Mod Kits and Services

Yes, we will mod your Blues Junior.

We can install all of the modifications below. All you have to do is remove the chassis and mail it to me. Please email me at billmaudio@gmail.com for up-to-date prices, instructions on removing the chassis, and packing it for safe shipment.

And we have great, time-proven kits.

We have all the kits you need for a great-sounding Blues Junior, with parts selected for quality and performance. They come with photographic instructions and we’ll support you. You should know how to solder on printed circuit boards and be comfortable with basic tools and wiring.

The cart buttons automatically calculate domestic mailing, and we are currently testing weight-based international shipping. If the charges look wrong to you, email me and we’ll figure things out.

The US Post Office has recently changed procedures for International First Class mail, making it necessary for me to switch to International Priority Mail. It is more expensive, but it’s faster and it provides tracking numbers and better information for Customs.

I always have a considerable backlog of orders to work through. It may take one to three weeks for me to fill your order, but be assured that it will get filled. Writing to ask “Where’s my order?” just slows me down.

Thanks for your understanding.

- Bill

Here are the kits:

Basic kit, cream board: $22

Everything you need to eliminate that boxy sound, take the harsh edge off the distortion tones, add back the “missing” lowest octave of bass and sweeten the clean tones: Orange drop tone stack and coupling capacitors, adjustable bias trimpot, power supply stiffening capacitor, even a #59 high speed steel drill for a professional job installing the adjustable bias and power supply stiffening cap. (It’s just a couple of small holes; a fresh, sharp drill makes it easy.) The adjustable bias is a high-rel, precision, sealed, 25-turn trimpot for setting your bias accurately. The power supply stiffening capacitor doubles the size of the main filter stage, halves the ripple going to the output tubes, and provides solid bass tones that you’ll notice right away. The cream board has been produced from 2001 to the current, Blues Junior III. If you’re not sure, remove the back and look.


Basic kit, green board: $27

Everything you need to eliminate that boxy sound, add back the “missing” lower octave of bass, take the harsh edge off the distortion tones, and sweeten the clean tones: Orange drop tone stack and coupling capacitors, adjustable bias trimpot, a power supply stiffening capacitor, even a #59 high speed steel drill for a professional job installing the adjustable bias. The adjustable bias is a high-rel, precision, sealed, 25-turn trimpot for setting your bias accurately. The power supply stiffening capacitor doubles the size of the main filter stage, halves the ripple going to the output tubes, and provide solid bass tones that you’ll notice right away. The green board kit also includes a new reverb coupling capacitor and resistor to overcome the hum- and noise-prone reverb circuit on the green board. The mod updates the reverb so it performs identically to the current cream board.  The green board was produced from 1995 to part of 2001. Remove the back to be sure.


Presence control: $12.

The presence control affects mid-high frequencies and gives the amp more (or less) bite, as shown here: The Presence Control page. It uses Mogami low-noise coaxial cable to connect to the circuit board and requires that you drill a 9/32” (7mm) hole in the face panel below the Fat switch. Despite the drilling, I highly recommend this mod—it will give you outstanding control over the amp’s aggressiveness, going from hard-edged to mellow. The control has a built-in pull-up switch for the optional Clean Boost.


Sparkle Control: $12

The Sparkle Control makes the amount of sparkle reduction adjustable from zero (stock Series III) to the same as the series II, to even darker, like the old green board (1995-2000) Blues Juniors. When you pull up on the knob, it defeats the control and gives you the stock BJr III amount of sparkle. You can make a Series III sound like a series II, a Series II (2001-2010 cream board) sound like a Series III, and either of them sound more like the old 1995-2000 green board. It will also brighten the green board, giving it a high-end sheen that you didn’t know was there. Requires drilling, mounting on the faceplate, like the presence control. See the Sparkle control page.


High-voltage preamp mod: $5

Brighter, crisper tone, better headroom for only $5. This mod replaces four resistors in the power supply and preamp and brings the voltages up to a more typical Fender Blackface level. Highly recommended for green board amps. It works for cream boards too, especially if you’re looking for a brighter tone with more clean headroom. The tone is more “dry” on the cream board, which isn’t to everyone’s taste. Not recommended with the TP24 power transformer.


