Amps Blues Junior Modifications

[tom4film]

I finally finished a series of modifications on my Blues Junior and thought the group might be interested in my impressions.  
My Blues Jr was an older model.  I traded for it used at a local guitar store.  The Blues Jr comes in two designs: green circuit boards from 95 – early 2001 and cream colored boards from 2001 on.  The cream boards addressed several issues with the green board so several of the modifications were to update the green board to be more like the cream board.

Power Tubes: New JJ’s for the EL84 power tubes.  I like these a great deal.  My amp had a mismatched pair so this helped a great deal.

Preamp tubes:  Replaced the 1st preamp with a 12AY7.  Has only 50% of the gain the standard  12AX7.  This creates more clean headroom and more gradual distortion.  Ultimately nearly as loud but the distortion does not start until 7 or 8.  

Speaker: Celestion Greenback sounds smokier than the stock unit.  A little less efficient than the stock unit and seems quieter

Input Jack:  This might be my favorite change.  BillM (billmaudio.com $10) sells an all metal, well isolated Switchcraft jack with a coaxial cable.  I used the recommended installation which required drilling the circuit board, cutting a jumper and soldering.  The cable bypasses a noisy section of the green board traces.  This really helped cut noise and hum.  Highly recommended for a green board.  With a cream board, the layout is different so the noise from the traces is not as significant.  It does help the cream board by providing better ground loop isolation.

Power Supply Capacitors and Tone Capacitors ($25 green board kit from BillM):  Installed the power supply capacitors.  This doubles the power reserve which improves the bass noticeably.  I also installed his replacement tone stack capacitors included with the kit.  No real opinion on the tone stack yet.  Need to play with it some more.

Reverb circuit: Parts came with the kit above to make a green board reverb more like the cream board circuit.  This mod was a significant improvement to the reverb.  Reverb is less noisy and sharper plus it follows the Master Volume control now.  My one mistake was installing this circuit.  It is much easier to install before the Tone Capacitors are changed.  Ideally the sequence would be remove the old tone caps, install the reverb mods, and them install the new tone caps.

Output Transformer:  Someone had replaced the original transformer before I acquired my unit.  I sprung for the Mercury Magnetics.  They are overpriced but I have used several of them and they do a wonderful job.  Physically they are twice the size of the OEM unit.

The  TwinStack Mod just soldering a jumper on the Middle control.  No real opinion on this yet. Requires more playing.  

A couple power supply resistors were replaced with higher wattage, tighter tolerance parts.  Fender did not leave much margin for error in component sizing.

Finally, I had a great time drilling, soldering, etc. and like the amp much more.  The hum and noise are practically non-existent.  There is more clean headroom, sharper bass and I like it better at lower volumes.

If anyone is contemplating similar modifications or has questions, please ask

 

[gpower]

Re: Bles Junior Modifications

Excellent review of the mods.

 

[johnc]

Re: Bles Junior Modifications

Thanks Tom, excellent!  Very helpful info.

 

[Chuck]

Re: Bles Junior Modifications

Some of these Mods are sure to help me at a later date. I'll start with tubes and see how it goes! Tom, on your board Mods, could you have done them one at a time in order to see the difference that individual Mod makes?

Right now, the only thing with the amp I'm not happy with is the Reverb, but I've not liked the Reverb on any of my amps, that's why I bought the Hardwire Reverb pedal (Problem Solved!).

 

[560sdl]

Re: Bles Junior Modifications

Tom,

In ballpark terms, what did all the mods run you cost wise?  I am sure mine BJ is a stock older unit.   Not really having any problems with it but I may want to beef it up a bit as a project.  I still have a mod kit to install in my BD-2, so while I am soldering..............

 

[tom4film]

Cost Breakdown:

JJ EL84's matched pair = $29.90 including shipping thetubestore

12AY7 Preamp tube = $15

Input Jack + BillM mod kit = $40 including shipping billmaudio.com  Kit includes Power Caps, Tone Stack Caps, Reverb Mod, and Bias Control.  I did not install the bias control.  I plan to replace the power transformer to change the bias voltage.

Celestion Greenback = I think these are around $100.  I traded for mine

Mercury Magnetics Output Transformer = $90  BillM sells a David Allen-designed 22 watt Heyboer output transformer with a 4/8 ohm switch for $70.  I just like the people at Mercury and try to support them.  They have great customer service and are extremely user friendly.

Mercury Magnetics Power Transformer = $120.  Not installed yet.  

I did the mods in several stages.  I wanted to hear what they did so I would reassemble and play/test before the next change:  Tubes -> Speaker -> Output Transformer -> Input jack -> Power Caps and Tone Stack -> Reverb  (this was an error - do the reverb with the Tone Stack it makes it much easier)

The Reverb Mod does not make it a great reverb.  It improves the older Fender design to be more like the current design although it does change one resistor to add a bit more drive to the reverb.    Overall a huge improvement for the old design but I can not compare it to a newer unit. I also have the Hardwire Reverb.  Normally, I set the Blues Jr reveb low 3 or 4 to get the sound I like.

 

[Chuck]

There are a good number of people on the Forum with Blues Jr's, I'll Sticky this report for awhile so that everyone has a chance to see it before it ends up buried!

Thanks for the help, awesome information! I've copied and pasted your notes in my notebook for future reference.

