A request from a non member

[Refugee]

There is little point in fitting another resistor until we are sure it is not going to burn.
The first thing I would do is to sort out that mains wiring. Have you got anything that is mains rated. Perhaps an extension lead for a computer power cable?

Then the low voltage side can be powered from the transformer and the bench power supply can be used to power the 40V side of it. 30V will do for testing the amplifier with an MP3 player as it will most likely shut the power supply down well before full volume is reached but this will not matter.
You can then safely touch on resistors while watching the currant.
It should produce something from the instrument circuit even at 30 volts but I can't vouch for this.
Once the amplifier is tested I would expect it to work with the bench power supply feeding the instrument end of the missing resistor as this point on the circuit will be at a lower voltage such as 12 or 24 volts at less than an amp.
Then we can work out the value and power of the resistor for you from the currant reading on the bench power supply.