Pre-production JMI printed circuit boards

1966

Pre-production Defiant. From left to right: mixer board (standing transversely); reverb; treble channel; tremolo (to the right, above); normal channel. JMI and its contractor (Burndept) experimented with different positions and formats for these boards during the second half of 1966.

For other pre-production amps, see this page. Standard production Defiants, which are very different, can be found here.

Below, an overview of the character of the circuit boards (and potentiometers) in the pre-production Defiant (from later 1966) illustrated above.

NORMAL CHANNEL BOARD: as Thomas (June 1966 circuit diagrams), not as standard JMI production amplifiers (1967).

BRILLIANT CHANNEL BOARD: not as Thomas. Aligns with JMI production amps (though not identical). All known JMI pre-production amps have variable distortion though - including the Conqueror displayed in London in August 1966. When Thomas did come to work it in later (see yesterday's entry), it was invariable, either on or off.

TREMOLO BOARD: still to be examined, but likely to be much as Thomas. Allowing for a few differences here and there the Thomas circuit aligns with the one found in JMI production amps.

MIXER BOARD: entirely different from Thomas. The circuit is much the same as the one in JMI production amps.

REVERB BOARD: not as Thomas. Aligns with JMI production amps (though not identical).

These for the time being are the bare facts.