How to Replace the Mesa Dual Rectifier Filter Caps
- 1). Turn off the amplifier.
- 2). Place the amp on a flat, elevated surface.
- 3). Unscrew the back panel with a Phillips screwdriver. On Dual Rectifier amplifiers the back is only partially enclosed. Depending on the model, you'll see either a metal bar or a wooden panel covering the back.
- 4). Loosen and remove the screws anchoring the preamp chassis to the cabinet. These are on the corners of the preamp chassis.
- 5). Slide the preamp chassis toward you and place it on your work bench. The wiring is long enough to permit you to remove the preamp chassis without disconnecting it from the speaker.
- 6). Unscrew the chassis lid and place it face-up. This exposes the preamp circuit board, upon which the filter capacitors are located. The tubes and transformers are mounted on the chassis lid, so be careful when removing it.
- 7
Set the voltmeter to "Resistance" to test the capacitor.Polka Dot Images/Polka Dot/Getty Images
Fit a voltmeter to the positive terminal on the base of the capacitor. Turn the meter on. The reading should be at least 15 volts, if not, the capacitor is most likely shorted. The filter capacitors are the tubular components wired into the circuit board. If you have a schematic, the filter capacitor is denoted by the letter "C" and a series of numbers, according to its capacitance value. This information is also silk-screened onto the circuit board, to further aid identification. - 8). Press the clean tip of a soldering iron against the solder joint fusing the filter capacitor to the circuit board. This melts the solder joint. The filter caps in the Dual Rectifier aren't board-mounted; they are wired to the board eyelet. This means you can remove them without removing the circuit board.
- 9). Discard the capacitor. Wipe away any solder residue from the tip of the wire.
- 10
Put a small amount of solder on the tip of the iron. Press the iron against the wire and the solder terminal on the base of the new capacitor to connect it to the board. Repeat the testing process for each capacitor. Repeat the removal and replacement process for each capacitor that tested faulty. - 11
Screw the lid back on the chassis, slide it back inside the amplifier cabinet and enclose the back.
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