Vox AC30 - Woden transformers

1962 - 1968

The AC30/6

Woden factory, Bilston, c. 1976. Picture from the .

This page will be for the time being a series of notes - mainly practical matters. There will be nothing, apart from this sentence, on the "tone" of transformers, an utterly nonsensical subject.

An overview of Haddon and Albion transformers can be found .

Woden date codes

It is perhaps worth saying as a preliminary that the Woden date codes relate solely to the manufacture of the transformers - they do not give the date of production of the AC30. Having been sent down to Kent from Bilston, batches could sit on stock-room shelves in Dartford and Erith for some time before being wired up into chassis. And of course, we do not know how long they sat on shelves at the Woden factory - presumably it took some time to assemble larger consignments.

The codes are simple enough - two letters. The second letter is for the year - "T" = 1962, "U" = 1963, "V" = 1964, "W" = 1965 and so on. The first is for the month - "A" = January, "B" = February, etc. "I", however, is omitted, so the sequence is "A-H" = January to August; "J-M" = September to December.

Above, mains transformer and choke with the date code "HT" = August 1962. Output transformer: "JT" = September 1962.

Wodens are mainly found on the chassis assembled by Burndept for JMI, extremely rarely on those assembled by Westrex, JMI's other main contractor.

The earliest date code that has come to light in an AC30 is "HT" = August 1962. Burndept began producing chassis for JMI soon after that.

From 1962-1964, Woden mains and output transformers have handsome sea-green enamelled shrouds. From 1964-1968, the shrouds are plain metal.

Prior to 1968, Woden evidently did not make transformers for JMI in March, that is to say, no date codes with "C" as the first letter have come to light in the period 1962-1967. All other months are encompassed though.

The Woden factory generally ran off batches of different types of transformer for JMI every three months or so, and in some instances every month - but not as a rule in March, as mentioned. The only Woden with a "C" for the month that has so far come to light is in a late Super Twin - serial number 5596, choke stamped "CZ" = March 1968.

JMI part numbers

As can be seen from the pictures above, the tops of the transformers were marked with JMI part numbers (for reordering) and date codes of manufacture. The date codes are NOT the date of manufacture of the AC30. Early part numbers - on tranformers with "HT" and "JT" date codes (August and September 1962) - are plain numbers:

Mains: 66309.

Output: 66310.

Choke: 66311.

Transformers with "HT" and "JT" codes are found in AC30s with serial numbers in the range 5630 to the 5700s, also in 6097.

At present, it appears that JMI did not use Wodens with October 1962 date codes ("KT") in any production amplifiers. A small batch of unused output transformers - stamped "KT" but of a new type - acquired by Alan Pyne (who had worked for JMI) look to have been (rejected) test samples.

With the advent of transformers with "LT" = November 1962 date codes, the designations changed. Wodens with these date codes first appear in AC30s made ready for sale in 1963, serial numbers 6172 through to the 8000s:

Mains: 66309 & J/82.

Output: 66310 & J/83.

Choke: 66311 & J/84.

In the autumn of 1963 however, the mains tranformer - 66309 & J/82 - was superceded by a new version designated 72318 & J/82. The suspicion is that JMI asked for the secondaries to be adjusted - specifically the main HT voltage. Batches of the new unit were produced with date codes "JU" = September 1963 through to "AV" = January 1964, that last batch being fairly sizeable. It is probably no coincidence that 72318 followed (in relatively short order) the modification of the cathode bias circuit (June 1963) - the main bias resistor changing from 80R to 50R.

Mains: 72318 & J/82. Date codes "JU" to "AV" = September 1963 to January 1964 and September (only) 1965.

In the late summer of 1964, at the request of JMI, Woden produced its transformers in a simplified (and therefore cheaper) form - the output transformer in particular, which had a less sophisticated internal structure. The new part numbers were:

Mains: 76852.

Output: 76853.

Choke: 76854. Also used in the Vox AC100.

Woden mains transformer produced in October 1964 = "KV". The plain metal shroud (instead of the enamelled green of the previous type) was doubtless a further means of cutting down on cost and time needed for production.

