> -----Original Message----- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of tony duell > Sent: 16 June 2015 17:29 > To: General Discussion: On-Topic and Off-Topic Posts > Subject: RE: using new technology on old machines > > > > > It's also that this is the 'classic computers' list. To me, classic > > > computing means rather more than just the hardware. It also covers > > > the design and construction methods, technology and so on. And there > > > seems to be precious little of that in a modern microcontroller > > > acting as a clock oscillator. > > > > > > There isn't., but some-times we have to compromise, and sometimes we > > choose to compromise. I looked at the circuit of the M484 and I might > > not have the parts in the parts box... > > I assume you mean M452 here, I can't find a reference to M484.
I did don't know where 484 came from > > I suspect many of the parts are not that critical. > I don't think so either, but I see from:- http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/m/m452.pd f that the original appears to use a 2k 10-turn pot, and a 7440 output buffer, neither of which are in my rather extensive junk box. In fact the 7440 are rather rare, and I see the cheapest I can get them for is around $4.00 each. I do however have a tube of pic 16f84 chips and a few 4Mhz crystals and so could build a suitable generator with 1 x IC and 1 xtal. The great thing about PIC, Arduino and FPGA is they allow the creation of something which is as functionally identical to the original as you can get without duplicating it. > > .. its also a nasty hybrid design with DC biased NPN and PNP > > transistors. I find it ugly and can see it being a pig to debug, > > though it simulates fine in LTspice... > > I didn't find it that hard to basically understand in my head. After all, there > are only 4 transistors, and 2 of those are just an output buffer. Quite why > having both NPN and PNP transistors makes it harder to understand I do not > know. I am really used to RF circuits so am puzzled there is no inductor. It kind of looks like a Darlington Pair but it isn't. What I don't understand is why the emitter of Q1 is spliced in what I assume is a voltage divider in the collector of q2. I was expecting a multivibrator circuit... > > I will leave the flames about Spice and simulation packages in general for > another day. You are touchy. Would it help if I used the original Spice2 written in Fortran IV. It still works. Sadly I don't have a real mainframe but have to use Hercules to run it.... > > -tony Dave
