A Very Special Blues Junior — Updated!

p5150233-1This is the 1000th Billm-modded Blues Junior.

Or as close as I can figure, given the number of components I’ve ordered over the years, shipping records, etc.

I decided to pull out all the stops on this one. I started with a basic black Blues Junior, the perfect platform for a stealth amp that can blow away some much more expensive hardware.

It’s got

  • Basic mods — tone stack, power supply stiffening, adjustable bias
  • Presence control
  • TwinStack
  • Heyboer output transformer with 4/8 ohm switching
  • Audio-taper reverb control
  • Clean Boost
  • Clean Boost/Fat footswitch control
  • Aux speaker jack
  • Line out jack
  • Cathode follower tone stack driver
  • Standby switch
  • Higher preamp voltages for more headroom
  • and octal power tube sockets for 6V6s — or 5881s!

Here’s a shot of the innards. You can see where I removed the ribbon cables and wired in a pair of ceramic sockets. I used Amphenol military-grade ceramic sockets, which are probably indestructible, but were kind of a pain to install.  As you can see, I’ve got Tung-Sol reissue 5881s installed for testing… and they are awesome!

Update: I’ve upgraded #1000 with the new TP24 power transformer and TO26 output transformer. It now puts out 30 watts of clean power, sounds like a Deluxe Reverb running 6L6s or the cleanest Blues Deluxe you’ve ever heard, with effortless, Fender-y loudness. All the Blues Junior breakup tones are there too, but smoother, less grind-y. It’s a surprisingly big sound from such a small package; I’m loving it!


The EL84 and the 6V6 were designed to be electrically equivalent to one another, but they go about it different ways. The 6V6 is actually a 14 watt tube, while the EL84 is rated at 12 watts. The 6V6 has more plate area, and like its brother 6L6, is actually a tetrode (four elements) with a special plate inside that focuses the electrons into a beam for maximum efficiency. The EL84 is a pentode, and it makes up for its smaller size by running hotter and using a suppressor grid instead of beam-forming plates. But output tube performance is all about plate area and current. Because of the socket and bias differences, it’s not easy to directly compare an EL84-based amp to a 6V6 equivalent, but I can easily compare this one to other Blues Juniors.

The 5881s have even more plate area, which really helps bass response as well as maximum power. The 5881 is also known as the 6L6GB, the version that preceded the current version, the 6L6GC. The 5881 is nominally a 23 watt tube and the 6L6GC is a 30 watt tube.

The 6V6 consumes less filament current than the EL84; the 5881 consumes more. The question is, will the 5881 overtax the Blues Junior’s power supply? And is the Blues Junior’s 330V plate voltage enough to extract power and tone from the 5881, or will it run out of steam? After all, 5881s are rated for 360V operation and it’s customary in guitar amps to run them at around 400V. Power (watts) is volts times amps, so if you increase the voltage, the current goes down. And you tend to get cooler-running power and output transformers with the high voltage/low current formula.  So I monitored thermal rise closely when I installed the 5881s. I’m happy to report that even after hard running, the power transformer was just comfortably warm and the Heyboer OT hadn’t shown any signs of heating. I’ve got more about octal tubes, output power and power consumption here.

Power transformers are limited in the amount of volt-amps they can deliver. When they run out of steam, you get voltage sag. Going full out into a dummy load with 6V6s, there is no sag. With 5881s, the sag was just a few volts. I was frankly surprised that the BJr power supply performed that well. I’ve seen more sag in Princeton Reverbs, and the power transformers in many blackface and silverface Fenders get uncomfortably warm.

OK, so it’s not going to blow up. How does it sound? In a word, heavenly.

Here are some sound files, recorded while a local blues phenom whom I know only as “Matt” sampled the amp. He brought his own Tele, heavily customized to his preferences. These recordings started loud, went louder, with serious ear ringing after an hour or so.