Batches

1962

In the table below, serial numbers, type of transformer (output, mains, choke), and date code are given. Just to recap, the second letter of the date code is year: "T" = 1962, "U" = 1963. The first letter is the month: "A-H" = January to August, "J-M" = September to December. Remember that the dates are the date of manufacture of the transformers, NOT of the amp.

Large batches of mains, outputs and chokes were ordered in the late summer of 1962 ("HT", "JT"), late 1962 ("LT", some "MT", and perhaps also the order for "AU") - quite how much time Woden needed to produce batches is not known at present.

5634: mains, output, choke "HT" = August 1962.

5648: mains, output, choke "HT" = August 1962.

5650: mains, output, choke "HT" = August 1962.

6097: mains and choke "HT" = August 1962; output "JT" = October 1962.

6664: mains, output, choke "HT" = August 1962.

6430: mains "LT" = November 1962.

6534: mains "MT" = December 1962.

Below, a detail from an AC30 output transformer made for JMI by Woden but not used in production. A batch of these was acquired by Alan Vale from Alan Pyne, a former member of JMI staff. They had been painted black.

Printed by Woden with JMI part number "67344", dated "KT" = September 1962.

There are several points of interest. First the JMI part number "67344". Woden normally numbered its transformers in a fixed order for Jennings: power transformer, then output, then choke. The set will therefore (notionally) have been 67343, 67344, and 67345.

Second, the transformer is early. The date code "KT" indicates September 1962. The previous set of Wodens - 66309, 66310 and 66311 - had been been ordered by JMI for use by Burndept in the summer of '62 - earliest date code "HT" = August 1962.

Third, the secondaries of "67444" are of the simpler type internally, single wires only emerging for the common, 8ohm and 16ohm taps - in this respect identical to the later set of Wodens used in production amps (76852, 76853, and 76854). 66310 has paired wires, following a more complex internal structure.

That JMI should have been exploring a cheaper set of transformers at such an early juncture is interesting. A simpler internal structure meant a cheaper unit. The more expensive set - 66309, 66310, 66311 - presumably won out on other counts.

So far there is no indication that 67343, 67344, or 67345 made their way together or separately into production amps.

1963

Large batches at the beginning of the year ("AU" and some "BU"), and late summer/autumn 1963 ("HU", "JU", "KU") - all for use in AC30s assembled by Burndept. A small batch of mains transformers came in in late 1963 ("MU"). Nothing has come to light so far with a date code in the period February to July 1963.

6716: mains, output, choke "AU" and "BU" = January and February 1963.

7061: output and choke "AU" = January 1963; "HU" = August 1963.

7109: mains, output, choke "AU" = January 1963.

unknown: mains, output, choke "AU" = January 1963.

8739: mains, output, choke "JU" = September 1963.

8922: output and choke "JU" = September 1963.

9434: mains, output, choke "KU" = October 1963.

9479: mains, output, choke "JU" = September 1963.

9677: mains "JU" = September 1963; output "LU" = November 1963..

9775: choke "HU" = August 1963; mains and output "JU" = September 1963.

unknown: mains, output, choke "KU" = October 1963.

9916: mains "KU" = October 1963.

9917: mains "HU" = August 1963; output "JU" = September 1963; choke "KU" = October 1963.

9986: output and choke "KU" = October 1963; mains "LU" = November 1963.

10317: choke "JU" = September 1963; output "KU" = October 1963; mains "MU" = December 1963.

10578: choke "JU" = September 1963; mains and output "MU" = December 1963.

Below, a number of AC30 Trebles from 1964 (serial numbers in the 11000s) with transfomers from 1963. Normal and Bass AC30s assembled by Burndept at this time have new Wodens (date codes "AV" and "BV"). It seems likely that the benches responsible for producing the Trebles were, at some point, supplied with older units to use up.

11718T: output "JU" = September 1963; choke "KU" = October 1963; mains transformer an Albion.

11769T: choke "HU" = August 1963; output "JU" = September 1963; mains"MU" = December 1963.

