Quad 405 clamp-circuit on the driver-boards

When did Quad integrate the clamp-circuit on the driver-boards?

In the 405-2 (from serial number 59001 on) with board-number M1265.3 the clamp-circuit was integrated on the driver-boards.

Some 405-1 (serial number between 57301 and 57600) as well as some 405's made in OEM for the BBC also have those new boards.

If you want a copy of the 405 service-manual in pdf, including the version definitions, send an e-mail to info@dadaelectronics.eu.

Stefaan