Jim Brain asked: Questions: * Why was the darlington pair needed with the 2n3904/2n2222 setups but not with the 2sc1815/7406/7416 setups? Is the TIP29 that hard to toggle? The TIP29 has the gain(hFE) of a small brick typically, as low as 15 at current so I assume if I run the numbers that the 4401 is used to source more current when the TIP29 was on and to keep it in saturation at full current. If a small value resistor (higher current) was used to bias the TIP when on then the 2N3904 would have to sink too much current when the TIP29 was off to be practical. So it is hard to drive because it doesn't help that much by adding DC gain. * The 2n3904/2n2222 and TIP29 are commodity. Why did the VIC go with more specific transistors? They were overseas sourced, if they used US transistors they would have had to ship them from US to Japan for stuffing, plus more expensive in general. This was back when the Japanese were kings of the .5 cent transistor. * The 2n3904/2n2222 circuits have a 10K to ground on the first stage transistor base. I assume this weakly holds base at GND until a signal appears. This does not show on the VIC,64. Why not? My preference is always to tie something down to create a known voltage drop . With that said, the C64 was cost reduced by various entities, they would have known if not stuffing the part decreased yield if it existed in the first place. I didn't like the interaction of two transistors by the time you run min/max gains on both it felt a little sloppy, I designed it out on TED/Plus4 to use my favorite transistor... the output stage of an '06/'07 Bil Herd ******************************** -- Jim Brain firstname.lastname@example.org www.jbrain.com Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2012-02-17 07:00:18
Archive generated by hypermail 2.2.0.