You can use either on the AU-919, on the X1 A1837/C4793 might be a bit strained since they have to drive 3 pairs of outputs, and also A1930/C5171 have not only a higher Icmax, but also a higher Ft, so might be a better choice for the X1. However, I cannot be absolutely sure as I have not tried them.[/QUOTE
Thanks for your response. I am comparing more carefully the datasheets for the A1930/C5171 and A1837/C4793. It turns out that the SOA for the later is better despite of the fact that it is a 1 amp Icmax. I believe this is because of the larger value for the collector-emitter voltage. (230V for the A1837 versus 180V for the A1930) This seems marginal but it does widen the SOA. In the AU-919 the drivers are operating at almost 55V. Ag this voltage the A1837 can deliver nearly 200mA while the A1930 delivers about 100mA. According to this the A1837/C4793 pair is preferable, albeit with the limitation of the lower ft of 70MHz.
PS:
You have done some of the most amazing restoration works i am aware of. I have seen your thread on the AU-919 in the Croatian forum. Thanks for sharing your experience.