Recap Kits · Pro Jr. Recap Kit
Fender Pro Jr RE-Cap Kit
Thanks for purchasing the Fender Pro Jr. Complete Modification Kit. After these simple changes you amp should sound far better than it does now.
Optional Tools/Supplies:
- Silicone glue.
- 9/16” nut driver or socket wrench.
- 1/2” nut driver or socket wrench.
- Fine point Sharpie or similar permanent marker.
- Masking Tape
Skills required:
- Basic soldering skills .
- Basic knowledge of electronics.
- The Ability to follow instructions.
Parts
- 100uf/450v EL Cap 100uf (Not included in Supreme Kit.)
- 22uf/500v EL Cap 22uf × 2
- 10uf/35v EL Cap 10uf × 2
- 22uf/25v EL Cap 22uf
- 330 ohm Resistor 330(For draining the caps)
Tools
- Temperature Controlled Soldering Iron and Solder
- Solder Sucker and or de-soldering braid
- Multi-Meter Capable of reading 500V DC
- Phillips Screwdriver
- Pliers with insulated handle
- Wire Cutters
- Safety Goggles
- Alligator Leads
1
Step 1
- WARNING: Performing these modifications WILL void the warranty on your amplifier. Working on amps can be deadly if you do not take proper precautions. Follow these instructions very carefully. If you are at all unsure of your ability to perform these modifications STOP and take your amp to a professional to be modified. You can also send your amp to me for modification.
- No Warranty: This kit and the instructions included do not include any warranty of any kind. The modifications to your amplifier are at your own risk and you agree to completely hold harmless the seller of this kit against any and all claims. Tube amplifiers contain parts that operate at very high temperatures and deadly voltages. If you are not sure of your abilities to perform these modifications then do not perform them.
2
Prep the Amp
- Instructions: Follow these instructions to the letter.
- It’s a good idea to have all the parts and tools you will need laid out before starting in a well lit area.
- Unplug the Amp and put on your safety goggles.
3
Step 3
- Remove the chicken head control knobs and the washer holding the input jack with a 9/16” in nut driver or socket wrench.
4
Step 4
- Remove the 6 screws holding on the back panel and remove the panel. If the back panel does not come off easily you can loosen the two chassis screws on the side of the amp about a half turn each.
5
Step 5
- Drain the Filter Caps: The filter caps on your amp may be drained already but you must follow these steps to insure that any deadly voltage is removed from the amp before you begin work. Test the voltage across the filter caps. Set your multi meter to DC and measure the voltage across the positive and negative side of any of the filter caps. If the voltage reads higher than 10 volts, then you need to drain the caps.
6
Step 6
- Using the insulated pliers to 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 measure again. Keep repeating this step until the voltage reads below 10V. Pictured is a Blues Jr but the Filter caps on the Pro Jr look the same.
- CAUTION: Capacitors can recharge even when the amp is not plugged in!!! After the filter caps are drained take an alligator lead and clip one end to the positive lead of the filter cap and the other end to the chassis and leave it there until you are done with your work. This will prevent the filter caps from re-charging.
7
Step 7
- Clip all of the wire ties. When putting the amp back together we will be re-routing most of the wires.
8
Step 8
- Unplug all the power and output transformer leads by pulling firmly with steady pressure gently rocking the lead terminal from side to side. 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 just mark the terminal number on the lead.
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Step 9
- Remove all the screws holding the circuit board.
10
Expose the circuit board
- 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.
11
Step 11
- 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.
12
Step 12
- 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. DO NOT PUT PRESSURE ON ANY COMPONENTS INCLUDING THE FILTER CAPS WHEN MOVING THE BOARD.
13
Removing the Old Components
- Be careful that your soldering iron is not too hot. The solder pads on the PCB are prone to curling and separating from the PCB, so remove the components with care, never using force. It is best to clip the component leads on the front of the PCB then remove the remainder of the lead and solder from the back side carefully with a solder sucker and de-soldering braid.
- This is an example of a pad that has come off the board during de-soldering. The trace next to the pad is carefully scraped to expose the copper and the lead will be bent and soldered to the trace.
14
Step 14
- Type Position Value Code
- EL Cap C15 100uf/450v 100uf
- EL Cap C17 and C18 22uf/500v 22uf
- EL Cap C13 and C14 10uf/35v 10uf
- EL Cap C23* 22uf/25v 22uf
- * Older Pro Jr. models have no C23.
- If your Pro Jr. has no C23 simply skip that capacitor.
- +
- -
- > Arrow points to Negative lead >
15
Step 15
- Above is the chart for all the caps and where they go with position numbers. Below is the board layout. 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.
- Note: Some older Pro Jr’s have two caps at C15 and C16 which are 22uf each. If this is the case with your amp, replace C15 with one 100uf cap and leave C16 empty.
- The circuit board will have a “+” sign closest to the hole where the positive 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.
- CAUTION: The circuit board is very fragile and the solder pads can easily become separated from the circuit board if extreme care is not used. Carefully examine each solder pad after removing the component to make sure the solder pad is intact. If the solder pad is damaged you will need to carefully scrape away the solder mask of the trace next to the hole, bend the lead to the trace and solder directly to the trace. Remember to always check continuity with your multimeter to insure that you have a good connection between components.
16
Putting the amp Back Together
- Carefully put the PCB back into place making sure that the pots and input jack all line up with the control panel.
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Step 17
- Replace all of the PCB mounting screws.
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Step 18
- Re-install all the transformer leads making sure that all the leads are put back in exactly the same place you took them from, which should not be a problem because you clearly marked where they all went with masking tape and a Sharpie.
19
Step 19
- Make sure all the ribbon cables have a smooth path with no kinks or sharp turns in the cable.
20
Step 20
- Dress the Transformer leads!!! The poor lead dress is a large part of the noise in this amp. Instead of using a new cable tie to put the wires back like we found them we are going to use standard wiring techniques for proper tube amp design.
- Twist the green heater wires and position as shown. All other leads should cross each other at 90 degree angles to avoid noise, hum, and oscillation.
21
Step 21
- Plug the speaker back into the speaker jack.
22
Step 22
- Re-install the control knobs and install the washer and nut on the new input jack.
23
Step 23
- Replace the back panel and make sure to tighten the chassis screws if you loosened them.