1. Playing first through a modded Billm Blues Junior with EL84s and stock OT, then #1000.

billm bjr then 1000

2. Playing with heavily scooped tone controls, then turning on the Clean Boost.

1000 scooped then clean boost

3. Some dirty, bassy blues, tone rolled back on Matt’s Telecaster.

1000 dirty bassy blues

4. Some riffs on “Ghostriders,” really loud.

1000 loud ghostriders noodling

With 6V6s, the output power is about the same, maybe a watt or two higher at full bore. But the larger plate area makes the bass performance noticeably better than even an “improved” Blues Junior with power supply stiffening, tone stack, and Heyboer output transformer. With no other changes, plugging in the 5881s make the amp 2-3dB louder and gives you the kind of bass thump you’d expect from a much larger amp.  Flat out, it puts out an honest 25 watts clean (5 percent THD). Despite the big bottles, it’s still not going to go toe to toe with a Hot Rod Deluxe, but it can edge out a Princeton and hang with a Deluxe Reverb effortlessly.

The thing that surprised me most about the tone is the touch sensitivity. I expected more clean headroom and I got it. Yes, the amp still gets crunchy between 5 and 7 on the volume control, as a BJr should, but it’s louder than a stock amp at that point. And the power tube crunch comes on in a whole different way, more gradually, right in line with the energy you’re putting into the strings. The Clean Boost helps deliver the extra kick to the output tubes to make this even more evident, but even with the Clean Boost off it feels like a $1500-class amp. I did all the bench testing with an Eminence Swamp Thang, but I was pleasantly surprised when I put the amp back together with the stock Fender Special Design speaker: solid bass, sweet highs, nice transitional midrange, and smooth progress from clean to dirt.

The cathode follower mod is supposed to increase touch sensitivity by taking the load off the previous preamp stage, so that it performs the same regardless of tone stack settings. That appears to be the case, but it’s not an easy thing to verify other than by playing the amp and saying “Wow!”

Beyond dirt and breakup, the highs are higher and sweeter, the lows are more powerful, and there isn’t a hint of boxy.

I also decided to leave the stock Accutronics reverb tank in place. I tested it with the Ruby tank and I could go either way, but the bright, percussive stock reverb just felt more in keeping with the amp’s personality and the audio-taper control lets me bring it in much more gradually than the stock control.


Here are some of the other mods–you can see the Heyboer output transformer, impedance switch, the additional jacks, and the Fat/Clean Boost jack. I’ve converted it to a stereo jack, so you can use a 2-button footswitch to control Fat and Clean Boost independently.


Here’s how it looks with a couple of EH 6V6s–bound to surprise the casual Blues Junior owner who peeks back there!

I’ll probably play some more with screen resistor values because they affect the feel of the output stage, but I’ve gotta say that it sounds pretty darn good.

Now I just have to figure out what do do with it. I need another Blues Junior like John Mayer needs girlfriends. It doesn’t make sense to keep it with my demo amps, because I suspect that most people aren’t going to want to go this far.

What a good problem to have.


  1. S. Riley says:


    I love your site, and I am impressed with the amount of work you have done in mod’ing the BJ. I just purchased a ‘cream-circuit’ one and am considering various mods to sweeten and “unbox” my Junior. I’ll be ordering some of your kits soon.

    In the meantime, I’ve got a couple questions regarding the TS 5881 mod. I assume that the Heyboer output transformer is a required mod to better support the 5881s, correct? Do you recommend the ceramic sockets over phenolic, and does it matter whether I use top mount versus inside mount (e.g. http://www.mojotone.com/item.asp?pid=617779&pg=569613&id=4050004)? Finally, in consideration of a mod like this, do I need to budget for NOS tubes or will the $50 TS5881 tubes from Mojo sound fine? Finally, would you be willing to provide wiring instructions for this if I pursue this in the future? Thanks

    • bill says:

      The cost difference between ceramic and phenolic is minimal–why bother with phenolic? It doesn’t matter whether the sockets are top or inside mount.

      It definitely needs the heavy-duty OT, and the Tung-Sol 5881s are terrific. No need for NOS. I’m still working on heat issues for this mod, and may have a better power transformer to offer in the not-too-distant future.

  2. vince says:

    Can this mod be done to the Pro Jr. & how difficult as I’m a novice. Thanks

    • bill says:

      It could be done, but it’s definitely not for a novice because it would also require revisions to the bias circuit and a new output transformer at the very least.

  3. Neil says:

    I’d like to do this on my Pro Jr., I’m planing on turning it into a 212 combo & already have a Blues Jr.(stock) just wondering can I use my Hammond 272fx Transformer for this? I know it will supply the voltage for El34’s but I prefer the larger bottle tubes. also I have 4 of NOS Sylvania 5881’s around.

