Master Jim Mk III Amplifier
The ValveTone Master Jim is an all-valve guitar amplifier with a clean power output of 30 watts into 4 or 8 ohms. Its preamp
voicing is reminiscent of 1980's era JCM800 amplifiers, although it is not a clone of these amps. Typical applications for the
Master Jim amplifier include live performance where onstage volume is moderate, home practice ( where playing loud is
permissible ), rehearsal and studio recording.
Master Jim amplifiers are hand-built, one at a time, using traditional point to point wiring techniques. Construction is on a
diecast aluminium box, which is fitted to a headshell covered in blue tolex. ( Other colours are available by special order. )
Front Panel Controls: There are two front panel inputs, the left input having considerably more gain than the right input.
The right input provides a clean platform for use with external effects pedals, while the left input is
better suited to direct connection of a guitar.
VOLUME & MASTER: These controls set the output level and overdrive. Turning volume down and
master up gives the maximum clean sound, while volume up and master
down produces overdrive and distortion.
BASS, MIDDLE, TREBLE: These controls alter the signal tone as their names indicate.
PRESENCE: This control can be used as an additional boost to mids and highs.
The Master Jim amplifier will drive any type of guitar speaker cabinet. There are back panel outputs for either a 4 or 8 ohm
load. A 16-ohm speaker cab can be used safely on the 8-ohm output, but the available power will drop to about 25 watts.
Output valves supplied with the amplifier are new Shuguang EL34-B, but any new or NOS (new old stock ) EL34 or 6CA7
valves can be used as replacements. When replacing the output valves, the bias must be reset. The recommended bias is
45 to 55 milliamps per valve. Bias measuring points are provided inside the amplifier chassis.
The two preamplifier valves are located closest to the input socket, and are selected for minimum noise and microphonics.
New 12AX7 valves have been supplied, but any valve in the 12A*7 family ( 12AT7, 12AU7, 12AY7, 5751 ) can be used -
changing the valve type will alter the gain and may also change the tone. The phase splitter valve is also a 12AX7 but it is
recommended that it not be changed to a different valve type - no harm will be done, but the amplifier may have reduced
output until the correct valve type is back in place.
There is a complete build description of a Master Jim amplifier at the "Australian Guitar Gear Heads" forum:
Master Jim amplifiers are on display and usually available for immediate purchase at:
River Music, Windsor www.rivermusic.com.au
Tym Guitars, Brisbane www.tymguitars.com.au
Music Swop Shop, Melbourne www.musicswopshop.com.au
Intending purchasers who are unable to visit one of the resellers listed above, can buy directly from ValveTone Amplification.
The Master Jim Mk III amplifier is $945AUD including pack & post to any Australian address. Master Jim amplifiers are
hand-built, one at a time, so lead time for delivery is about two weeks. Payment is by direct deposit into our bank account.
The Master Jim Mk III amplifier has a twelve-month return-to-base warranty on both parts and labor - excluding valves - which
have a one month warranty.
If you require any additional information regarding the Master Jim Mk III, or any other ValveTone amplifier, please contact us
via the email address at the bottom of this website's home page.
Return to Homepage