Marshall Amplification JTM45 User Manual

From the Chairman

Congratulations on your purchase of the limited edition reissue of the offset JTM45 halfstack. The original versions of this amp and cabinet were built back in 1962, the very year in which Marshall Amplification was born. In fact, the offset head was the first version of the JTM45 my company made and only a mere handful of these heads and cabinets were ever constructed. In case you are wondering, the reason the amp's chassis was offset like this was to help ensure that the head balanced properly when carried. Despite the practicality of this design however, we quickly discovered that most people preferred the symmetrical look of a centrally placed chassis, so that’s how we’ve been building heads ever since!

A few years ago one of these extremely rare offset halfstacks came back into my possession and I immediately placed it in the Marshall Museum at our headquarters in Milton Keynes, England. Since then, all who have seen and heard it have commented most favourably - not only on its unique looks but also on its rich, fierce, majestic tone.

To celebrate the dawn of a new century I wanted to offer something truly special - hence this reissue. To make this unique product as authentic as possible, we have sought out and reproduced all of the original components and methods of construction we used back in 1962. From the hand-wired tag-board circuit housed in an aluminium chassis, through to the original silver Celestion Alnico loudspeakers. We have even resurrected the original ‘coffin’ logo!

I sincerely hope that this eye-catching reissue of one of the first Marshall amplifiers ever made, will provide you with countless hours of playing pleasure. I'm sure it will. I'm also sure it will prove to be a quite a conversation piece too!

WARNING!

Please read the following list carefully.

A. ALWAYS use the correct power cord B. NEVER attempt to by-pass the fuses or fit ones of the incorrect value. C. NEVER attempt to replace fuses or valves with the amplifier connected to the mains. D. DO NOT attempt to remove the amplifier chassis, there are no user serviceable parts. E. ALWAYS have this equipment serviced or repaired by competent qualified personnel. F. NEVER use an amplifier in damp or wet conditions. G. DO NOT switch the amplifier on without the loudspeaker connected. H. ENSURE that any extension cabinets used are of the correct impedance. I. PLEASE read this instruction manual carefully before switching on. WARNING : This apparatus must be earthed! WARNING : Do not obstruct ventilation grille and always ensure free movement of air around the amplifier !

KEEP THESE INSTRUCTIONS

Introduction

As Jim has already stated, our goal, when building this limited edition, offset reissue, was simple. To make it as close to the original as humanly possible! To this end we have gone to great lengths to recreate every single aspect and specification of this visually and aurally striking item-from sourcing an exact replica of the original coffin logo (so called because it was first made for us by a coffin manufacturer!), to ensuring that the output and power transformers boast the same exact core lamination materials as they did back in 1962. Likewise, the amplifier circuit itself is handwired on a hand-built tagboard, the chassis is constructed from aluminium and the valve complement is 3 x ECC83s in the preamp, a GZ34 rectifier and a pair of KT66s in the power amp - just like the original.

We are delighted to report that many of our suppliers went to the same exacting lengths as we did when providing us with parts for this reissue, and none-more-so than Celestion. Thanks to their commitment to this project they successfully recreated the Alnico magnet, silver G12, model T0652 loudspeakers found in our museum piece-right the way down to matching the same exact colours and lettering fonts used on the original label!

As is the case with all our amplifiers, the best way for you to truly appreciate this remarkable reissue is to grab your favourite guitar, plug it in and play. Enjoy!

JTM45 O/S Front and Rear Panel Features

Front Panel Functions

The JTM45 O/S features four inputs, two per channel. The first channel is voiced for a high treble response with the second channel voiced for normal response. The first input of each channel has more gain than the second input of each channel and hence is louder. Though the first input of the first channel is the input that most guitarists use, don’t hesitate to experiment. Some guitar players prefer to mix the two channels by putting a patch lead between the second input of channel 1 and the first input of channel 2 and then plug their guitar into the first input of channel 1. Doing this allows you to mix the different tonal characters of each channel for greater flexibility.

See Diagram right.

Front Panel Functions

1. Power Switch

On / Off Switch for mains power to the amplifier.

2. Standby Switch

Controls H.T. or high voltage to the valves to allow them to attain correct working temperature before playing. To prolong the life of the valves it is always advisable to switch on the Mains Power Switch (item 1) about 2 minutes before switching on the Standby (item 2).

On switching off, the Standby should always be switched before the Power Switch.

The standby facility is particularly useful live between sets and before playing, as it allows you to keep the valves operating at a functional temperature but without any sound being produced.

3. Presence Control

Adds higher frequencies to the guitar tone, creating crispness and bite. Turning this up will make the sound more cutting and further forward.

4. Bass Control

Controls the amount of low frequencies or bottom end in your tone.

5. Middle Control

Dictates the middle register of the amplifier. Turning this up will make your guitar sound fatter. Conversely reducing the amount of middle in your tone will result in a sharper and thinner guitar sound for the classic ‘scooped’ tone.

6. Treble Control

Controls the high frequencies of the guitar tone, making your guitar sound brighter when increased.

7. Volume I

Controls the overall output level of channel 1. Note - this channel is voiced for a higher treble response than channel 2.

8. Volume II

Controls the overall output level of channel 2. Note - channel 2 is voiced for normal response.

9. Input Jack

Connects the guitar to channel 1.

10.Input Jack

Connects the guitar to channel 1. Note - this input has less gain than item 9.

11. Input Jack

Connects the guitar to channel 2.

12. Input Jack

Connects the guitar to channel 2. Note - this input has less gain than item 11.

Rear Panel Functions

1/2. Loudspeaker Jacks

With all valve amplifiers it is imperative that the amp is connected to a load whilst in operation and that the impedance selected on the amp matches the total impedance of the speaker cabinet(s) being used. For example, if the amp is running into a single 16 Ohm cab, the amp should accordingly be set to 16 Ohms. If running into two 16 Ohm cabs, the amp should be set to 8 Ohms. If running into two 8 Ohm cabs the amp should be set to 4 Ohms.

Note - The matching cabinet supplied with this amp is wired for 16 Ohms.

Failure to comply with these points will result in damage to the amplifier.

3. Output Selector

Matches amplifier output transformer impedance to loudspeaker load impedance.

4. H.T. Fuse

See label for correct value.

5. Mains Input

Connects unit to power supply.

6. Mains fuse

See label for correct value.

JTM45 O/S Front and Rear Panel Features (continued)

JTM45 O/S Front Panel

10871 2

6543

JTM45 O/S Rear Panel

Whilst the information contained herein is correct at the time of publication; due to our constant improvement and development, Marshall

Amplification plc reserve the right to alter specifications without prior notice.

Marshall Amplification plc

Denbigh Road, Bletchley,

Milton Keynes, MK1 1DQ

England

Tel: (01908) 375411

Fax: (01908) 376118