Supply voltage for 2N2/256-BSCP

woodelf bfranchuk at
Thu Jan 17 16:46:09 CST 2008

Brent Hilpert wrote:
> "Roy J. Tellason" wrote:
>>> A year or two ago there was a discussion on the list where we were testing
>>> a variety of 74x175's (albeit configured in an odd manner) for some PDP-8
>>> front panel and were observing changing and idiosyncratic behaviour over a
>>> very narrow operating voltage range.
>> Do you recall offhand what sorts of changes in behavior was being discussed?
> Look in the archives around Aug/Sep 2006 for subject with
>   "PDP-8m Console Switch Problems"
> The gist was that the front panel was using the '175 in a non-specified way
> (FF collector triggerring) and a replacement device did not function in the same
> way. It turned out that the behaviour could vary with small changes in Vcc amongst
> devices from different manufacturers and different classes (74,74S,74LS).
> .. just an instance of device behaviour being sensitive to small Vcc variation.
> On the other hand, the early HP2100-series processors use some 74xx TTL
> operating at 4.5V on IO/interface boards, which is outside the Vcc spec.
> I've been a little surprised at HP for doing that.
>>> I hope you're not looking to mimic TTL - you'll have trouble sourcing
>>> multi-emitter transistors in discrete form.
>> I seem to recall some wikipedia page referring to those as if they ever were
>> actually available.  Not that I could say with any certainty that they
>> weren't,  and if anybody knows otherwise please feel free to point me toward
>> info,  but I've never seen them,  or heard of them as discrete devices at
>> all.
> (Yes .. (my comment was intended as a bit of a joke))
>  ---
> I've never seen the documentation for DEC's early discrete flip-chips
> (bitsavers?) but doesn't it include full specs for things like loading rules
> and fan-in-out, seeing as the flip-chips were sold as a 'logic family' to build
> one's own system from.
> Anyone know offhand how many transistors were in the first PDP-8? It's parallel
> and core-mem and thus outside the OP's objective but could be interesting for a
> ballpark comparison.

Well the PDP-8/S was about 1000 transistors so I am
guessing double that.

> (I know somebody on the list has a site listing all the -8 versions) but was
> the bit-serial version of the -8 done in discrete or IC? If IC, could be
> interesting to translate it back to discrete and estimate the transistor count.
A Ballpark guess may be 4 transistors per flip/chip and count the chips
in the classic PDP-8.

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