25 Sep
1997
25 Sep
'97
7:04 a.m.
Many collectors have multiple systems and peripherals that can be
cannibalized for parts if anything in their primary machine fails,
but what about maintaining an inventory of discrete components such
as ICs or those 150,000 Mfd filter capacitors?
I reviewed the availability of parts for many of my systems and found
that most components are readily available. Others were more difficult
to locate or were listed under another industry part number (e.g., a
"25LS2521" is actually a "74LS688").
Do you think it's worth the effort to purchase spare discrete components?
Are there any specific categories of devices or parts that are prone to
damage, failure, or extinction?
Regards,
Jason Brady jrbrady(a)delphi.com Seattle, WA
25 Sep
25 Sep
7:42 a.m.
Many collectors have multiple systems and peripherals
that can be
cannibalized for parts if anything in their primary machine fails,
but what about maintaining an inventory of discrete components such
as ICs or those 150,000 Mfd filter capacitors?
It really depends on you. Many of us are packrats that keep just about
anything more useful than a burnt out light bulb. Others do not want to
keep anything other than common spares. Your space has much to do with
this.
By all means, use this list for parts requests! Unless what you need is
truely exotic, I think (hope) most of us would sell the spare for the
price of postage (at least that is how much of the old ham radio community
works).
I reviewed the availability of parts for many of my
systems and found
that most components are readily available. Others were more difficult
to locate or were listed under another industry part number (e.g., a
"25LS2521" is actually a "74LS688").
Yes, just about any (non-custom) chip can be found if you look. Even many
of the extremely obsolete numbers (700 series RTL, 300 series ECL,
etc.) are not impossible (hard, yes) to find.
Do you think it's worth the effort to purchase
spare discrete components?
I keep quite a stock of chips and discrete components around, probably
more than most people. I also keep old boards so I can pluck out chips as
needed (I just found some early seventies boards loaded with 900 series
DTL and 9N00 series TTL, all in cerdips. Will I start removing the chips?
No, not now - the boards they are in make handy carriers.). Of course,
keeping an inventory is for the well discplined - something I need to work
at.
Are there any specific categories of devices or parts
that are prone to
damage, failure, or extinction?
^^^^^^^^^^^
There was a small thread about this when the list was very young. It is
probably worth starting again. Any takers?
I will start with a few:
Early or weird EPROMS: 1702s, 2704s, 2708s, 2516s, 2532s.
Early glue: 300 series ECL, 400 and 4000 series TTL, 700 series RTL, 1000
series ECL, 800 and 900 series DTL.
Glue made by unusual companies: Philco and Sylvania.
Early microprocessors: 8080 (they are drying up!), 6800 series support
chips (6810, 6830, 6859, etc.). Also, early (licensed) clones, like
the 9080, and the Intersil 6100.
Early memory: 4K DRAMs (I forgot the numbers).
Analogs: 1402A (I think) core sense amplifier, in cans.
Transistors: 2N404, just about any pre 2N1000 parts.
Passives: Not many, most are still available.
Additions welcome!
William Donzelli
william(a)ans.net
12:07 p.m.
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1:37 p.m.
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(a)ans.net
26 Sep
26 Sep
2:44 a.m.
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2:17 p.m.
Fortunately they were not commonly used in old
computers either. I think Sun
used them on some Sun 3 boards (I seem to remember them when I was
looking inside my 3/260), but that's about the commonest place.
I did not see any on a 3/280 board, but then it could have been done by a
different engineering team.
Oh, of course. Second-hand chips are more of a risk
than second-hand
machines - the machines (and peripherals) can almost always be repaired
or used as a source of spares, but dead chips are useless.
Second hand chips better be cheap, especially if they have "reject"
stamped all over (yes, I have seen some people trying to sell stuff like
that!). A guy I knew back in Illinois would go and raid the
Rockwell/Collins surplus outlet and sell off the chips quite cheap ($1 for
a tube of 128Kx8 RadHard EEPROMS - that tube cost Rockwell $24,000!). He
would often have very bizarre chips (10G series GaAs, for example), many
mil-spec. Many had dots on them. After a bit of research, it turned out
that red dots meant dead chips, yellow dots meant cosmeticly flawed but
electically OK chips (Rockwell is as picky as IBM), and no dot meant new
surplus.
Be careful if you're buying tubes of PALs or OTP
PROMs. Often they have
been programmed with code that's totally useless to you and of course
they can't be erased. EPROMs are less of a risk there.
I never buy PALs unless I know the guy that is selling them.
I've never seen 24 pin ones. There were 16 pin
ones pinned out like a
4116 (but with the A7 line N/C), with multiplexed address lines and 22
pin ones with non-multiplexed address lines. I have a row of the latter
in an HP1350 graphics unit. But almost all the ones you find are one or
other of those.
Two pins too many - I meant 22 pins, on the odd 0.400 inch packages.
William Donzelli
william(a)ans.net
27 Sep
27 Sep
5:43 a.m.
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25 Sep
25 Sep
12:50 p.m.
On Thu, 25 Sep 1997, William Donzelli wrote:
It really depends on you. Many of us are packrats that
keep just about
anything more useful than a burnt out light bulb. Others do not want to
keep anything other than common spares. Your space has much to do with
this.
You throw away your burnt-out light bulbs?
Sam Alternate e-mail: dastar(a)siconic.com
-------------------------------------------------------------------------------
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7:46 a.m.
Jason R. Brady wrote:
Many collectors have multiple systems and peripherals
that can be
cannibalized for parts if anything in their primary machine fails,
Do you think it's worth the effort to purchase spare discrete components?
Are there any specific categories of devices or parts that are prone to
damage, failure, or extinction?
Right now, I tend to think in terms of the early hard-to-get parts such as
the early memory chips and constantly ask about old, obsolete parts. It
would be useful to have a list of the parts that are hard to obtain such as
the 4004 and 8008 microprocessors, 1101 memory chips, and a few others I
can't recall off the top of my head. While I used to give parts away just
to get rid of them, that has changed and I try to stockpile known good chips
now. Will they ever be used and is worth the effort? Darned if I know :).
10:46 a.m.
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11:53 a.m.
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10 comments
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ard＠p850ug1.demon.co.uk -
dastar＠crl.com -
jrbrady＠delphi.com -
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william＠ans.net