Plexi Mods - Marshall Amp Modding Secrets!

JTM 45/100 ‘Hendrix Mod’

Supposedly a modification Jimi Hendrix used to carry out on all his Marshall 100w amps was to change the tone stack to a 33k/500pf resistor and capacitor combination, provided the amp didn’t already have this tone stack. This rumour was verified when the owner of the JTM 45/100 used extensively by Jimi Hendrix was given to Marshall by a Mr. Dickinson who bought the amp after Jimi’s death, and it was found to contain this sole modification.

Assuming your JTM 45/100 or similar early 100w Marshall amp has the 56k/250pf tone stack combination, first you need to locate this on the circuit board. It should look something like this:


or this:

12000 series tonestack

I’ve circled the two components in black. They should be a 56k resistor (bottom circle) and a 250pf capacitor (top circle). Change these out to a 33k resistor and 500pf capacitor respectively.

If you want to be able to switch between these two tone stacks, I’ve drawn up two diagrams in the general/other mods section that shows the different ways in which you can wire up a simple switch to change between them.

Text copyright © Richard Baines 2006

Related posts:

  1. Switchable Tone Stack
  2. Tone Stack Lift
  3. 2203/2204 Tonestack Mod
  4. V2a Cathode Switch
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1 Comment

  1. Hey, this looks like a cool website but looks like it was left dead for about 2 years.

    I have some questions about the Hendrix Mod. What voltage rating should the cap be for
    Method #2? Also, what wattage rating should the resistor be for Method #2?

    Hope to hear back….