Update 4/27/19:

Due to popular demand, Hallman Labs finally have a few sound clips of my amplifier. This is the Blues Jr, combined with some of my custom pedals and of course, my Schecter Tempest Custom guitar. My friend, Kale Brown, helped me out and played my guitar, while I did the recording (mostly on a Tascam DR-05). The results are pretty good for what we put into it!

Pedals used at some point in the recording:

Boss RC-3 Loop Station, BYOC 2 Knob ESV Bender, Custom Crybaby Classic w/ Whipple Wah, MXR Uni-Vibe, TC Electronics Hall of Fame Reverb.

All wire for guitar/amp/effects pedals were Mogami 2524 with Neutrik plugs.

Note: We had a baby asleep in the house we were recording inside of, so we could only go so loud. I’ll try to add a better clip highlighting tube breakup/distortion at a later time. Other than that, Kale does an excellent job at showcasing this amplifier.

Tubes Glowing 1

The only bit I captured with my Nady CM-100 + Rolls Mini-Mic Preamp -> XLR to USB

You can pick up on more detail in this recording than the rest, especially the high end.

Lighter playing (DR-05):

Louder playing with some breakup (DR-05):

Variety with a little talking (Crybaby Classic Wah Pedal, MXR Uni-Vibe) (DR-05):


Update 6/25/18:

I was a little worried about my modded Fender Blues Jr. I added some Siemens (EPCOS) filter capacitors and ELNA SILMIC-II into the signal path locations. I also put some vintage orange drops in to go with the newer ones.

After I finished installing everything I had no sound.. The tubes were heating up and I had voltage across the main PSU cap. I re-flowed any questionable solder joints and stuck with it. After 2 days I had her singing again!

Tubes shown:
2x 1961 Siemens EL84 6BQ5 rX3 (Tested 130%)
2x 1963 Sylvania 5751
1x 1961 Sylvania 12AY7

I really like the tone I have now, love my Celestion G12-H Greenback speaker with these mods.

(For the curious, the two potentiometers separate from the rest, are the sparkle and presence mods from BillM)

Celestion G12H 55

This is from my thread on TDPRI, which can be found HERE, if you’d like to see the topic in its original entirety.

Most of this is copied and pasted from there because it was already so detailed and accurate to what is being used. My memory isn’t as good as the Internet!

Mainly this was my first venture into modding audio circuits, besides building BYOC (electric guitar effect pedals) kits and selling them.

Working with an amplifier and doing mods is so much fun, hearing the differences you can make is very rewarding. I encourage all readers who own a Fender Blues Jr. to try the “basic kit” BillM sells for all versions of the modern Blues Jr models, and the Fender Excelsior.

2021 Correction: BillM passed away a few years ago sadly. A year or more after, I asked his son for permission to carry on his tradition (hoping to replicate his circuits, which I could do already (but I won’t out of respect)). He did not yet give me permission. I have my fingers crossed, but don’t hold your breath. I understand whatever he decides and I wish him and their family all the best in the future. I know that Bill will be looking down over them and keeping them safe.

Article on “BillM”‘s Fender Modding site announcing he is back and working on a backlog of orders:

Hi, all! I am back to the grindstone. I have about two or three billion emails to answer, so if you’ve sent one in, I’m almost there. Meanwhile, the webshop is back up and running! Thanks to everyone!


This is great news for all current and future Fender Blues Jr owner’s! I believe the two or three modern versions of the Blues Junior (made in last 20 years) is the best trade off between tubed audio circuits and their solid state equivalents. BillM and his son create some of the best Fender Blues Jr (“BillM”) mod kits for your money.

Most mods for tube based electrical equipment will run at quite the premium, if for nothing else, due to LETHAL currents & voltages being present. Without taking the proper precautions, doing a capacitor upgrade could end with your obituary, seriously. That isn’t a joke and this is why BillM does an excellent job instructing the customer how to build and/or install their kits. The main thing is to make sure you bleed any voltage off that is currently across the primary power filtering capacitor/s (applies to all amplifiers), before doing anything on the amplifier. Those filtering capacitors can generate lethal spikes of current, so do not even think about skipping that step.

You can find Bill’s Guide on bleeding the power capacitor/s here.

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I purchased the Blues Junior knowing it was pretty much the perfect practice/home amp in the sub $500 range for that classic American tone. After spending some time with it and stumbling through the internet to BillM’s website (http://billmaudio.com/wp/) I decided to start modding the amp. I have a long history of modding PC’s, so I knew this would be a piece of cake with how simple the Blues Jr. is, circuit wise.

