[Mondial]

There are a lot of generic output transistors you can use to replace the originals. Are they the usual TO-3 metal NPN's?

If the supply voltage is less than 60 V, then 2N3055 comes to mind. It was a common output in the 60's and 70's and they are cheap and easily available.

I would not get the NTE replacements. They just rebrand common generic transistors and inflate the price.

If you give me a little more info I can probably suggest an available replacement. I designed consumer high end audio amps in the 80's and 90's. and have some experience in specifying outputs.