Vox Defiant and Foundation Bass amplifiers have the same 50W power section in common. The schematic is OS/134.

Defiants can be found on this page and Foundation Basses here.

Detail from the JMI schematic for the Defiant / Foundation Bass power section. The transistors in question are the 2N3442 and 2N4347. Both types were in use from the beginning as the detail from the schematic above and surviving amps show. The 2N4347 is slightly less robust than its counterpart.

Extract from the RCA Transistor Manual of 1966.

Extract from the RCA Transistor Manual of 1975. The 2N3442 - 2N4347 - 2N6262 family.

DATE CODES

The number is the year, the month the accompanying letter: A-H = January-August; J-M = September-December. "I" was generally omitted.

Vox Defiant serial no. 1031. The date code of the 2N3442 is "6E" = May 1966.

Vox Defiant serial no. 1583 (still JMI). The date code of the 2N4347 is "7F" = June 1967.

Probably because they were cheaper, 2N4347s are more or less standard in the "Vox Sound Equipment Limited" and "Vox Sound Limited" period.

Vox Foundation Bass serial no. 2813, one of the last made. The date code of the 2N4347 is "2D" = March 1972.

Vox Defiant serial no. 2726 (around 100 or so from end of days). The date code of the 2N4347 is "7050" = 50th week of 1970.