Spare Discrete Components?

From: William Donzelli <william_at_ans.net>
Date: Thu Sep 25 20:37:57 1997

> And a programmer for same :-)
> Remmber that a 2764 and a trivial kludge-board (which can even be made on
> stripboard) will replace the 2704 onwards. Not historically accurate, but
> it may get the machine working again

Most EPROMs are socketed anyway, so such a hack is completely reverseable.
 
> PALs - particularly the XOR ones like the 16X4. The common GALs won't
> replace these, although I noticed that Lattice do sell a GAL with XOR
> terms. No idea what to program in on, though.

Come to think of it, XOR term PALs really are not very common. The others
tend to be, but in ten or so years, may be quite rare.
 
> Ditto 4 bit (4004, 4040) and support devices, the Intel 8008 (esp if
> you're a DEC enthusiast with a number of 11/34's to maintain - it's used
> on the front panel controller), 65xx support chips (6532, etc) (esp if
> you're a CBM person), TI 99xx, AMD2900, Intel 3000 (bit-slice chips),
> Zilog Z8000 and support chips, etc.

Sorry about exluding the very early Intel stuff - how could I forget!

I see quite a bit of the 65xx support chips - perhaps they are not very
rare were I used to live (Chicago area).

For those confused, I meant to say 6850, not 6859. The Motorola 6859 is
probably the hardest support chip to find of them all - it is the DES chip
for the 6800. I am sure that none left this country (at least legally).
 
> It depends on the machines you work on. If you're a home-computer
> collector there's little point in getting piles of 29xx bit-slice chips.
> PERQ fanatics probably don't need any Intel CPUs, etc.

Yes, but if you find a tube of useless (to you) raries for buck, you might
as well get them! Otherwise they might end up at the chip choppers.

> 4027? or some permutation of those digits.

There are lots, all very similar. Most are in 24 pin DIPs.
 
> _Most_ transistors can be substituted if you realise why the original one
> was chosen and have a good set of transistor data. A curve tracer (like a
> Tektronix 575) can be useful for determining the characteristics of an
> unknown (but working) device.

I understand that most any similar transistor will work in the old
machines, as the logic gates were designed to handle the huge swings in
quality the transistors had in the early 1960s.

It is nice to have matching originals, as some of the transistors of the
period were a bit odd looking.

William Donzelli
william_at_ans.net
Received on Thu Sep 25 1997 - 20:37:57 BST