1973 Marshall JMP Model 1987 50W Lead head, professionally modified by Swedish amp designer Tommy Folkesson with his Mk III modification, together with a vintage Marshall 4x12 cabinet loaded with four Celestion G12M 25W 16-ohm Greenbacks.

This is a highly unusual and extensively documented vintage Marshall rig that I have owned for many years.

Amplifier Head

The amplifier is a 1973 Marshall JMP Model 1987 50W Lead, identified by chassis serial/date code 6143E.

It was modified by Tommy Folkesson with his Mk III modification, which Tommy has personally confirmed was a modification he performed during approximately 2000–2004.

The Mk III provides four selectable sounds:

Clean / Crude / Crunch / Lead

The original Folkesson four-button footswitch is included.

The amplifier also features the extensive rear-panel Folkesson control section with individual Gain/Tone/Volume controls, effects send/return, an additional 12AT7 distortion stage and a Pentode/Triode output-stage switch.

According to Tommy Folkesson, the BITE control is a pre-shape filter active on the Crunch and Lead sounds. The first half of its range is intended primarily for single-coil pickups and the second half for humbuckers.

Professional Inspection – October 2026

The amplifier has just been professionally inspected and serviced by Ola Insulander Musik, Stockholm.

The inspection/service included:

• Original transformers and major components verified
• All tubes tested
• One weak ECC83 replaced
• Bias adjusted
• Folkesson 12AT7 tested healthy
• Impedance selector inspected/repaired and set correctly to 16 ohms
• Pentode/Triode modification checked
• Output measured at approximately 45W Pentode / 22W Triode
• Amplifier tested and found to measure and operate correctly

The original output transformer marking 784-139 is documented in the internal photographs.

The service invoice and detailed internal photographs are included as documentation with the amplifier.

Vintage Marshall 4x12 Cabinet

The cabinet is a vintage Marshall 4x12 marked:

Serial No. 43162
Stock No. 1935
100W

It is loaded with four matching-type Celestion G12M Greenback speakers, each rated at 25W / 16 ohms.

One clearly documented speaker carries chassis code:

T1511 / EC18

The EC18 Celestion date code corresponds to 18 May 1970.

The cabinet measures approximately 13.8 ohms DC, consistent with a nominal 16-ohm cabinet, and the amplifier is now correctly set for 16-ohm operation.

Included With the Sale

The sale includes:

• 1973 Marshall JMP Model 1987 50W Lead / Folkesson Mk III head
• Vintage Marshall 4x12 cabinet with four Celestion G12M Greenbacks
• Original Folkesson four-button Clean / Crude / Crunch / Lead footswitch
• Vintage Marshall protective cabinet cover
• Service documentation and internal photographs
• Detailed illustrated English user/reference guide – v5 FINAL

The vintage Marshall cover shows normal age-related wear and patina, as pictured.

The amplifier and cabinet naturally show cosmetic wear consistent with vintage equipment of this age. Please study the photographs carefully; I have deliberately documented the condition rather than attempting to hide or restore the patina.

A detailed illustrated English reference guide documenting this specific amplifier, its Tommy Folkesson Mk III modification, controls, cabinet, speakers and recent professional inspection is included with the sale. It brings together the technical details, photographs and documented history of the complete rig in one convenient reference.

Shipping

Located in the Stockholm area, Sweden.

Local pickup is welcome, but European/international shipping can also be arranged.

Due to the size and weight of the rig, the amplifier head and 4x12 cabinet will be packed separately and very carefully.

Please contact me before purchase for an exact shipping quote to your location.