[vcf-midatlantic] New member, Intro

Herb Johnson hjohnson at retrotechnology.info
Wed Sep 14 09:52:31 EDT 2016

Thanks for your intro, and links to your Web site and vintage computers. 
I'll briefly make some comments (in my opinion) about the computers you 
have. But in general, if you do homework and identify the various cards 
and items in your computers, that info will tell you a lot about what 
you have and what you might do with it. "Homework" is my preference to 
"chat", speaking for myself.

The IMSAI is filled with Cromemco cards, so essentially you have a 
Cromemco Z-80 S-100 system, with a 4FDC floppy controller. that 4FDC 
determines what you can do with that particular set of cards, and what 
you'll need to find to create a CP/M system around it.

The PDP-8/e looks nice, and apparently you've powered it. Very old power 
supplies ought to have their caps "reconditioned", and you might check 
the DC ripple on both the 8 and the IMSAI to make sure the big caps are 
doing their job.


A Web search will find more pages on my site, on S-100 or PDP-8s.

There's lots of non-DEC cards in your 8; you might try to identify them 
by brand and model (ECRM?). You'll need (to identify) some kind of 
serial card, to talk to your 8. It would be convenient, to have an HTML 
document on your Web page which contains that information, linking to 
your photos. With that info on your Web page, others may find your 8 and 
cards, and contact you to your benefit. It would appear your 8 was an 
industrial controller, so those non-DEC cards ran something.

The fun of 70's vintage computing, is to reverse-engineer items you 
don't have docs for - in my opinion. Chips and connectors, special 
function devices, connections back to the bus - those are clues as to 
function and operation. These days, the Web is informative. You'll find 
the PDP-8 world is very different from the S-100 world, a generational 

Your post said you were not so interested in the industrial cabinets. 
The Vector Graphics motherboard, is in a commercial cabinet and is 
mounted in a commercial card cage; just as the 8-inch drives are mounted 
in a commercial cabinet. Neither cabinet was a product of Vector 
Graphics Inc; so the principle of vintage preservation would not be 
violated if you removed the drives or the chassis from those cabinets. 
But there is a decent card cage and it would be a challenge to replace 
that; maybe you'll find a smaller cabinet for it. Again, you have nice 
industrial cabinets; but such things are out of vogue these day - maybe 
some ham will need them for a base station or repeater.

Modern folks are not fond of the old open-frame "brute force" S-100 
power supplies, they use switchers, but my preference is to use 
traditional power supplies in S-100 systems. Beware that unregulated 
supplies like that 1) will run at higher-than-standard S-100 DC voltage 
if lightly loaded and 2) will retain most of their voltage for some time 
after power-down (I see bleeder resistors on your big caps). There's 
ways to deal with those issues, my S-100 Web pages talk about such things.

All those statements are, of course, my opinions and views; you and 
others may think otherwise, or have other priorities, as can you. But 
the parts, caps and chips and such, function as designed and don't care 
about "opinions and priorities"; I hope my Web site represents the 
technology correctly.

Good luck with the IMSAI/Cromemco and PDP-8/e. There's no shortage of 
Web pages where these are discussed and documented. And many people own 
either and will chat about them. What you do and how, is a matter of 
your time and interests and skills; you can learn a lot about the 
technology behind these systems, and/or meet others who have similar stuff.

Herb Johnson

Herbert R. Johnson,  New Jersey USA
http://www.retrotechnology.com OR .net

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