A Vox AC30/6 chassis: early 1963

Below, notes on and pictures of an AC30 chassis assembled by Burndept in early 1963, serial number probably in the low 7000s. The cab along with speakers and serial number plate parted company in the 1980s.

Component date codes

Chassis number: 01518, stamped on the chassis by the output transfomer.

Woden transformers: date code "AU" = January 1963.

Potentiometers: date code "AK" = January 1963.

Hunts main filter cap (16+16uf): date code "YTI" = 4th week of 1963.

Hunts 250uf cap. (underchassis): "ISH" = 35th week of 1962.

Hunts 32uf cap. (underchassis): "YWI" = 1st week of 1963.

Welwyn wirewound resistors: "TL" and "TM" = December 1962.

Hunts preamp caps: "SWH" = 51st week of 1962.

Brimar GZ34 (Mullard made): B2J(?)3 = Blackburn Factory, 1962, 3rd week of October.

Brimar ECC83 preamp valves: 5I2/1574 = 5th week of September 1962. The second character of "5I2" is a letter "I" denoting September. 1574 is the code for ECC83.

The latest determinable date code in the amp is therefore 4th week of 1963 - main filter cap ("YTI").

Clearly one does not know how soon after production Hunts sent capacitors to Erith or how long it took for components newly arrived at Erith to find their way from store there to the work benches. The idea that it was only "a month or so" does not really wash. And it so much depends on what one is talking about. Woden transformers with January 1964 date codes ("AV") are still found for instance in amps produced in the middle of the year.

Preamp

General view.

Hunts bypass cap. date code "SWH" = 51st week of 1962.

Hunts bypass cap. date code "SWH" = 51st week of 1962.

Egen pots with code "AK" = Jan. 1963.

Main preamp filter cap, Hunts date code "YTI" = 4th week of 1963.

Still the old-style circular footswitch.

Power section

Three date codes visible in the power section. "TM" = December 1962 on the green Welwyn resistor; "YWI" on the 32uf Hunts capacitor = 1st week of 1963; "ISH" = 35th week of 1962.

The other thing to say is that the value of the green Welwyn wirewound cathode resistor is 82R, and its date code "TL" = November 1962:

The Welwyn date code "TL"(= November 1962) visible in the mirror. The power rating of the resistor is marked as being 4-5 watts

82ohms was the actual value used for the cathode resistor through to mid 1963, when one of 50ohms was introduced to run the valves harder and squeeze a little more power from the circuit.

Detail from sheet OA/26, the cathode resistor marked in red.

Note added 14th June 1963 signalling the change from 80ohms (recte 82ohms) to 50ohms.

Valves

The valves fitted at factory were Brimars. The ECC83s were made at the Foots Cray works, near Sidcup; the GZ34 was produced for Brimar by Mullard.

The manufacturing date codes, as mentioned above, are: 3rd week of October 1962 for the GZ34, and the fifth week of September for the ECC83s.

For the Burndept factory, having a supplier close by will have been a real boon. Quite whether Westrex, the other contractor charged with assembling AC30 chassis, also fitted Brimar valves to the chassis it produced is not known at present. The Westrex factory was in North London (Dollis Hill).

Just to add that the EL84s in the chassis were replaced at some point after 1965 (the replacements have Mullard date codes for that year). The originals are likely also to have been Brimars, though.

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