 

[Bluewater]

Although not modified, here are pics of my Creme Board BJ taken apart. I thought these pictures would be a benefit for future reference. Click on the pictures to zoom in. There is also a link to the schematic below.

 
L>R(Audio Output Transformer, Tube/Jack Decal, Power Transformer)


L>R( Eminence Speaker, Creme board, SN Plate)

A higher resolution picture of the Creme Board is here:
http://www.4shared.com/file/114568373/354ca506/BJ_Creme_Board.html

The Schematics and board Layouts for both the Green Board and Creme Board BJ's is here:
http://www.4shared.com/file/114571162/18bc1685/Blues_Junior_Schematic.html
Be Sure to look at the dates in the revision blocks (top right on each sheet) to determine the board type:
Green Board Released 3-3-95
Creme board Released 21 March 01

Sincerely,
Dave

 

[Chuck]

Great Post Dave!

 

[johnc]

Thanks Dave, you can put your amp back together now.

 

[Stan]

Blues Junior Reverb no working

hi, looking for some help for a buddy who has a Blues Junior about 3yrs old, lives on a boat so amp has been in marine environment for all that time, what has happened is that the Reverb stopped working, if anyone has any ideas of the problem and perhaps a solution it would be much appreciated,

btw this will have to be a fix it ourselves as too far and costly to send to north america for repairs, so any details of the how to and drawings or where to find such would be a great find as well,

cheers

 

[Bluewater]

Fixing the Reverb Tank http://billmaudio.com/wp/?page_id=46
"The reverb tank is definitely a weak spot, but its most common problem is fixable if you have the time and patience." Billm Audio.

Dave

 

[Stan]

excellent link dave i'm sure it will help sort the problem out,

this forum is the bestest

 

[tom4film]

Dave -

Adding the photos was a brilliant idea.  I just posted the photos I took when I first opened my Blues Junior.  The photos are very helpful for the reassembly, especially the transformer connections.  The transformer connections are not identified by color on a green board.

http://www.4shared.com/dir/17156425/eaf91359/BluesJuniorBefore.html

I will post the after photos when I get the next transformer installed.
Tom

 

[Chuck]

I have just ordered the JJ/Tesla tubes. I hope this matters for a step 1 (With an amp that I'm actually happy with!).

Chuck

 

[MikeS]

Jeesh, you guys amaze me. tearing into your amp like that! I'm nervous about doing a set up on my guitar after restringing! Still haven't gotten up the nerve to do it, though I can't really play it like it is. Going from 9's to 10's really lifted the strings off the fretboard. Maybe I'll get up the nerve this weekend. I'm glad I bought the EPI Special that same weekend that I bought the Strat! At least I have something to play.

 

[johnc]

Hey Chuck,  I think the stock amps are great.  But in saying that, commercial pressures dictate a compromise.  If Fender put the best of everything in then it would be a boutique amp at a boutique price.

I look at it as the 80% rule in that to get the amp at 80% of its potental it can be produced at a competative price. To get it to 90% you can double the price for that 10% extra improvement. Triple the price to get it to 95% and so on.
Of course DIY doesn't cost as much, but it's your time.

So all these mods to anything we buy, yes do improve them and it can be a bit of fun and discovery along the way but it's just up to the individual to consider how far do you go and how much do you overcapitalize the item if that matters to you.

For me I do like upgrades that arn't too expensive and the tubes are a good one to do because I would buy a spare set of tubes anyway.  So I would prioritise the mods as to what improvement you get vs the cost.  Trannys and Speakers are getting up there in price unless you pick up a bargain, so they would need to be considered more carefully.
If you don't mind spending the cash and just have a bit of fun experimenting with recommended mods then it can become a bit of an interest on the side. Nothing wrong with that so long as it's not too much of a distraction from our main purpose of playing guitar.

So what I am trying to say?
Depending on your budget spend your money on the best bang for the buck, after all we buy the BJ's because they are economical, and a few mods can make them better for sure.  But how far do you go, how much time do you spend?  If you enjoy doing it great and if it's not your thing then amp is fine as is.
But like I was saying to you with the EQ pedal, it might make more sense to buy a good EQ which will benefit your sound through any amp and can compensate for minor inefficiencies in the amp or guitar.

I have bought mod kits for all my Boss pedals and I believe that they are worth doing.  Allowing about 2 hours labour per pedal and for average of about $25 for components it seems OK.

With my amps I have only upgraded the tubes to a JJ's set in both amps.  The stock tubes are packaged back up and sit in the back of the amp cab for emergency spares.  If a speaker failed I would upgrade it then to something perhaps better.

 

[Chuck]

Thanks John! I agree whole heartedly! My EQ Pedal (Boss GE-7 & my SD-1 are on the way as we speak!) The Tubes are coming too, and I'll BUbble Wrap the old ones and keep them in the back as you suggest!

 

[Stan]

Does anyone know where i might get a retailer to ship a Blues Jr out of the USA to me in the Caribbean, i've contacted all the major retailers and all say NO............................ :'(

 

[stratogeezer]

Have you tried the internet retailers?
Seems to me they should be able to ship anything almost anywhere.
It's not like you are in a war zone.

You can always do some research on how to ship from the US to the Caribbean.
Buy the Blues Jr. and have it shipped to someone you trust in the US and have them forward it to you via DHL or FedEx.