For builders chasing the canonical "Van Halen Plexi" tonal target, the chassis-era matters in specific, documented ways. Per Dave Friedman and Dan Gower across Amp Panel #8 and #9:
Screen supply (1965 — late-1969 Super Lead): - 2× 32µF capacitors in series = 16µF effective on the screen supply. - Per Friedman ([Panel #9 71:37]): *"the late 60s stuff was two 32s in series. Yeah. Like 16 total. On the Van Halen plexi kind of thing."* - Later in 1969, Marshall changed this; the late-69 and onward chassis use a different (typically larger) screen-supply value.
B+ rail ceiling on lay-down-transformer Plexi (1968–69 era): - B+ ≤ 470V max for the canonical tone. - Per Friedman ([Panel #9 73:36]): *"lay down transformer plexis almost always maybe 470 max [B+]. You need slightly saggier on the B+. That's a critical thing for that tone. Also like if you're talking about the EVH plexi, you have to have that voltage to get that sound just right."*
Reissue gotcha — 93 Super Lead 220pF treble-wiper-to-ground: - Marshall's 1993 1959 reissue includes a 220pF cap from the treble pot wiper to ground that originals do not have. - Per Dan Gower ([Panel #8 74:16]): the cap was added because Marshall *borrowed Warren DeMartini's actual Plexi as a reference for the reissue voicing* and his amp had this cap (possibly added later, possibly a service modification). The reissue cloned it as if it were canonical. - Gower's standard practice on the 93 reissue: *"I always just take it out. Compressed the hell out of the circuit."*
Power-tube and speaker context: - EVH-era tone depends critically on driving the speakers into saturation (Friedman, Panel #5 ~[30:41]). A loadbox-attenuated chain produces the preamp character but loses *"all that saturated gooey goodness… the speakers absolutely crying for mercy."* - The speaker-as-final-gain-stage premise is why JMIL's chain models real cabinet IRs but the simulation has irreducible limits on reproducing a fully-cranked stack at studio volume.
Implication for JMIL: EVH-tone education must include the speaker-saturation context — front-end and preamp modeling alone, however accurate, cannot fully reproduce the recorded tone. The chain in JMIL targets the preamp/voicing side of the equation; the power-amp + speaker side requires either the real thing or a more sophisticated simulation than a browser-resident chain can offer.