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Marshall JTM45 MK I

Schematic/Layout:

• jtm45_first.pdf

Model/Circuit Number: MK I (Tweed Bassman 5F6-A Clone)
Years of Production: 1962
Era: Offset Chassis
Configuration: Head and Ext. Cabinet
Controls: Polished Aluminum w/ Black Lettering
Knobs:
Faceplate

• Front: Polarity Switch, Power Switch, Standby Switch, Indicator Light, Presence, Middle, Bass, Treble, Volume 1, Volume 2, Channel 1, Inputs 1 & 2
• Rear: Speaker output 1, Bulgin Power Inlet, Fuse Holder

Cabinet

• Dimensions: 9'' x 26'' x 8 1/4''
• Hardware: None
• Handle: Leather Strap Handle w/ Gold End Caps
• Feet: Small Rubber Feet
• Corners: None

Covering Material

• Tolex/Tweed: Smooth Black w/ Brass Piping
• Grill Cloth: Marshall White Grill Cloth

Logo: Rectangular Metal Logo w/ Red Block Lettering
Weight:
Speaker

• Size: 12''
• Impedance: 15 ohms (Wired in series/parallel to a total load of 15 ohms)
• Model: Celestion G12T.652 Alnico

Effects: None
~Watts: 45 watts
Tubes

• Pre amp: 3 x 12AX7
• Power: 2 x 5881 Power Triodes (Early Production); 2 x KT66 (Later Models)

Bias: Fixed
Rectifier: GZ34

Comments: The Fender Bassman used a 12AY7 as the input tube, but the JTM45 was fitted with a 12AX7/ECC83, which has higher gain. The mix resistors (mix both channels together after the first triode sections) were originally 270K ohm on the early models. Sometime late in 1966, these mix resistors were raised in value to 470K ohm.