From around chassis number 3000, Burndept indicated the "voicing" of the chassis it produced for JMI not only with a stamp in red, but a colour code. "TREBLE" had a red splash; "T/B BOOST" (integrated treble and bass controls on panel) had green; and "BASS" - produced in smaller numbers - had blue. "Normal" AC30s had neither stamp nor colour.

The splash of colour was presumably supplied - while the chassis was on the assembly benches - to indicate how the voicing should be stamped above it.

It should also be said that circuit boards were also given a spot of colour - again to assist the assemblers. Top Boost boards have their spot of green at left; bass boards and treble boards have their spots (red and blue) at right.

A page on Burndept chassis numbers can be found here.

Treble - red

Detail of serial number 11613T, chassis number 3083.

Serial number 17169T, inspection stamp still clear. Note how the chassis is raised up from the slider board on washers. This was also standard JMI practice for AC50s and AC100s. When amps were repaired these washers were generally not replaced.

Serial number in the 11000s, chassis number 3098. Red flash on the circuit board.

Top Boost - green

Serial number in the 12000s, chassis number 4530.

AC30 Super Reverb Twin, "T B" for Top Boost stamped on the left side of the preamp. At present this is the only known instance. Thanks to Rich for the picture.

Burndept-made Top Boost chassis, number 04565, green on the board at left and on the chassis at right. Thanks to David, who pointed out the presence of colours on the boards of Burndept-made amps.

Bass - blue

Serial number in the 18000s, chassis number 8407.

Serial number 12554, chassis number 04291.