the Texas Red special edition of the Blues Junior and you can hear the difference right away. It’s a standout for lead guitar and for rhythm guitar that stays out of the way of the bass player. If you like thumpy bass or need clean headroom, look elsewhere. Some players say they get more clean headroom with the V30, but I think that’s because the mids are prominent and that’s the most sensitive area of our hearing, so it sounds louder.
Jensen C12KThe C12K is Fender’s current choice for the Deluxe Reverb reissue. It sounds somewhat like the Texas Heat, but much more restrained in the highs, maybe even a little dull-sounding, a little more color in the mids, maybe a little dirtier in the bass. But there’s an impressive amount of bass on tap; with a bit of roundness, like the Cannabis Rex. It’s like a rude version of the Swamp Thang, but the ST is a much better speaker overall. This is a loud, efficient speaker. Like the Swamp Thang or Wizard, you’ll feel the increase in weight because of the huge magnet. Compared to many other speakers, the C12K sounds kind of lifeless. It properly tames the highs of the Deluxe Reverb, but doesn’t bring much to the party.
Weber CaliforniaThe California is Weber’s clean-and-loud speaker, patterned after the great JBL D120. Like the Swamp Thang, it does what the amp tells it to do, but it’s more balanced in tone and brighter. It’s available with an aluminum dust cap, like the original JBLs, but don’t go there! It’ll be way too bright and beamy.
Weber 12F150The 12F150 is Weber’s idea of what a vintage, US-made C12N would sound like if it were offered today. It gets that brash voice-of-rock ‘n’ roll American tone right, and it’s a popular choice among rock and blues players. Bass is solid, mids are somewhat scooped, highs are bright and clear. One potential point of confusion: the many choices of cone and doping options can greatly change the tone. So two players comparing their 12F150s may almost be discussing apples and oranges. A call or email to Weber’s tech staff will get you the right ingredients for your tone, though.
Weber 12A125I was prepared to dislike the 12A125 based on my experience with other light-coned alnico speakers: no bass, early, unharmonic breakup, etc. I tried it in an unmodded Blues Junior and was unimpressed. But after the mods, the 12A125 really surprised me. If you’re looking for a fast, responsive, bright speaker that just oozes Fender “spank,” this is your speaker. It’s bright, like the Eminence Red White and Blues, but it has a nice, crisp bass, like a tenor who can hit clean, clear low notes, not a deep-voiced baritone. This is an inspiring speaker for bright, clean playing–I heard things from my Tele bridge pickup that I don’t think I’ve heard with any other speaker. The highs get great support from the mids, but the voice is pure American, not a hint of British smoke or thickness. Yes, you can go too far with the bright stuff and make it painful, but that’s what tone controls are for. I had a harder time finding a good overdrive tone with this speaker because it doesn’t like complexity. I had my best results starting with the tone controls off and either the bass or the mids up full. then dial in just enough of the others so it doesn’t sound thin or muffled. Get one of these, plus the basic mods, and kick some Deluxe Reverb ass! This speaker is everything the Jensen P12R wished it was.
Jensen P12RFender chose this speaker for the Relic Blues Junior version. The Relic looks like it was made in the 1950s and lived a very hard life, complete with rust, stains, cat-clawed grille cloth, and tattered tweed. The P12R sounds like it’s from the 1950s too… kind of like an old table radio. This speaker makes the Blues Junior sound like a kazoo on steroids: squawky, nasal, thin, and weak. If you like that old-timey sound, you’ve found it. For the rest of us, yuk.

Try this link for sounds of Jensens and other speakers (watford valves
http://www.watfordvalves.com/soundfactory.asp

Speakers that Don’t Fit:

Eminence Red Fang
Tone Tubby Alnico
Celestion Alnico Blue (sometimes juuuust barely fits!)
Weber Blue Dog (seen ‘em fit, seen ‘em hit the chassis)
How to Change the Speaker

1. Leave the back on the chassis.
2. Remove the screw that holds the reverb wires to the side of the cab.
3. Unplug the reverb wires. Note that the red plug is towards the middle of the amp.
4. Unplug the speaker.
5. Lay the amp on its back.
6. Remove the two side screws and remove the two top screws.
7. Reach under and hold the back panel down as you lift the cabinet off the chassis. THIS DOES NOT EXPOSE ANY ELECTRONICS OR HIGH VOLTAGES.
8. Remove the old speaker.
9. Replace with the new the speaker. When tightening, just use enough force on the screws to lightly compress the gasket. If you make it crusher-tight, you’ll distort the frame and maybe ruin the speaker.
10. move the plug to the new speaker. The red dot goes on the + terminal. Reassemble in reverse order.
 
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Tiax

Member
Messages
10
Is there anyone in here who has got a photo of haw to connect the standby switch on the BJ ?
 

Joe L

Silver Supporting Member
Messages
1,387
Billm supplies excellent instructions on how to connect the on/off/standby switch he sells. I know nothing about electronics and was able to do it in 15 minutes and that's taking my time.
 

Jon Silberman

10Q Jerry & Dickey
Silver Supporting Member
Messages
43,101
In the days of my youth, I was told what it takes to salvage a BJ. Now that I'm a man I know to walk away from amps that require all of that effort and still remain essentially what they were at the outset.

Just me. YMMV. But before you take on a set of projects and potentially significant aftermarket costs on a $500 amp, it is worth asking yourself whether you might be better off buying a better amp from the outset.
 

Tiax

Member
Messages
10
Billm supplies excellent instructions on how to connect the on/off/standby switch he sells. I know nothing about electronics and was able to do it in 15 minutes and that's taking my time.
I send you a PM

PS.: Thanks for the info :)
 
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Tiax

Member
Messages
10
Well now I got a 6 legged 2 pole Standby switch, (but without the jumper) and the installation info... Dose anyone knows where from and to the red jumper goes on the switch ?
 
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psb962

Member
Messages
63
...and I believe Billm is no longer with us. RIP, master of the modded Blues Jr, you are missed.
 




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