Odd Transistor Choice

Unless someone remember how much it costs in 1970s, we will never know why. However, when compares to the popular (and easy to remember) 2N2222, the 2A (vs. 0.8A) collector current seems attractive. Both are 250MHz, so freq response is probably not an issue.

Ft 250Mhz was not particularly special even then, the Ft is not relevant to the choice there; they chose because the V/Ic/Hfe etc fitted the need. Even the 60 year old BC107-109 family you probably know well had Ft of circa 200Mhz.

I guess 2N2218A/2219A or BFY50 would do as equivalents to 2N5859. There are zillions likely to work well.

piglet

They may have had commercial reasons to make that choice. Perhaps they were already buying millions to use in other products. Maybe an alternative that might have been a "better" choice would have added another part to the design. In many large companies there is a lot of pressure not to do that. John

Good point. Maybe also the low capacitances? Dunno.

I wish I knew WTF you were talking about.