    • bill says:

      The Hammond PT provides way too much voltage for the PJ’s full wave bridge. It’s intended to be used with a pair of diodes in a center-tapped configuration. The PJ probably only supplies 140-150V to generate 330V. So you’d have to rework the rectifier setup.

      I’m working with David Allen on designing an aftermarket PT for the Blues Junior that would probably work for the Pro Junior as well. It would supply more current for the filaments in octal tubes, correct voltage for the bridge rectifier, and more available bias voltage for high-power tubes.

  4. Neil says:

    ok, thanks I see now.

  5. Reid says:

    Hi Bill,

    Is the tube socket going to become a kit? Are there any instructions anywhere? This looks like a fun mod.


    • bill says:

      I’m not ready for this to be a kit–there are some heat issues under gig conditions. Also, the bias supply is marginal for 5881s and requires some additional modifications for more voltage.

      The octal socket upgrade is now available as a kit. I recommend JJ 6V6-S output tubes, but you can run 5881s at your own risk.

  6. Steve says:

    I am getting a blues junior tommorrow. had one before for a short period and remember it being warm. I have only one primary requirement from it. a warm ,articulate, focused jazz tone. My main guitar is an gibson ES-175. I have a “71” fender super reverb as well… and a real nice re-issue fender “57” strat. for blues… I really just want too get a wonderfull jazz tone …. I belive the BJ with some of your mods and a real articulate speaker will be, both portable and tonefull …. can you recommend the way to make this happen… I do not want to worry about “getting that sound” I just want to have it and focus on playing!
    thanx. Steve. M.

    • bill says:

      The basic mods, presence control, TwinStack and Clean Boost greatly expand the range of available tones. You could give that a listen and then decide on a speaker to push the amp in the final right direction. The output transformer elevates the quality of the tone, but doesn’t change it.

  7. Mark says:

    how much would you sell this bad boy for? you have me drooling.

    • bill says:

      Not for sale, at least not yet. I still need to do a little more with the bias circuit and think some more about the heat load, although it’s better with JJ 6V6s than the 5881s.

  8. mike_h says:

    I noticed that you did the high-voltage preamp mod on this amp, and this is a cream board. How many, and which, resistors did you replace?

    • bill says:

      I replaced two power supply resistors, but not the preamp resistors, so this one has stock high gain. I’ve done other versions of this amp with lower gain in the preamp, and it sounds very nice, more Twin-ish or blackface.

  9. bwsettle says:

    I notice that under the description of the new Octal Mod Kit that you say “cream board only”. Will there be a version for the green boards?


    • bill says:

      I don’t plan to do a kit for green boards. There are too many components on the tube board that have to be moved elsewhere when you cut away the sockets. Each “invented” connection is another potential point of failure. Even people who are over their heads have a reasonable chance of making the cream board conversion work, but there are many more ways to screw up the green board conversion.

  10. Patrick says:

    Can I install a Headphone Jack so I can play thru headphones and get the same output settings as those selected for he speaker?
    If so, how would you suggest.

    • bill says:

      Tube amps always need a speaker-like load. So a product like the Weber Headphone Tap or one of their other attenuators with a headphone out would be a good choice.

  11. John L. says:

    Hi Bill,
    Just about finishing the mods but one thing is not clear and no layout came with it. On a Green board, adding the Line-Out and Aux. Jack, the hook up to the Main Speaker jack is not very clear. Do I hook to both Green mounting tabs with the green Aux wire and the Black wire to the inner two upper conections as shown for the Cream board, it looks as if the connections are soldered to two connections each. Thanks……John

    • bill says:

      One lead goes to green and one lead goes to black. You have your choice of places to attach them, but I just stick the aux jack wires into the gap between the pins and the circuit board on the stock output jack.

  12. bob says:

    Hi, the sound file link doesn’t go to sound files. I was wondering if you know that?

    do you do mods for bj’rs for harp players ?

    • bill says:

      I just checked the sound files and they are on the server and they played in my browser. They’re just 128K MP3s, nothing special.

      I do mods for harp, but I haven’t packaged them as a kit because every harp player seems to need a different tone. Some want more distortion, some want clean, etc. Email for more info.

  13. geos says:

    Hey Bill –

    That’s a really cool little “labeller” you have for the jacks and switch. Who makes that?… 3M maybe. I had something like that a good long while ago. But it would not print two lines of print on the same width of tape. IOW, one would have to make two lengths of the label the way you’ve got it. I’d appreciate a nudge in the right direction.