11873T: mains "MU" = December 1963; output and choke "AV" = January 1964.

11874T: choke "JU" = September 1963; mains and output "MU" = December 1963.

unknown Treble: output "KU" = September 1963; mains "MU" = December 1963.

unknown Treble: mains "MU" = December 1963; output and choke "AV" = January 1964.

unknown Treble: a strange assemblage - Twin cabinet, Super Twin serial number plate (Normal voicing), Treble chassis - choke "MU" = December 1963; mains and output "AV" = January 1964.

September 2025: updated

1964

Two large batches of transformers: early 1964 ("AV" and "BV"), and late summer ("HV", "JV" and "KV"). Albions and Parmekos were used for large runs in mid 1964 by both Burndept and Westrex.

Below, a quick overview of serial numbers and date codes. As ever, to remind that the date codes on the transformers are NOT the "date" of the AC30 in view.

Woden evidently supplied JMI with large batches of transformers in the autumn of 1964, good numbers still used for AC30s in mid and later 1965.

EARLY 1964

The part numbers on the Wodens manufactured in early 1964 are normally:

Mains: 72318 & J/82.

Output: 66310 & J/83.

Choke: 66311 & J/84.

Below, an overview (really a series of snapshots) of AC30s with Wodens made in early 1964, serial number of the amp first, then date codes etc. It should perhaps be said that the date codes were evidently not a primary concern on the assembly benches: one finds, at times, transformers made in 1963 and 1964 together in the same amp:

9781: mains, output, choke "AV" = January 1964.

9885: mains, output, choke "AV" = January 1964.

11613: mains and output "AV" = January 1964; choke "BV" = February 1964.

11873T: output and choke "AV" = January 1964; mains "MU" = December 1963.

unknown Treble: output and choke "AV" = January 1964; mains "MU" = December 1963.

12613: mains and output "AV" = January 1964; choke "BV" = February 1964.

12784: mains and output "AV" = January 1964; choke "BV" = February 1964.

LATER 1964 (overlapping substantially with 1965)

The part numbers on the Wodens manufactured in the late summer / autumn of 1964 are normally:

Mains: 76852.

Output: 76853.

Choke: 76854.

13031: output "JV" = September 1964. A question mark over this one. Choke and mains are Albions.

14832: mains and output "JV" = September 1964. Type of choke currently unknown.

14936: mains, output and choke "JV" = September 1964.

15054: mains "HV" = August 1964. Output transformer and choke codes / type unknown.

15881: output transformer and choke "HV" = August 1964. The mains is a Parmeko.

17116: both transformers and choke "KV" = October 1964.

18374: mains "JV" = September 1964; output and choke "KV" = October 1964.

19157: mains and output "KV" = October 1964; choke "HV" = August 1964.

20183: output "KV" = October 1964. The choke is a later gold-coloured unit stamped "66429" (see the section below). Type and date of mains transformer unknown.

20269: output "KV" = October 1964. The choke is a gold-coloured unit stamped "66429", the mains transformer a Parmeko.

September 2025: updated

1965 (overlapping substantially with 1966)

A note on the Woden transformers in AC30s, late 1965 / early 1966, serial numbers in the 20000s and 21000s - a sort of snapshot. At present, no transformers are known with date codes for January, February, or March 1965 ("AW", "BW", "CW"). Woden at this time was working to produce transformers for Vox AC80/100s.

The small number of AC30 chokes that have January and February '65 codes are likely to have been diverted from AC80/100 production. The two models used the same type (76854).

Part numbers, as in 1964, are normally:

Mains: 76852.

Output: 76853.

Choke: 76854.

The gold-coloured chokes used later on in this period in both AC30s and AC100s are normally un-dated. Only the JMI part number is stamped = "66429".

Also to record that in September 1965 one finds:

Mains ("JW"): 72318 J.82.

The 73218 J.82 is normally found in company with output transformers and chokes with standard part numbers. It is not known at present how or whether the 73218 J.82 differed from the 76852.