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I started with some basic BillM mods, this is the list of mods I purchased/installed:

  • Clean Boost Mod
  • Basic Cream Kit
  • Sparkle Mod
  • Presence Mod
  • Switchcraft Input Jack
  • Switchcraft Line Out Jack
  • Standby Switch
  • TO20B Upgraded Output Transformer

After installing all of those mods I was very satisfied with the tone. The only thing still lacking was the bass response from the stock speaker

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At that moment in time the “budget” wasn’t the main concern and you are talking about a $200 speaker upgrade (that could be moved or sold at very little loss).

Here is a breakdown of everything you see in the completed pictures:

Blues Jr. – $429
NOS Tubes – $105
BillM Mods – $91
Speaker – $199
Total – $824


I went with the Celestion G12H Greenback because I have heard them compared to some other 12″ speakers. Nothing else that Guitar Center had come close to that G12H tone. Looking back, now I wish I had gotten a used Blues Jr (since I was going to void the warranty anyway), but you live and you learn.

Build Log Comments:

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I just got done installing the BillM Clean Boost board + Stereo Foot Switch mods and I am really impressed with that mod. You can really hit the output tubes hard and this is something no pedal can do going into the front end (no matter how expensive it is). Next to the basic kit, the clean boost is my favorite mod out of all of the BillM mods. The only possible thing left I can do now is change transformers and output tubes, but I like the EL84s. Now if we could put EL34s in it, that would be a different story.

All NOS tubes and the famous G12-H/G12M Greenback (Heritage) speaker by Celestion
One of the first pictures I took of my totally stock Scheter Tempest Custom and Fender Blues Jr.

You can see info on a mod I did to the Tempest Custom here.

The NOS tubes do create a tonal difference vs. the stock Fender Groove Tubes. My only issue was that I made so many changes so often and that made it hard to pin down specific improvements. However, I know for sure the NOS EL84s (GE USAs) created a much more pleasant glassy sound than the Groove Tubes. I also went with one 12AY7 (in the V1 slot) to create more clean headroom, this is a very easy tweak anyone can make. Keeping in mind that with my BYOC ESV 2 Knob Bender, I can enter Jimmy Page land at the click of a switch (even with a 12AY7).

I went ahead and changed out tubes V2 and V3 because I figured I might as well go all NOS, however, I did not spend near the money on those as I did on the 12AY7 (V1) and the two power tubes. Although V2 is a GE USAF 5751, but I didn’t pay very much for it compared to the V1 12AY7. So, I’m running all GE US Tubes except for the Sylvania in V1. Fun fact, from my understanding, the Sylvania 12AY7 may have been made in the same plant as the GE tubes!

My EL84 GE Power Tubes that tested 7500 and 6800

My Sylvania 12AY7 that test perfectly balanced

My V2 and V3 12AX7s: (I got that one GE 12AX7 for $9.99 because for some reason there were no other bids, even though it was tested (U GETTER/ GREY PLATES- 52/54))

Overall, from everything I did, my favorite mod is the clean boost + stereo foot switch. Being able to push output tubes harder, from a completely transparent boost, is something that no conventional pedal is going to achieve. No matter how expensive it is, because traditional pedals run into the front end of the amp and push the pre-amp tubes, not the power tubes.

When comparing pre-amp tube breakup/distortion to power tube breakup, pre-amp is harsher and not as agile as the EL84 breakup. I still need to get some more pictures now that I have the Clean Boost installed and I have the line out mod in there now also. If anyone has any questions about anything or wants to tell me I am an idiot for spending so much on a Blues Jr. (again, lol), just leave a reply or use the contact me tab. By far the biggest tonal difference was when I installed the G12H (perfect balance all around and a true vintage sound), that was $200 well spent. I know I will never get rid of that speaker, if I upgrade amplifiers later down the road, the G12H will move also.


17 thoughts on “Fender Blues Jr BillM Mods (Custom) – Updated 8/25/19 Sound Clips Added

  • Andre

    Hello, I have a Fender Blues Jr American, I am thinking of making a modification, change the source and the output transformer by one of a 30W, swap the sockets and put valves 6L6 JJ Tesla, so that has more headroom, then put 12AX7 of the Tung sun and in sequence , put a Texas Heat Eminemce. Will it be okay?

