Decked out in the same silver vinyl covering and chrome-plated control panel previously only found on the 1987 Silver Jubilee amps, the new Marshall JCM 25/50 2555X also features the same unique 100-watt circuit driven by four EL34 and three ECC83 tubes that gave the Silver Jubilee head its distinctive blend of classic plexi and high-gain JCM800-style tones. There’s also the same two-channel design, input gain control with pull rhythm clip mode, and pentode/triode switch for selecting 100- or 50-watt output. The treble, mid, bass, and presence EQ section is shared by both channels, and Lead Master and Output Master (with push/pull channel switch) knob complete the front-panel controls.
Marshall made a few minor changes and updates to comply with modern regulations, improve performance, and compensate for discontinued parts. These changes are mostly evident on the rear panel, which now features separate 16- (x1), 8- (x2), and 4-ohm (x2) speaker output jacks instead of a pair of speaker outputs and rotary impedance switch. The old voltage selector switch is also absent, and voltage is now fixed. The 1/4-inch footswitch jack, series effect loop send and return jacks, and frequency-compensated line level DI output are still present and accounted for. Improved switching circuitry and DC heaters reduce noise to a minimum, and high temperature, high voltage resistant black fiberglass wires provide enhanced protection from damage. External bias points have also been added on the chassis.