In the table below, serial numbers, type of transformer (output, mains, choke), and date code are given. Just to recap, the second letter of the date code is year: "V" = 1964, "W" = 1965, "X" = 1966. The first letter is the month: "A-H" = January to August, "J-M" = September to December.

Super Twin 4831: choke "AW" = January 1965; mains and output "KV" = October 1964.

Super Twin 4834: choke "AW" = January 1965; mains and output "KV" = October 1964.

19408: choke "DW" = April 1965; output unknown, mains an Albion.

Super Reverb Twin 3541: mains and choke "EW" = April 1965; output "JV" = September 1964.

Super Reverb Twin 3711: choke "EW" = April 1965; mains and output "KV" = October 1964.

20523: mains "JW" = September 1965; output "KV" = October 1964.

Super Reverb Twin 5301: choke "HW" = August 1965; mains "EW" = May 1965; output transformer unmarked.

Super Twin 5296: output "KW" = October 1965; mains "EW" = May 1965; choke "HW" = August 1965.

20750: mains "HW" = August 1965; output and choke "MW" = December 1965.

21086: mains and output "HW" = August 1965; choke "DX" = April 1966.

21098: mains "HW" = September 1965; output "KV" = October 1964; choke = "AX" = January 1966.

As can be seen, output transformers from October 1964 (code "KV") were still in store in early 1966. These had been ordered when serial numbers were in the 16000s. The batch was large - apparently no intervening date code (for output units) before August 1965 ("HW") has come to light.

Insofar as Super Twins are concerned, serial numbers 4744, 4784, 4831, and 4834 all have: mains and choke "KV" = October 1964; choke "AW" = January 1965. By the 5200s, date codes have become "KX"

Super Reverb Twin serial number 5301 has: mains "EW" = May 1965, and choke "HW" = August 1965.

September 2025: in progress

1966

The same part numbers as in 1965. The manufacturing date codes currently known are "AX" (choke only), "DX", "GX", "HX", "JX", "KX", "LX", and "MX" = January, July to December, probably increasingly small batches.

21019: mains and output "DX" = April 1966.

21086: choke "DX" = April 1966; mains and output "HW" = August 1965.

21098: choke = "AX" = January 1966; output "KV" = October 1964; mains "HW" = September 1965.

21192: mains, output, and choke "DX" = April 1966.

22177: choke "JX" = September 1966; output "KX" = October 1966; mains "LX" = November 1966.

22397: mains "JX" = September 1966; choke "MX" December 1966.

22563: output and choke "LX" = November 1966; mains "GX" July 1966.

September 2025: in progress

1967

Fairly limited production in 1967. The date codes currently known are "HY", "KY", and "LY" = August, October. and November.

21884: output and choke "HY" = August 1967; mains transformer replaced.

22765: mains, output, and choke "KY" = October 1967.

22789: mains, output, and choke "KY" = October 1967.

22841: mains, output, and choke "KY" = October 1967.

23061: mains "LY" = November 1967; choke "BZ" = February 1968. One of the last AC30 Twins produced and sold by JMI (also noted in the section below for 1968).

13270: mains "LY" = November 1967, a factory replacement in a much earlier amp.

1968

Manufacturing date codes only for February and March - "BZ" and "CZ". JMI was in the hands of the official receiver in early 1968, still operational but at substantially reduced levels.

22976: output "BZ" = February 1968. Choke and mains unknown.

23061: choke "BZ" = February 1968; mains "LY" = November 1967. One of the last AC30 Twins produced and sold by JMI.

Super Twin 5596: choke "CZ" = March 1968; output and mains "BZ" = February 1968.

Below, an interesting replacement Woden mains transformer in AC30 Super Twin 2731. In pencil on top: "Replaced / 9th July '68 / AG".

Unfortunately the fore-edge has rusted, so it is not possible to be sure of the date of the transformer's manufacture. But it will probably not be too far removed from the original unit in (very late JMI) Super Twin serial number 5596 - Woden date code "BZ" = February 1968.

AC30 Super Twin, serial number 2731.

AC30 Super Twin, serial number 5596.

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