    • bill says:

      I use an old Dymo Labelmaker PC. With the PC program, you can force it to do two lines and some special stuff. Another alternative, if you have a laser printer, is clear label stock. Print anything you want, but put some clear tape over it to protect it from getting scraped off.

  14. Bob Stitt says:

    On your 1000th Modified Blues Jr. there is an impedance switch for 8ohms/4ohms. You also offer a mod. kit for an extension speaker jack which, if I understand correctly, is simply a parallel connection to the existing speaker jack and requires no other mods. (other than drilling the mounting hole). What then is the purpose and function of the 8ohms/4ohms switch on this 1000th mod. unit?


    • bill says:

      If you run the amp hard into a 4 ohm load, an exact match (4 ohm winding on the output transformer) gives you greater efficiency and less wasted heat, less wear and tear on the tubes. If you only play quietly, it doesn’t matter whether you run 4 or 8 ohm loads–the tubes don’t work hard enough for it to matter. So you would use the TO22 for the most demanding applications where you run a 4 ohm load. For occasional 4 ohm operation, you can use the TO20, which is simpler to install.

  15. Steve Austin says:

    On your BJ tube mod you use 5881’s or 6V6’s. What would be the problem using the larger 6L6’s? Internal differences, clearance issues or heat build up? I know I can order a Hot Rod Deluxe sized cabinet set up for a BJ chassis which would take care of clearnce issues and further enhance the overall tone. Is this something that would work, much like it does in the Deluxe Reissues with the 12AX7 and 6L6 configurations? Thanks for all the tips you give us and work you put into the site.

    • bill says:

      6L6s run hotter, require more plate voltage than the BJr can supply. It also can’t supply enough negative bias voltage without rebuilding the bias supply from scratch. The larger cab wouldn’t do that much for tone. If you’re going to go with a big cab, just go with a Blues Deluxe or Hot Rod Deluxe.

  16. Joe says:

    Bill, what mic did you use on the 1000 dirty bassy Blues sound bite?

    • bill says:

      I used the stereo T mic on my M-Audio Microtrack recorder. It wasn’t particularly close to the amp or anything, maybe 4-5 feet away.

  17. mike says:

    hi bill..running 5881’s in the bj..realisticly is it possibly to run them 100% of the time.. practice/live at all different levels and have no problems? what is the longest test you have done on them..longest time you have had them in one amp?


    • bill says:

      One of my customers runs with them all the time and reports no problems. A couple of other customers use them all the time, too. Some have had concerns about them running hot and have switched back to 6V6s. The risk is up to you!

  18. mike says:

    hi bill..concerns or was there an actual problem..and what would be the first thing to be damaged?

    thank you

    • bill says:

      No actual problems that I’m aware of, just hot-running tubes and hot-running power transformer.

  19. Bird Dog says:

    Howdy Bill, I just finished performing several of your mods on a Blues Junior for a customer of mine. Thanks for the concise instructions and complete parts set…everything went well and the amp sounds very good. 3 of the mods were the installation of 6v6 tubes, an adjustable bias control, and the Heybouer Output trannie. I set the bias according to your instructions (to 4.2 volts difference between the red center tap and the brown plate connection.) My question is: when I checked the current draw on the tube by the transformer shunt method (I have been using this method for a very long time) I read 42 milliamps current draw at the plate, but the tubes appear to be operating well. My normal setting for a 6v6 running at 355VDC would be around 23 or 25 milliamps. When I tried to use the adjustable bias control I got little reduction in the current reading. Is there something about the Blues Junior circuit which renders the transformer shunt method of biasing inaccurate? Thanks for your time, I know you are busy. Bird Dog, Bird Dog’s Music House

    • bill says:

      But the BJr only has around 320V on the plate, so the current has to be higher. If you were reading 4.2 volts across the brown-red leads, that’s actually 31 milliamps across 133 ohms, or about 10W idle. A little warm, but not bad.

      If you jumper R51, the 5K resistor, you’ll have a few more volts and can turn the bias up a little higher.

  20. Richard Bonn says:

    Hi Bill, getting ready to order some upgrade kits for my cream board BJr. But was curious about the octal power tube socket kit with the 6v6s’. What exactly is involved workwise installing this kit ? Couldn’t find any info on the site. Just want to make sure that I don’t get in over my head on this one.

