After some years of operation the amp refuses to operate suddenly, the heater supply seems to be gone. After opening the chassis the root cause can be seen immediatlely:

Yes, this reminds one about the design error of the original amp: The Molex KK connectors are just specified for a current of 5A, whilst four EL34 are consuming 6A.

The required repair includes removing the burned socket and connector and implement an off-board heater supply protection.

This is the result:

Everything is now desined for a continous current of 10A.

And integrated:

Insert tubes, adjust operating point and listen - it works again!