Vintage Tag

23 Sep The Evolution of the 100W Circuit: From JTMs to JMP Superleads

From Fil ‘SoloDallas’, just an introductory word for our friend Roe. Roe has been on the hunt for AC/DC’s tone at least since I have been; that means, years and years, if not decades. So it’s not something it started yesterday. It’s been a long way coming. Roe’s original link (added) denotes him being a researcher (like us) and collector of various information, scattered around places and time. He has been an inspiration for us at SoloDallas as well as a source of primary information. It would not be fair reproducing his work here without these lines of mine. May information be divulged honestly and properly for the sake of us all, always.

Love, Fil

Reproduced from: The Evolution of the 100W Circuit: From JTMs to JMP Superleads

By Roe Fremstedal ©2011-2012

This article tries to give an overview over the early Marshall 100 watt amplifiers by piecing together available information and shedding new light on transitional models from 1967. The first 100 watt amps – known today as “JTM45/100s” – used “JTM45” plexi faceplates and white “Super 100 Amplifier” back-plates. However, the 100 watt PA amps used “JTM100” faceplates. In 1967 several changes were made. First, the plexi “Superlead” and “Superbass” backplates were introduced, then the so-called “Black Flag” “J.T.M.” plexi faceplate was used in a transitional period. Finally, the “JMP” plexi faceplate replaced the earlier faceplates. The main stages in the evolution of these early 100 watt amps are:
1. Prototypes (1965)
2. Amps with dual output transformers (1965)
3. First amps with single output transformer (1966)
4. First EL34 amps (1967)
5. Second series of EL34 amps with dual rectifiers (1967)
6. JMP faceplate and new power supply (1967)
7. New Superlead circuit (1968)
8. New chassis and higher filtering (1969)
9. Yet another chassis, last plexis (1969)
10. Aluminium panel amps (1969-) (more…)

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