    • Andre,

      Yes, that should do great in your Blues Jr! I highly recommend using BillM if you weren’t already planning to do so. He sells a great octal conversion kit ($25), the matching transformer and an octal specific biasing board ($19) are all available there. You can see all of his mods here: https://billmaudio.com/wp/?page_id=65

      Be sure to read all of what BillM says, with regard to the octal kit and selecting a transformer, it will save you some headache. (Or just contact him directly for a specific question)

      If there are any other questions you may have that you think I can help you on, please don’t hesitate to ask!

      Thanks for commenting on my article!


      • Tim Ryan

        Great information. I did the Bill M mods to my BJ tweed several years ago. I didn’t change out the speaker but was looking hard at getting the Celestion you have. The other change I would like to make are the tubes putting in the NOS tubes. I’m planning on doing that here in the next month.
        I went to Bill M’s site and it doesn’t seem to be working. I know Bill passed in 2016 and his son, Andrew, was running the business. Since it’s been a few years, do you know if Andrew is still doing the business?

        • Hey Tim!

          Thanks for checking out the site and for the kind words! 

          As far as I was aware, BillM is still alive. I could be wrong though, do you have information that he passed? 

          I know he was sick years ago, but they posted an update, implying Bill was back at it, which I quoted in this article (when he posted it).

          His son filled the orders for a while, but I was not aware that their site is down. I did a little research on the domain, using Archive and it looks like BillM has been down since somewhere in Q1 of 2020. 

          The last time that Archive did a successful backup of the site, was on Dec 29th 2019.


          Let me try to contact them directly and get back to you, I have Bill’s direct email. 

          If Bill has passed and his son is not interested in continuing to offer these mods. I will request permission to start producing them myself. BillM’s Clean Boost is one of the best guitar amp mods for under $50, that I have ever come across. I’d definitely be willing to make and sell those boards, if I can get permission.

    • That isn’t an amplifier that I have experience with. However, the clean boost should work in a similar amplifier. The problem is finding those clean boosts by BillM. The site no longer offers them for sale and I couldn’t get permission from BillM’s son to produce them myself.

      You can certainly upgrade the transformer/s, but I’d do research into what others with that amplifier are running. Different designs will have different voicings and the desired tone will decide your selection.

      Sorry I couldnt be of more help, but my experience (for modding guitar tube amps) is solely with the Blues Jr.

      Good luck and if you think I can help with something, feel free to reply back!

      Thanks for checking out the article!
      – HL

    • Hey Larry, thanks for stopping by!

      Sadly, I do not have permission to sell BillM’s clean boost, at least not yet. I reached out to his son, following Bill’s death, but have not heard back.

      If I see enough interest in this, I will create my own custom version. The boost module is really not a difficult circuit to make and with just a few changes, I think I can improve on Bill’s design.

      Thanks for checking out the site!

  • Mark Elam


    Hi. Great article!

    As you know, Bill M is no longer with us and it seems his mods are no longer available. I used the Fromel supreme kit. Also have a Heyboer TO-20 output xfmr, Eminence Cannabis Rex speaker, JJ tubes with 5751 in the V1 position, MOD reverb tank. Amps sounds a LOT better, very controllable, nice to listen to, except… it still sounds boxy. Considering a Mojotone cabinet.

    Your thoughts?


    • Hey Mark!

      Thanks for checking out the website.

      You have a lot of the best mods already installed, so if you are still not satisfied with the overall signature, changing the cabinet could be a good move.

      However, I’d recommend you add a line out jack (BillM had a Switchcraft kit, it’s really simple), then you can utilize a second speaker cabinet. This will prevent you from having to alter the stock enclosure (maintaining the convenience of the Blues Jr), but will still give you the benefit of an upgraded speaker and cabinet.

      Please let us know how it goes, changing cabinets is something I haven’t looked into myself, so I am interested how it goes for you.

      Take care,
      Keith H.

      • Mark Elam

        Keith, thanks for the reply! I went ahead and ordered a cabinet from Mojotone. Pine construction and slightly larger dimensions. A different resonance. I’m sure it will be an improvement, but I’m looking for a particular result. Lead time is involved. When I’ve made the swap, I’ll get back with you.

  • Jay Mendoza

    My Blues Jr makes a high frequency feedback noise , about 3000 Hz, with nothing plugged in and all the knobs at 6. I put a 100pf across R19 (green board) and it did not help.

    • Jerry Helm

      Sometimes the blue lead from the output transformer crosses the ribbon cables to the power tubes too closely, causing a parasitic oscillation. Push the ribbons down and pull the blue transformer lead away some, The fix is free if it works, and it does happen sometimes.

Join the discussion and let HL know what you think!

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