Switchcraft all-metal Input Jack: $10

Select board type:

You can replace the plastic input jack with an all-metal Switchcraft jack (the industry standard). It comes prewired with Mogami low-noise coaxial cable and includes two Switchcraft isolation washers (one flat, one shoulder washer) to eliminate the possibility of ground loop hum. Requires removing the circuit board and desoldering the old jack with desoldering braid or a solder sucker pump. The green board version bypasses a noise-prone portion of the circuit board.


Audio-taper master volume or reverb control: $10




Hate the way the master volume gets too loud too fast? An audio-taper control solves the problem, and makes the loudness smooth and progressive. It’s especially good when you’re trying to play quietly at home. The same audio-taper control also works well for the reverb. It extends the range in the same way, making it smoothly progressive at the low end, so if you’re always stuck between too little and too much reverb, it’s an easy fix. This pot does not replace the volume control, only the master volume or reverb. See how to replace snap-in pots here: Replacing Snap-in Pots


The clean boost module: $45

This is a one-inch square board that connects to your circuit board (held by one of the mounting screws) and connects to the circuit board in three places. All connections are from the top of the board; no need to remove it. It gives approximately the same increase in volume as the Fat switch, but without the increase in bass. It makes clean or distorted tones louder, and when used in conjunction with the Fat switch is about twice as loud. It does not increase distortion unless you’re really playing loud. It is usually controlled from the pull-up switch built into the presence control, or, if you wish, on its own footswitch. See the Clean Boost Module page.


Stereo footswitch jack for Fat and Clean Boost control: $8

The Clean Boost is normally controlled by pulling up on the presence control, which has a switch for that purpose. It can be wired to come on with the Fat switch, but the overall volume gain is generally too large and not recommended. An alternative is to change the footswitch jack to a stereo jack so you can plug in a 2-button footswitch with a stereo plug. The footswitch will work in conjunction with the presence control switch and overrides the presence control pull-up switch when you plug in the footswitch.  Order in conjunction with the Clean Boost so I can put a longer wire on the Clean Boost to reach the jack. Newly revised kit is easier to install. You would then use a 2-button footswitch with a stereo plug to control the Fat and Clean Boost separately. Some footswitches that will work with the jack are here: Footswitches for Clean Boost/Fat Option


The David Allen-designed TO22 Heyboer output transformer

Which amp?

works great in a Blues Junior, rounds out the bottom end, increases smoothness throughout the range. My version comes with the leads trimmed to length, push-on connectors installed, and an aux speaker jack that automatically switches to 4 ohms when you plug in the second speaker.  It’s partially prewired, also with push-ons. Requires drilling a #38 hole for the mounting screw and a 3/8 inch hole for the aux jack. Choose this transformer if you intend to run an auxiliary speaker or a 4 ohm load often. The basic mods are essential to get the best performance from this or any other upgrade output transformer. $65.


Low Profile TO20 Output Transformer


Which amp?



This brilliant, all-new design is a collaboration between me and David Allen of Allen Amplification, built to our specifications by Heyboer. It fits exactly into the stock mounting holes of the Blues Junior (also the Princeton Reverb and Super Champ XD and X2), and requires no drilling. The Excelsior has slots that accommodate the TO20. The low-and-wide core design provides all the heft and performance of the TO22 transformer above, but clears large/deep speakers such as the Eminence Wizard or Swamp Thang. The output impedance is 8 ohms. Choose this transformer for ease of installation, great performance and occasional use of a 4 ohm external load. For the Blues Junior, the basic mods are essential to get the best performance from this or any other upgrade output transformer. $59.


New! Premium TO20B Output Transformer


Which amp?



Another great design collaboration between Billm Audio and David Allen of Allen Amplification! the TO20B has the same dimensions and weight as the TO20, but is bifilar-wound for even better low-frequency response and efficiency. Choose the TO20B for a thoroughly modern, hi-fi design; choose the TO20 for a more vintage-style, layered-winding design. $69


TO26 Output Transformer for 6L6 Conversion

The TO26 is designed for maximum power from the cream board octal conversion mod, along with the TP24 power transformer. It is designed for 5881/6L6 operation. Do not order this transformer for octal/6V6 conversion. It comes with the leads trimmed to length, push-on connectors installed, and an aux speaker jack that automatically switches to 4 ohms when you plug in the second speaker.  The jack is partially prewired, with push-ons attached. Requires drilling a #38 hole for the mounting screw and a 3/8 inch hole for the aux jack. $69.


