Marshall Amplification
Marshall Amplification is a British manufacturer of guitar amplifiers, speaker cabinets and effects pedals, founded in London in 1962 by shop owner and drummer Jim Marshall (his Hanwell drum shop launched the business); based in Bletchley, Milton Keynes, its Bluesbreaker/JTM-era amps of 1962–65 and the JCM800 series (1981) became the archetypes of British rock loudness.^[raw/articles/wikipedia-marshall-amplification.md]
Why it matters to the Hammond story
Marshall matters here in a paradoxical way: the most famous distorted Hammond sound of all time is a Hammond organ plugged into Marshall amplifiers. Jon Lord drove his Hammond B-3/C-3's Leslie output into overdriven Marshall stacks, deliberately distorting the organ to match Ritchie Blackmore's guitar attack — a "growling, heavy, mechanical" tone that let the tonewheel organ stand as a full rock lead voice.^[raw/articles/wikipedia-jon-lord.md]
That rig decision, more than any circuit design, defined hard rock's organ sound (see Landmark Hammond albums for what it produced on Machine Head). Marshall is not an organ maker — but in the Hammond rock canon it is the amplification that made the organ heavy.