  21. Joe says:

    hey bill ,did the octal conversion wow!…my question is about bias for 5881s .. is it the same as the jj6v6 w/ the t020 ot across red / brown?

    • bill says:

      For 5881s, turn the bias up all the way and hope for the best. The BJr’s bias supply voltage is marginal for 5881s. They won’t redplate, but they’ll run on the hot side. You may want to consider eliminating R51 (jumpering it) to make a few more volts available.

  22. steve bratton says:

    hi bill
    im in the process of installing an extention jack socket to my pro junior
    what do i exactly need & have to do to do this ?
    do you recomend taking off the negatve feedback loop on this amp ?

    many thanks
    steve ( stevierayb fender forum )

  23. steve bratton says:

    thanks bill – & your right about the NFB !

  24. Joe says:

    hey bill… im running jj 6v6s in my junior one of the many billm mods ive done theyre biased pretty warm as you suggest 32-33 ma(across 1ohm resistor).. i was going to try the tunsol .before i put them in i wanted to cool off the jjs …the lowest i could get was 31.9 per tube before bias pot was maxxed..i was thinking 26-30ma will get me closer to the 60-70% range @ 325v…do i need to change out the r51 resistor? if so what value ?what do you recomend? thanks so much for your help …joe

  25. ChristpherBrian says:

    Hey Bill is there NO chance you will develop a mod for the green boards so I can run this setup?

    • bill says:

      You could use the cream board kit to do the mods to the green board, but you would also have to preserve the LED power supply on the tube board, move the filament balance resistors to the main board, and move the anti-flyback diodes to the tube sockets. There are far too many ways for people to screw up those additional mods, so I don’t support them. There would be too many broken amps and unsuccessful outcomes.

  26. F p says:

    Bill, would consider offering a Full Blues Jr kit with all your mods? perhaps with your own chassis, transformers, boards, tubes, speaker, cabinet? You pretty much changed the whole platform already. It would be interesting and I know for sure it would be a really nice amp.
    Thanks for all your tips and hard work


    • bill says:

      Not likely that I’ll be offering my own brand of amps any time soon! There are still many thousands of Blues Juniors to be modded. And there’s already too much competition in the boutique amplifier category.

  27. alecaster75 says:

    Hi Billm I`d like to know your opinion on the Eminence Man O War for blues junior.

  28. pschmalzer says:

    Hi Billm,

    Have you ever tried adding a switch or control to lower the output wattage to say, half or even a quarter of the regular power? I love the sound of my Blues Jr with your mods but I can’t really open it up in a ‘bedroom’ environment.

    • bill says:

      Half-power switches don’t work very well. They sound muddy. Use the master volume–that’s what it’s for!

  29. NEDiver2 says:

    Hi Bill:

    I know you have been very busy, but am wondering if you’ve come to a decision as to whether the stock BJ power transformer is large enough to handle the 5881 tubes or have found a replacement power transformer that will do the job?

    Thanks in advance and as always keep up the excellent work.

  30. dr1020 says:

    When biasing my Blues Jr. after completeing 6V6 mod, I could not get bias to -4.2v.I jumpered R51 and now the bias does not change at all. It is stuck at -2.8v. R51 on my amp was not 5k it was 33k. I double checked all of my work and it all looks good. Do you have any ideas of what could be the issue?
    Thanks, Kevin

  31. dr1020 says:

    I removed jumper from R51 and installed 5.6k resistor. Now I can get -4.2v for bias. The amp sounds incredible now.

  32. dkt says:

    Can you upgrade to the 6v6 tubes with the stock output transformer or do you have to have the upgrade OT. The blues Junior has a 12″ speaker and the Princeton only a 10″, but the Princeton has very rich bass. I can turn the bass all the way down on the Princeton and still have plenty, but the blues junior is not the same even with the bass turned all the way up. I would think they would use the same OT since they are both around 15 watts. I had assumed the difference was in the tubes 6v6 verses the EL84. I want the Princeton tone from the Blues Junior. What do I need to get it? The basic mods (tonestack), or will it require the 6v6’s or something else.
    Thanks, Dennis

    • bill says:

      The difference is that the BJr has much smaller coupling caps and smaller tone caps than the Princeton Reverb. The BJr was designed for higher, Marshall-like overdrive, a thinner, more raunchy sound. The basic mods kit makes a world of difference and brings the coupling caps and tone caps more in line with traditional Fender designs. The larger output transformer further improves tone quality. The 6V6s have larger plates and do a better job with bass than EL84s, but the majority of the improvement comes from the basic mods.

