Hi 9-0-9,
I've made plenty of replacements for the 2SA798 - just use two matched PNP transistors and place them back-to-back with their emitter tied together.
Here are the transistors I use (I order at least 10 to end up with a matching pair).
Here's the circuit you need to build (the PNP one) to match transistors. I recommend ordering two 0.1%
resistors for your tester to avoid having to add a pot to make up the slight difference in resistance between the pair. You also have to have a +/- power supply (12-18V is fine) setup.
The 2SA798
pinout is BCECB, so it's easy to tie the emitters together. Some people epoxy or zip-tie the transistors together, but they are pretty much exposed to the same temperature within an enclosed case, so I haven't found a need to perform that extra step.
You can also use the same procedure to build 2SC1583 replacements; just use an NPN transistor such as
this one (and flip the diode and power supply in the transistor matching circuit).
Hope this helps!
- Andrew