Marshall

JMP 50 – 1974

Model 1987 Mk II Lead head with master-volume modification.

Serial number: S/A 6474F

Inspection date: 21 August 1974

A great-sounding, professionally serviced 1974 Marshall JMP 50 retaining its original Drake transformers and choke.

This is a player-grade vintage Marshall rather than an untouched collector’s example. It combines the desirable original iron and classic four-input Model 1987 circuit with a practical pre-phase-inverter master volume, making it considerably easier to use in the studio, at rehearsals and on stage.

Most importantly, the amp has recently been thoroughly serviced by Dave Wittering of Prestige Amp Servicing, a former senior Marshall service engineer. It has been inspected, correctly biased, PAT tested and is in full working order—ready to be played rather than requiring the recommissioning often associated with an amplifier of this age.

ORIGINAL TRANSFORMERS

• Original Drake 1202-164 mains transformer
• Original Drake 784-139 output transformer
• Original Drake choke

MASTER-VOLUME MODIFICATION

A pre-phase-inverter master volume has been installed in the position originally occupied by the power indicator. The indicator has been repositioned alongside it. The modification has been inspected and tested during the recent service and operates correctly.

The modification is clearly shown in the photographs. It provides useful control over the amplifier’s overall output while retaining the character and response of the original JMP preamp.

RECENT SERVICE WORK

The work carried out includes:
• V1 and phase-inverter anode resistors replaced as required
• Phase-inverter anode load resistor replaced
• Bias reservoir and smoothing capacitors replaced
• Screen resistors replaced
• Control pots replaced
• Speaker output sockets replaced
• Marshall-branded ECC83S preamp valves fitted
• Bias set to the correct specification
• Protective chassis earth fitted
• PAT tested

VALVES

Preamp: Marshall-branded ECC83S valves
Power amp: matched Marshall-branded EL34 valves

CONDITION

The original head shell, black covering, feet and cosmetic hardware remain in place.

Cosmetically, the amplifier presents very well for a working vintage head of more than five decades. There are various small marks, snags and areas of wear to the covering, with most of the more noticeable wear located on the underside. Please study the detailed photographs, which form part of the description.

The replaced electronic components and master-volume modification are fully disclosed. This is an excellent choice for a player or studio looking for the sound and feel of an original 1974 JMP 50 without paying the premium—or accepting the uncertainty—associated with a completely untouched example.

VOLTAGE AND SHIPPING

The mains selector provides 110V, 120V and 240V operation, making the amplifier suitable for use in the UK, Europe, North America and other compatible regions when correctly configured.

Collection is welcomed at our Hayes showroom.

Worldwide shipping is available.

The amplifier will be packed in a custom-made Overdrive Guitars shipping carton with substantial internal protection. We regularly ship vintage Marshall amplifiers throughout the UK, Europe and North America, normally using UPS for international orders.

Overdrive Guitars is an authorised Marshall retailer and an experienced seller of vintage Marshall amplification. Please contact us with any questions, to arrange an audition or to obtain an international shipping quotation.