TP24 Power Transformer

Billm Audio’s ongoing collaboration with David Allen of Allen Amplification pays off again–a real upgrade power transformer! The new TP24 power transformer fits exactly and provides up to 30 watts of effortless power with the octal conversion kit and 6L6s. See the TP24 page for more details. Cream board only, US 120V only. $80.


Bias Board for TP24/Octal Conversion




The bias board provides the higher bias voltage necessary to control the higher plate voltage from the TP24 power transformer. It is required if you use the TP24 with 6V6, 5881, or 6L6 output tubes. It is not required if you use the TP24 with EL84s. No drilling required; fits in existing resistor holes. Cream board only. See the bias board page. $17.


Re-cap Kit – Blues Junior

Recap kit version

Electrolytic caps don’t last forever. They may leak, or the internal resistance (ESR) goes up over time. The result is mushy tone, oscillation, “tails” on notes and general lack of punch. See herefor what leaks look like. Since the basic kit comes with a single 100uF cap, all you need to finish the job is three 22uF caps. If, for some reason, you need to recap the entire board, you can also order the kit with one 100uF cap and three 22uF caps. You do not need the 100uF cap version if you have ordered the basic kit. Two 100uF caps will not fit on the board.


New! Standby Switch

By popular demand! This kit replaces your power switch with a heavy-duty Carling progressive switch. It has three positions: off, standby, on. The kit is plug-and-play; no soldering or cutting of wires.  See the Standby Switch for Blues Junior page. $20.


Aux speaker jack kit: $10

High-quality, all metal Switchcraft jack, pre-soldered leads, lock washer, and nut. Requires drilling a 3/8 inch hole adjacent to the existing jacks. The aux jack is in parallel with the main speaker jack and is intended for use with a second 8 ohm speaker or cabinet. It does not cut off the internal speaker. If ordered at the same time as the line out jack, below, they’ll be prewired together. An aux jack is included with the TO22 or TO26 output transformer.


Line out jack kit: $10

The line out jack takes the signal from the speaker and reduces it to line level so it can be run into a PA, mixer, or recording equipment. It preserves the tone of the output stage, but does not attempt speaker emulation. The line out jack does not cut off the speaker, nor is it intended for use with headphones. Tube amps require a speaker-like load all the time; a dummy load is required to run silent. Switchcraft jack, high-quality metal film resistors, pre-soldered leads.


Newest Mod: Octal socket conversion kit: $25




With octal output tube sockets, you can run 6V6s or, with the TP24, bias board, and TO26, 6L6s. I strongly recommend the JJ 6V6-S, a heavy-duty output tube that sounds more like a 5881 or 6L6, without the high filament current. Output power is up around 20 watts and the amp takes on a wonderful roundness with a brighter, glassier top end than you can get with EL84s. If you want to run 5881s or 6L6s, you’ll need the TP24, bias board, and TO26 output transformer. In either case, they give your Blues Junior an authoritative sound that you won’t believe. I also recommend that you do the cathode follower mod. The octal conversion is the most difficult kit: you have to accurately cut the fiberglass tube board, drill #38 holes in the chassis, make #30 and #34 holes in the chassis and tube board. FOR THE CREAM BOARD ONLY! See http://billmaudio.com/wp/?page_id=353

 


Excelsior Tone Control: $22




This mod for the Fender Excelsior replaces the bright/dark switch with a full-range tone control and pull-up switch, not just a pot to give you in-between adjustments between bright and dark settings. It attaches with just two solder connections and does not require removing any components from the circuit board. You do, however, have to file the switch slot slightly to mount the control. Supplied with vintage-style Fender brown knob. Pulling up on the knob gives you the Excelsior’s raw tone. See http://billmaudio.com/wp/?page_id=1506

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