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Fender Blues Jr BillM Mods (Custom) – Updated 4/27/19 Sound Clips Added

Update 4/27/19: Due to popular demand Hallman Labs finally has sound clips to offer of the amplifier. This is the Blues Jr, combined with some of my custom pedals and of course my Schecter Tempest Custom. My friend Kale Brown helped me out and played 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.

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:

Was a little worried about my highly modded Fender Blues Jr. I added 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!


Sorry about the cell camera, sometimes it’s just easier to go with one.

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

(For the curious, the two potentiometers hanging 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: Click!

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 better than most of the mods I have done! Hearing the differences you can make is very rewarding, especially when you are doing all the building yourself. 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.

Correction: BillM IS no longer providing his mods again, after a hiatus that he took due to health concerns. For a while his son filled the orders, but on their site it sounds like Bill is back at it again. I may reach out to him and see if he wants to team up and let me be the guinea pig for any new mods!

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

“We’re Back!”


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 (sometimes superior) solid state equivalent. BillM and his son create some of the best Fender Blues Jr (“BillM”) mod kits for your money by just about any other modern and vintage based guitar amplifier, not counting complete DIY kit amps.

Most mods for tube based electrical equipment will run at quite the premium if for nothing else, LETHAL currents & voltages present in multiple places… Without taking the proper precautions, doing a capacitor upgrade could end with your obituary, seriously. That isn’t a joke and 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 in the power caps.

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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 onto BillM’s website ( I decided to start modding the amp. I have a long history of modding PC’s (even directly soldering on motherboards and video cards along with building custom guitar effects pedals. So I knew this would be a piece of cake with how simple the Blues Jr. is.

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

  • 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 what I had in this is the list of mods I purchased/installed from Bill Ms with all the mods. 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 here 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 (lol ever listened to Hendrix? ) versus some other 12″ speakers and nothing came close to it in my mind (from what I’ve heard in person). 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 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 transformer 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
Schecter Tempest Custom w/ (genuine) Seymour Duncan pups

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.

The David Allen-designed TO22 Heyboer output transformer

Low Profile TO20 Output Transform


Premium TO20B Output Transformer

TO26 Output Transformer for 6L6 Conversion

TP24 Power Transformer

From all these options I think the Low Profile TO20 Output Transformer is my best option, as I don’t intend on running an auxiliary cab (i.e. additional dedicated speaker cabinet). However, I think based on what I have already done to this amp, this mod is a must to round it out. I was correct on that assumption and I haven’t touched the amp since the day I put in the output transformer because it is such a strong amp now. It is well worth the ~$900 price-tag without a doubt (to me). These were some of the most successful mods I have ever done on any hardware.




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3 thoughts on “Fender Blues Jr BillM Mods (Custom) – Updated 4/27/19 Sound Clips Added Leave a comment

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