  33. leslie says:

    Hi Bill, I did the 6v6 conversion on my blues jr. yesterday. sound’s great! But the 5881’s sound a lot better!! WOW!!!I just want to make sure about the bias,…..I can just put the 5881’s in ther without doing anything to the bias??….They sound the way I like it right now!!WOW!!!…Thank’s for all your advice and your mod’s! Have a Great day and Thank’s again!!

    • bill says:

      You should check the voltage drop across the OT primary. Chances are you’re in an acceptable operating range, but you’re still on your own because the tubes draw so much filament current. They’re putting maximum load on the power transformer.

  34. leslie says:

    Thank’s Bill!! Can I bother you and ask how much it should measure?

    • bill says:

      Ideally, you’d want around a 7 volt drop. That’s probably not possible with the bias voltage available, but also not a problem because the 5881 is not highly stressed.

  35. JimmyHaggard says:

    The 6v6 conversion kit worked like a charm. I used JJ 6v6S matched pair (33). I went with a fixed bias change instead of the adjustable bias, by changing one of the bias resisters to 470 ohms (i think is was r51). The bias voltage is now -26 and some pocket change. After installing the 6v6 tubes, I installed a pair of tube clips to hold the tubes in place (very easy to install and I highly recommend the clips).

    The sound is excellent!!!! It is much different than the sound with the 84s. The slightly shrill edge is gone. The bass is firm and full. The overall sound is BIG and FULL and RICH!! You could call the amp a Blues Supreme now, cause it ain’t Junior anymore. I had a metal label made for mine, “Blues Boutique.”

    I have done a lot of the other mods suggested by Bill (bought parts and did them myself before the kits were available). I backed out one mod because it increased the bass too much for my ear (went with an upgrade CAP though). I also installed a Mercury (made in the USA) output transformer and put in a Celestion G12H Anniversary speaker. One last thing to do is install the standby toggle switch mod.

    Thanks for your suggestions over the years Bill.


  36. leslie says:

    Bil, you’re not gonna believe this! I got a set nos ge 6l6gb blackplate tubes and I’m able to get the voltage drop below 7 volt’s.Sound’s wonderful and I only gave $50 buck’s for them 🙂 Thank’s for all your advice and mod’s.I’m glad I did this mod!!…..Thank’s…….

  37. steve leblanc says:

    hi, i m really impressed with all your mods. i have myself a cream board blues junior. i want to improve the tone but i really want to make it louder. what is the easiest way? i m not sure about cutting fiber glass. i m not a pro in eletronics. thank you.

    • bill says:

      There are limits to how much loudness you can get out of an amp. The easiest is a more efficient speaker. The Eminence Swamp Thang and Wizard are two of the loudest affordable speakers. Adding a second speaker gets you almost 3dB more. Going to bigger tubes helps, but even doubling the power only gets you another 3dB. But you get different tone, more headroom, and a much more muscular “feel” to the amp.

  38. steve leblanc says:

    is the italian jensen c12n louder than the stock one? is the basic mod an easy one to do? thanks again.

    • bill says:

      The Jensen is about the same loudness as the stock (Eminence Special Design) speaker, but it’s brighter, so it cuts through band clutter pretty well. The basic mods require skill with a soldering iron, soldering on printed circuit boards, and working with hand tools.

  39. Wil says:

    Hi Bill,
    Since I changed my speaker (Eminence GB128 101db to WGS G12C 96db) I’m missing some power. I’m thinking about doing the octal conversion mod but i’d like to run 6l6. The problem is that I live in Belgium… So the 120v TP24 won’t fit. What would you do to reach about 22w ? Or 30w if you have another solution !
    Thank you !

    • bill says:

      Sorry; I don’t have a solution other than using an external step-down transformer. The octal conversion with 6V6s and the TO20 or TO22 will give you a small increase in power, but not nearly enough to compensate for the 5dB loss from changing speakers.

  40. Geeeeorge says:

    Hi Bill

    I”ve finished upgrading my amp at is superb!

