AC50 mark 3 - chassis and components

1965.

Below some details and measurements of the chassis of an AC50 mark 3 (III) - solid state rectified - from 1965, serial number in the high 3000s, assembled for JMI by Burndept Electronics - chassis number 00557.

Back to the main sequence of .

The first of a series of posts on the metalwork of the AC50 mark 3 chassis. Below, the plinth.

STEEL: 1/16" thick, passivated.

DIMENSIONS: 16 1/2" x 6 3/8".

OT cutout: 2 1/8" x 2 3/4".

OT corner holes, centre to centre (for 2BA screws): 2 1/2" x 3 1/8", diam. 3/16".

MAINS TR. cutout: 2 5/16" x 3 1/8".

MAINS TR., corner holes, centre to centre(for 2BA screws): 3" x 3 3/4", diam. 3/16".

VALVE BASE HOLES: 1 1/16" diam.

BIAS POT HOLES: 5/16" diam.

CAGE NUT HOLES: 3/8" x 3/8".

HOLES for smaller screws (4BA): 1/8 diam".

UNDERSIDE OF CENTRE TO FOOT: 1 1/8".

WIDTH OF CENTRE: 5 5/16", including width of metal, at the top; 5 3/16" at the bottom - the sides are angled in slightly.

SIDE FLANGES: 9/16".

The upright of the preamp attaches to the side of the plinth above. The holes are for wiring pass-through as well as screws.

WIRING HOLES: 3/4" diam., to accept rubber grommets on preamp upright

SMALLER PAIRED HOLES (for capacitor clamp screws): 5/16" diam.

AC50 mark 3 metalwork, part 2: the control panel.

Anodised aluminium with etched brass embossing. DIMENSIONS: 16 7/16" x 2 15/16".

INPUT JACK HOLES: 5/16" diam. HOLES FOR POTENTIOMETERS: 3/8" diam.

MAINS SWITCH HOLE: 1/2" diam. BULGIN LAMP: 3/8" diam. BELLING LEE fuseholder: 5/8" diam. with notch. VOLTAGE SELECTOR: 1 1/16" diam.

AC50 mark 3 metalwork, part 3: the aluminium preamp shell.

ALUMINIUM: 1/16" thick, anodised.

DIMENSIONS OF UPRIGHT: 16 1/2" wide, 5" high.

DEPTH OF TOP (for control panel): 2 7/8".

LIP: 9/16".

PREAMP VALVE HOLES: 3/4" diam.

SLOTS (for securing the aluminium to the transformer shrouds): 3/16" wide (for 2BA bolts).

PASS-THROUGH HOLES: 1/2" diam.

OTHER HOLES: 1/8" diam. (for 4BA).

CAGE NUT HOLES: 3/8" square.

To show the profile of the edge.

AC50 mark 3, part 4: the underchassis tagboard; internal fuseholder; voltage selector; and output terminal block. Tomorrow, the remaining fittings.

TAGBOARD: Radiospares, standard "group panel". Miniature "group panel" was used for the preamp.

VALVE BASES: Macmurdo, as in preamp.

POTENTIOMETERS: Egen Electric Ltd. See on the Vox AC100 website

RESISTORS: Erie 1/2W, type 8.

TERMINAL BLOCK (to speakers): Radiospares. Also referred to as "Barrier Strip".

VOLTAGE SELECTOR: specially made for Vox, manufacturer unknown.

INTERNAL FUSEHOLDER: Bulgin F27/3. Vox also used fuses supplied by Bulgin.

INDICATOR LAMP: Bulgin D180.

AC50 mark 3, part 5: input jacks; preamp fittings. Fuseholder, control knobs, and on/off switch still to come.

INPUT JACKS: Rendar Instruments Ltd.

TAGBOARD: Radiospares, miniature "group panel".

CAPACITOR CLAMPS: unknown.

RUBBER GROMMETS: marked P.B.C. G9, maker unknown.

RESISTORS: Erie 1/2W, type 8.

25uf CATHODE BYPASS CAPACITORS: Gold-coloured TCC (Telegraph Condenser Company) Micropack.

COUPLING AND TONE CAPACITORS: WIMA Durolit.

AC50 mark 3, part 6: fuseholder, control knobs, and on/off switch. Just to add that the company that did much electro-plating work for Jennings in the second half of the 1960s and perhaps before was "Holmes Plating" in Blackheath.

FUSEHOLDER and CONTROL KNOB: Belling Lee and Bulgin.

CONTROL KNOB: Detail of Bulgin name. Unmarked chickenhead knobs were also used, probably from Radiospares.

ON/OFF SWITCH: Arrow "black bat" - the one above is from a different amp though.

On to the preamp.

On to the power amp.