using new technology on old machines

[Dave G4UGM]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at 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