Need help on Jadis JP-80

The burnt diodes in the power supply should be "zener diode" which provides the reference voltage for the regulator. Looks like they are identical. You may remove the other one in better shape to look for the part number printed on it.

Johnny

Thanks much Johnny. I pulled then out and foolishly misplaced them. Can anybody identify them? 

Here’s what I believe schematic of the voltage regulator would be. Surely, this is just my estimate from the information I found online. 

You can replace the two zener diodes like the 1N750 with 4.7V 200mA one and adjust the 47K pot to get 24Vdc at the output of the power transistor. 

As there are some other components got burnt in your preamp, all the components need to be checked if they are still good or defective.