    I did the following:

    First I trimmed the posts the knobs all attach to, then did the twin stack, basic kit, high volt preamp mods, and presence knob. Then I did the TO26, TP24, octal kit and the bias mod to go with the octal kit.

    I cranked it up at band practice the other night with an extra 12inch cab and it was AWESOME sounding and LOUD.

    The clean sound is the best i’ve ever heard, the amount of bass is fantastic, and it has great character. and openess to the sound. I’ve had a few amps over the last 15 years and this is without a doubt the best sounding , as well the lightest and most portable.

    The basic mods seem straightforward enough to install for anyone with basic mechanical/electrical repair experience, but i’d caution anyone considering the octal conversion that its a bit more advanced. You need the right tools and a bit of experience using them.

    Luckily Bill answered lots of questions for me by email as I was working on it.

    Thanks for all the work Bill!

  41. Henrik says:

    Hi Bill
    I just switched tubes from 6V6 to 5881 without changing bias and got a 8.6 volt drop. The sound is just amazing, but is it safe to run at this voltage drop? Between which voltages would it be OK?

    • bill says:

      That’s pretty hot. The tubes can probably take it, but I would knock it down to no more that 7V drop.

      • Henrik says:

        After playing the amp a while with 5881’s I definitely decided to keep them in for good. So I’ve biased now at 7V and the amp stays pretty cool even after hours of jamming, only the tubes themselves get a little hot. And it sounds just fantastic, almost hard to believe from this little amp, very touch sensitive. 6V6’s are really nice but 5881’s are a completely different thing.

  42. PeterM says:

    Dear Bill,

    Just wondering your thoughts about attenuation. What do you think is the best, and safest mode of attenuation for a Blues Jr Tweed? I don’t necessarily mind if the tone is affected a little (as it’s for bedroom usage), but I am more worried about it being safe for the amp. Your thoughts are much appreciated.

    Kind Regards

    • bill says:

      I dislike attenuators. They make the amp run hot and they don’t sound that good. Between the master and volume controls, you should be able to get cranked tone (if that’s your goal) at bedroom levels. The audio-taper master volume makes it easier to dial in low loudness levels.

      • PeterM says:

        Thanks for the audio-taper tip, the controls do get too loud too quickly. However, having the master cranked driving the power tubes does warm things up and sounds nice to my ears, instead of just having the preamp tubes being driven hard on their own.

        I have a local tech who is very much in agreement with you and suggests a possibility is to find a very large pot to be placed between the amp and speaker….

        • bill says:

          Heck, if it’s only for practice at home, you really don’t need power tube distortion. And your amp will be much happier for not being under heat stress.

  43. RickinVirginia says:

    Re Geeeorge’s post above, “Luckily Bill answered lots of questions for me by email as I was working on it.”

    Any chance of posting your email correspondence regarding mods, or maybe a synopsis of the questions and your answers? I’m thinking there’s a lot of valuable info there that many of us could benefit from. And my apologies if these are posted somewhere on the site and I’m just too dumb to find it -;).

    • bill says:

      Most people don’t have many questions. The installation is fairly straightforward if you can do the requisite drilling, cutting, and soldering.

  44. andrewmsprague says:

    Bill, I have a completely stock Blues Jr. and am not impressed with the sound of the EL84s. Would it be safe to use 6V6/EL84 adapters rather than resoldering octal sockets onto the board? And would they perform well without replacing the output/power transformers? I love the deeper bass response of the 6V6 based Fender amps. I do plan on doing the basic mods to help open the amp up. I don’t like the thinner, raunchier sound of the overdrive.

    • bill says:

      The EL84s are not the limiting factor. Most of the “missing” bass is lost in the tone stack and coupling capacitors. The basic mods kit will do the most to restore the missing frequencies and give you a much broader range of adjustment. 6V6s need a different bias voltage, and it’s not adjustable in the stock BJr. I think you may be pleasantly surprised at how good the EL84s sound after the the basic mods and a better output transformer.

      You can always upgrade to 6V6s after the fact if you want. The big plates on the JJ 6V6s will open up the bottom end a bit more. The octal conversion kit includes different screen resistors and coupling caps to run the 6V6s properly.

      • andrewmsprague says:

        Thanks, I’ll try that. I just tend to prefer the bigger bottles. Thankfully I have the cream board so the octal conversion kit is something that is available to me, if I decide to try it.