Before we go on to discuss the assembly of the Mudlark amplifier, we should mention some of the chassis hardware and componentry in the design.

While the output transformer config-uration is unusual and was described last month, the 100V line output transformers employed are not cheap or inexpensive by any means. They employ quality M6 grain-orientated silicon steel laminations and interleaved windings, as used in the best conventional output transformers. As well, the transformers are mounted with their cores at right-angles to each other and have been fitted with copper straps. Both these measures have the effect of cancelling or greatly reducing residual leakage flux from the transformers which could otherwise prejudice the amplifier’s operation.

Above: inside the finished amplifier. The octal sockets mount on the rear of the PC board and protrude through matching holes in the chassis.

The extruded aluminium chassis gives several advantages apart from having an attractive appearance, with a fine-grooved finish on the top section. It is very rigid and strong, providing a stable platform for the large PC board which mounts underneath.

One major change which has been made to the under-chassis arrangement of the PC board involves the octal socket and matching plug which connects all the wiring to the chokes and transformers. In last month’s issue, this was shown with a cable which threaded under the board and into the transformer compartment on top of the chassis.

Now the wiring has been greatly simplified because the ceramic octal socket is mounted on the topside of the PC board, the same as the octal sockets for the output valves. Then, inside the transformer compartment, a short cable connects from the octal socket to the vertical PC board which accommodates the nine chokes.