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WARNING Performing these modifications WILL void the warranty on your amp. Working on amps can be DEADLY if you do not take proper precautions.
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Follow these instructions very carefully. If at any point in the mod process you are at all unsure of your ability to do these mods take your amp to a professional to be modded. You can also send your amp to me to be modded.
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No Warranty - This kit and the instructions do not include a warranty of any kind. The modifications to your amplifier are at your own risk and you agree to hold harmless the seller of this kit against any and all claims
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Tube amps contain parts that operate at very high temperatures and deadly voltages.
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Unplug the amp and place on a level surface
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Remove the chicken head control knobs by loosening the set screws( if your control knobs have those). Remove the nut and washer holding the input jack on the top panel
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Remove the screws holding on the back panel and remove the panel. If the back panel does not come off easily you can loosen the chassis screws on the side of the amp about a half turn each
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The filter caps on your amp may be drained already but you must follow these steps to ensure that any deadly voltage is removed from the amp before you begin work.
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Test the voltage across the filter caps. Set your multimeter to DC and measure the voltage across the positive and negative sides of any of the filter caps. If the voltage reads higher than 10 VDC, then you need to drain the caps.
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Using insulated pliers, hold the power resistor touch one lead of the resistor to the negative side of the filter cap and the other to the positive side, leave the leads in contact with the power resistor for 30 seconds, and test the voltage again. Keep repeating this until the voltage reads below 10V.
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Clip all of the wire ties
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Unplug all the transformer leads by pulling firmly with steady pressure gently rocking the lead terminal from side to side
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As you remove each lead mark the wire with masking tape and a Sharpie so you will know where to plug it back in when you are putting the amp back together. I write the terminal number on the lead
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Remove the pilot LED from the top of the chassis. It should just unsnap when pulled while squeezing the white LED holder
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Remove all of the screws holding the tube pcb board
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DIsconnect footswitch and speaker jack assembly from the chassis
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Gently, with putting as little strain and lateral motion on the ribbon cable, lift the tube board and footswitch/ speaker jack assembly up and free of the chassis
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Remove all screws holding the PCB to the chassis and remove the grounding lug screw.
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Pull gently on the board to make sure that it is not stuck to any of the standoffs that were holding the circuit board screws.
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Press the wires from the output transformer as far away from the board and as close to the chassis as possible. The board needs to come down toward the bottom of the amp before the pots will clear the top of the chassis as shown.
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Using gentle pressure on the top of the circuit board press the board down making sure it is not getting hung up on any wires until the pots have cleared the top of the chassis then pull the board to you to expose the underside.
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DO NOT PUT PRESSURE ON ANY COMPONENTS INCLUDING THE FILTER CAPS WHEN MOVING THE BOARD.
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The solder pads on the PCB are prone to curling and separating from the PCB, remove the components with care, never using force. We recommend using de-soldering braid as solder suckers can rip the pads off the PCB
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For axial components (leads on each side), it is best to clip the leads on the front of the PCB then remove the remainder of the lead and solder from the backside carefully with de-soldering braid. For radial components (both leads on bottom) it is best to remove the solder first
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The ribbon can can be fragile so it's best to move it as little as possible
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Remove C11, C13, and C25
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Install 270p at C25, .1 at C11, and .015 at C13
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At R29 which is the Mid Tone Pot, bridge pins 2 and 3 which are the hole closest to the master volume pot and the center hole. Use any clipped lead for this function. You can also bridge the pins on the solder side of the board
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After these mods your amp will not make sound with all of the tone controls all the way down. This is on purpose! What you're doing is changing the tone stack to a vintage style which gives you a greater range on the mid pot.
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If your kit came with open frame jacks follow the instructions below
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Remove input jack. This part is snapped into the PCB and then soldered. I find it's easiest to remove the solder from the back side first and then remove the jack
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Solder the wires included in the kit to the jack as shown. The ground wire should bridge the ground and middle( switch) lugs
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Install the jack on the PCB with the ground/ switch connection closest to the top of the board and the tip wire closest to the bottom
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If your kit came with the Fromel input jack PCB follow the instructions below
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Remove input jack. This part is snapped into the PCB and then soldered. I find it's easiest to remove the solder from the back side first and then remove the jack.
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Solder the jack to the jack PCB oriented as shown in the photo
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Attach leads to the jack PCB at SIG and GND
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Connect the leads from the jack PCB to the Blues Jr main PCB at the points shown in the photo
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Remove C20, R40, and R56
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Install the prewired reverb mod which consists of C20(330p) with a lead to R40 (430K resistor) joined to R56 (470K resistor). Install the kit as shown with the lead to C20 installed in the right side of where the old component used to be,
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the other leg of C20 will have a lead to the right side of R40 and the leg of R56 on the left side. R40 gets replaced as it was before and the open leg of R56 goes in the top hole of where it used to be
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Make sure you mind the polarity of the caps, they must be inserted the right way or your amp will have problems which could be serious
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Remove C3 and C4 on the left side of the board near the first ribbon cable
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Install 22uf/ 50v in C3 and 2.2uf/ 50v in C4
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Remove C17, C18, and C10
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Install 22uf/ 500v in C17, C18, and C10
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The circuit board will have a “+” sign closest to the hole where the posi-tive lead of the cap goes. The axial caps have an indented ring on the positive side and a “-” sign in an arrow pointing to the negative side. For radial caps the longer lead is the positive side and there is a “-” sign in a band closest to the negative terminal
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The voltage rating on caps for C3 and C4 in the kits can be anywhere from 25V to 63V for this part depending on our supplier. This voltage rating is a maximum working voltage and for where they are used in the circuit they will see less than 10V.
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Carefully put the PCB back in place making sure that the pots, fat switch, and input jack all line up with the control panel and replace all the PCB mounting screws
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Put the tube PCB back in place making sure to not stress the ribbon cables while doing so and that there are no kinks or sharp turns in the ribbon cable
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Dress the transformer leads!! Poor lead dressing will contribute to the noise in an amp. Instead of replacing the cable ties we removed we're going to use standard wiring techniques for proper amp lead dress. Twist all AC pairs together: twist green wires together, red, and brown. All twisted pairs should cross each other at 90 degree angles
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Reinstall the the small board with the speaker and footswitch jacks, the lock washer goes on the inside between the chassis and the jack. Don't overtighten the nut or you'll strip the threads
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Reinstall the control knobs and install the nut and washer on the input jack. Replace the back panel and install the washer and nut on the new input jack
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ENJOY YOUR NEW AMP
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