Mod Kits and Services
All the kits you need for a great-sounding Blues Junior, selected for quality and performance. The cart buttons automatically calculate domestic mailing, but I will fill international orders too. Please use the button at the bottom of the page to select proper international postage. US shipments go Priority Mail, international shipments are First Class International (no tracking).
I have a considerable backlog of orders to work through. It may take two weeks or more for me to fill your order, but be assured that it will get filled.
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 #55 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.
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 pair of power supply stiffening capacitors, even a #55 high speed steel drill for a professional job installing the adjustable bias and power supply stiffening cap. The adjustable bias is a high-rel, precision, sealed, 25-turn trimpot for setting your bias accurately. The power supply stiffening capacitors double 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. With the green board kit, you get two caps so they fit properly on the board. 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.
Too easy to be a kit: the TwinStack mod greatly improves tone stack flexibility. This has been getting rave reviews on the Fender Discussion Pages: The TwinStack Page. I recommend that you do this as part of the basic mods, as I do when I mod Blues Juniors. Just use a scrap of wire!
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.
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.
Switchcraft all-metal Input Jack: $10
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 control: $10
Hate the way the loudness jumps up between 1 and 2 on the master volume when you’re trying to play quietly? The audio taper control expands the 1-2 range to 6 or so, then things get much louder beyond that. Ideal for home/apartment playing; doesn’t affect maximum loudness. A solder sucker is recommended to remove old pot. The shaft is shorter than stock; aftermarket setscrew knobs may not work; we have an option for Texas Reds and other Blues Juniors that use aftermarket, screw-on knobs.
Audio-taper reverb control: $10
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. The shaft is shorter than stock; aftermarket setscrew knobs may not work; we have an option for Texas Reds and other Blues Juniors that use aftermarket, screw-on knobs.
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. 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 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 a heavy-duty 4/8 ohm switch, partially prewired, also with push-on. Requires drilling a #38 hole for the mounting screw and a 15/32″ hole for the impedance switch. Choose this transformer if you intend to run an auxiliary speaker or a 4 ohm load most of the time or all of the time. The basic mods are essential to get the best performance from this or any other upgrade output transformer. $65.
New! Low Profile TO20 Output Transformer
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 requires no drilling. The low-and-wide core design provides all the heft and performance of the 22-watt 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. The basic mods are essential to get the best performance from this or any other upgrade output transformer. $55.
Re-cap Kit – Blues Junior
Those Illinois caps have never been great. Even if they’re not physically leaking, they may have high internal resistance (ESR) or be below spec capacitance-wise. The result is mushy tone, oscillation, “tails” on notes and general lack of punch. The re-cap kit comes in three versions. All have three 22uF caps; the only difference is whether you get zero, one or two 47uF caps. For instance, if you order a cream board basic kit, you’re already getting a new 47uF cap, so you need one more, plus the 22s. If you ordered a green board kit, it comes with two 47s, so all you need are the three 22s. But if you need a whole set, for whatever reason, that’s an option too.
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.
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. 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. You can try 5881s at your own risk, but the amp will get pretty darn hot by the end of a gig. In either case, they give your Blues Junior an authoritative sound that you won’t believe. Requires either Heyboer output transformer — and basic mods, of course. I also recommend that you do the cathode follower mod. This is a more 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. JJ 6V6s available below. FOR THE CREAM BOARD ONLY! See http://billmaudio.com/wp/?page_id=353
US Priority Mail shipping for any combination of the non-transformer kits is $5.00. Either transformer raises postage to $10. US postage is calculated automatically.
International Shipping: There is one rate for Canada, another for everywhere else. All international shipping is via First Class International. Please choose your location and rate from the options below. If you require another shipping method, please email me at billmaudio@gmail.com before you order!