Vox AC30: Burndept-made Top Boost chassis
Mid 1964 - 1968
Typical blue/grey panel on a Burndept-made chassis with integrated Top Boost controls. Left to right: VIBRATO: Speed and Vib/Trem switch / VOLUMES: Vib-Trem, Normal, Brilliant / TONE: Treble and Bass (the "Top Boost" controls), and Cut (the "old" tone control).
Chassis with integrated Top Boost controls. As is well known, the earliest chassis had copper panels and were made in the first instance by Westrex alone in late (very late) 1963 / 1964 principally for JMI's new "Expanded Frequency" AC30s. Such chassis were regularly marked on their undersides with an "X" in pencil. See this page.
Burndept began producing chassis with integrated Top Boost controls some months after Westrex and its chassis almost - note the qualification - always have grey/blue panels. There is at least one exception however:
Burndept, chassis no. 04565
Thanks to David for the pictures. "T/B Boost" stands for "Treble / Bass Boost" as does the flash of green paint. A page on Burndept colour codes can be found here.
It seems possible that the panel illustrated above was part of a small batch supplied to Burndept in March 1964 or thereabouts with a view to getting its run of Top Boost chassis moving while new grey panels were being made up.
The rule of thumb for Top Boost chassis (borne out time and time again) is not changed however: Westrex = copper; Burndept = grey.
The only other counter instances that have come to light so far are a small group of Westrex-made AC30 Super Twins from late 1964 / early 1965 with grey panels (and dome voltage selectors).
In terms of sales, the earliest Burndept-made Top Boost chassis currently known in an AC30 Twin is serial number 12019T (chassis number 4690), which has Mullard mustard capacitors with "I4N" date codes = first quarter of 1964 for their manufacture.
AC30 Twin serial number 11657 B - note the designation of Bass voicing - is now something of a patchwork. The Top Boost chassis (chassis number 04616) is fine, but the panel comes from an amp with a serial number in the low 21000s or higher. The knobs have all been replaced too.
AC30 Twin serial number 11657, chassis 04616.
Below, a provisional overview of early Burndept-made Top Boost chassis, different by nature from the standard chassis used for Normal, Treble, and Bass amps: preamp sections drilled for eight potentiometers instead of six; input jacks grouped more tightly, and so on. Wiring up is likely to have been undertaken on a separate bench or benches.
It is important to state that chassis were not selected for assembly (wiring up) in any strict order.
03916 - a reference only to this chassis being a Top Boost, perhaps incorrect. No further details at present.
04476 - Grey panel (?), AC30 Super Twin, serial number 2901TB. Certainly a Burndept-made Top Boost chassis, but much altered, and sold by a dealer known for swapping chassis and boxes around.
04530 - Grey panel, AC30 Twin, serial number unknown.
04551 - Grey panel, AC30 Twin, serial number 12411T.
04555 - Grey panel, AC30 Twin, serial number unknown.
04565 - Copper panel (original), AC30 Twin, serial number unknown.
04590 - Copper panel (repro?), AC30 Twin, serial number unknown.
04616 - Originally a grey panel (?), AC30 Twin serial number 11657B - chassis probably from another amp.
04690 - Grey panel, AC30 Twin serial number 12019T. Chassis (now with reproduction copper panel) forms part of a concocted Expanded Frequency AC30.
04916 - Grey panel, AC30 Twin serial number unknown.
05135 - Grey panel, AC30 Twin serial number 13098T.
05136 - Grey panel, AC30 Twin serial number 13763TB.
05214 - Grey panel, AC30 Super Twin serial number 2739T.