1968 Marshall Super Lead 100 Watt (Plexi, 1959)
The 1968 Marshall Super Lead 100 Watt (model number 1959, known universally as the "Plexi" for its transparent Plexiglas front panel) is the amplifier that defined rock and roll's sonic character for half a century. Hendrix, Clapton, Page, Townshend, and Slash all ran through Plexis. Understanding what makes a 1968 example specifically valuable requires understanding both the model's history and why this particular year sits at the apex of the collector market.
Jim Marshall and the Birth of British Rock Tone
Jim Marshall opened his drum shop in Hanwell, London in 1960 and began building amplifiers in 1962 at the urging of young guitarists who couldn't afford (or couldn't get) Fender amplifiers from America. Working with Ken Bran and Dudley Craven, Marshall reverse-engineered and modified the Fender Bassman circuit, substituting different capacitor values, adding a cascading gain stage, and using EL34 output tubes (rather than the American 6L6 tubes in the Bassman) to create a distinctly British character.
The original Marshall 100-watt amplifier, developed in 1965, was the first genuinely powerful stage amplifier purpose-built for rock guitar. The 100-watt head, paired with the 4x12 cabinet, created the "Marshall stack" configuration that became the visual and sonic symbol of rock amplification.
The Plexiglas Panel: Why It Matters to Collectors
From approximately 1965 to 1969, Marshall used a Plexiglas (transparent acrylic) panel on the amplifier's control surface. From 1969 onward, the panel changed to aluminum. "Plexi" Marshall amplifiers are specifically those made with the Plexiglas panel, and this period encompasses what most collectors and players consider the finest-sounding Marshall amplifiers ever made.
The circuits changed repeatedly throughout the Plexi period:
| Year Range | Notable Circuit Changes |
|---|---|
| 1965-1967 | Early JTM45-derived circuits, various output transformers |
| 1967-1968 | Transition to JMP, specific capacitor and resistor values |
| 1968 | The considered "sweet spot" by many collectors and technicians |
| 1969 | Transition to metal panel, circuit modifications |
The 1968 specifically is prized because it represents the fully developed Plexi circuit before the modifications that came with the metal-panel era. The specific component values in 1968 production, combined with the EL34 output tubes and transformer characteristics, produce the dynamic, touch-sensitive response that players describe as the most organic and musically satisfying Marshall configuration.
What Creates the Plexi Sound
The Plexi's character comes from several interacting factors:
EL34 output tubes: British-made EL34 tubes have a specific harmonic structure that contributes to the violin-like singing quality associated with the Plexi. The compression behavior as EL34s approach saturation is different from 6L6 tubes and central to the sound.
Output transformer: Marshall's original Dagnall transformers have specific saturation and frequency response characteristics. A Plexi with its original transformer versus a replacement has a noticeably different sound.
Input circuit: The cascading gain stages in the input section create the characteristic crunch and bloom when the amplifier is driven into saturation.
Voltage sensitivity: Original Plexis were designed for British 240V power. Running them at 120V (as required in North America without a step-up transformer) changes their operating point in ways that affect tone. Properly powered examples sound different from incorrectly configured ones.
Condition and Values
| Condition | Approximate Value |
|---|---|
| Excellent original, all correct | $25,000 to $60,000 |
| Very good, minor component changes | $15,000 to $30,000 |
| Player-grade, working, some mods | $8,000 to $18,000 |
| Heavy modification, original chassis | $4,000 to $8,000 |
These values apply specifically to genuinely dated 1968 Super Lead 100 Watt examples with verifiable dating. Amplifiers presented as 1968 without documentation require expert examination.
Dating a 1968 Marshall
Authentically dating a Plexi Marshall requires examining:
Serial number: Marshall maintained serial number records. The serial number should be consistent with 1968 production (approximately 3000-8000 range for this era, though ranges varied by model).
Tube chart: Inside the cabinet, a tube complement diagram was typically affixed. The printing style, typeface, and specific layout are period-specific.
Component date codes: Resistors and capacitors were often date-stamped by their manufacturers. All components should be consistent with 1968 or earlier production.
Transformer markings: Dagnall transformer date codes are the most reliable single dating element. The transformer should show 1968 production.
Chassis markings: Hand-stamped or stenciled chassis markings for model designation and serial number should be consistent with period production.
Provenance and Famous-Owner Premiums
Some Plexi Marshalls carry documented provenance linking them to famous players. A 1968 Marshall with documented connection to a major artist commands substantial premiums over an anonymous example. Such documentation must be supported by receipts, photographs, or other verifiable evidence rather than oral history alone.
Playing a Vintage Plexi
A properly serviced 1968 Super Lead through a period-appropriate 4x12 cabinet is an extraordinary musical experience. The dynamic range, the way the amplifier responds to picking intensity, the harmonic content of notes as they sustain and decay: these qualities justify the collector market's valuation.
Proper service before use is essential: filter capacitors must be reformed or replaced, bias must be set, and all tubes should be tested. A qualified vintage amp technician familiar with Marshall circuits is essential.
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