SBC6120 PDP-8SBC6120 PDP-8
How YOU can own a Complete
PDP-8 Computer System


Bob Armstrong's SBC6120/FP6120 kits are once again available!!
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This web site's publication of my work with Bob Armstrong's
beautiful PDP-8 system generated sufficient interest
for one last iteration of this unique kit.

But when they are all gone this time,
they're almost certainly gone forever!

What's this all about?

If you have come to this page directly, and have not perused the companion
pages with their video demos, you might want to start at the beginning, and
also check out Bob Armstrong's Spare Time Gizmos SBC6120 page.

Bob's SBC6120, PDP-8 Single Board Computer kit, and its companion FP6120 front panel kit, are not continuously available because they are inherently low-volume specialty items of great interest to a few people. Even in production volumes of 50 to 100 units at a time, the kits' custom made components are much more expensive than they would be if they were produced in high volume. So these unique kits are primarily of interest to a rarefied population of true computing enthusiasts and computing history buffs. (I happen to think they are spectacularly cool! :)

To give you some idea of the sort of custom machining that goes into the components of these kits, here's an excerpt from a posting Bob Armstrong made on January 8th, 2009, as he was researching the possibility of producing another run of kits (this was the last run of kits from which I purchased three):

Excerpt from Bob Armstrong's 1/08/2009 “SpareTimeGizmos” Yahoo group posting:

I've had a meeting with the vendor that used to make the plastic faceplates for the FP6120, and they're willing to run 50 pieces for me one more time. Unfortunately the cost is almost double what it was previously, partly because of the lower quantity, and partly just because prices have gone up since 2003. The machine shop that did the LED light well bar has also agreed to do those again, so I can offer them as well. And I can offer PC boards and the two GALs for the front panel - that part is easy, at least.

The faceplates would be exactly the same as the last time around. They're silk screened in five colors onto the back side of a 2mm polycarbonate sheet, and then adhesive is applied with a special fixture that protects the LED windows. At the same time a 1/4" thick acrylic piece is laser cut and drilled to the necessary dimensions and then eight mounting standoffs are installed and glued into place. Finally the polycarbonate sheet is laminated to the acrylic panel and the whole thing is laser cut once again for the switch openings. Since the ink in the silk screen layer ends up sandwiched in between the polycarbonate sheet and the acrylic back panel, the graphics won't fade and are nearly indestructible. And since the mounting hardware is already installed the whole thing is ready to attach to the PC board.

The LED bar is a chunk of 5/8" PVC that serves as a light well for the LEDs. It prevents the light from, say the MA8 LED, from leaking into the windows for the MA7 or MA9 LEDs. It's actually machined out of a sheet of PVC stock and has some fairly complex geometry - In addition to the LED holes, the mounting holes are countersunk (since the front side is flush against the back of the faceplate) and, since the back side is flush against the PC board, several openings have to be machined into the back to clear components. It takes about 45 minutes on the CNC mill to make each one.

The PC boards are about 12.5" by 6.5", double sided, silk screened and solder masked, as usual. You can read all about the FP6120 construction in the FP6120 manual (not to be confused with the SBC6120 manual) -

... and a bit later in the same posting, Bob discusses the situation with the front panel kit's special-order white C&K paddle switches:

You can buy compatible switches as regular stock items from DigiKey, BUT they're rocker switches, not paddles, and they're black. Oh, and they cost $8.94 each (momentary) and $8.26 (non-momentary), for about $170 total. They'll fit mechanically, but the black rockers may not be the most attractive thing.

So, if enough people want, I will special order the correct paddle switches [from C&K] and include them in the kit. I'll sell them for exactly the same price as the DigiKey switches, however this way you'd get the same beautiful white paddle switches that you see on the original FP6120.

To get a better idea about the nature of the kits, you can download and read through the single-page brochures, assembly guide & user's manuals, and browse the schematics for both the SBC6120 single board computer and its companion FP6120 front panel:

The Situation Today:
WHILE THEY LAST, Bob Armstrong is offering a
combined SBC6120/FP6120 partial kit for $600.

See Bob's new page for all the details!
VERY IMPORTANT NOTE: Due to custom production turn-
around time, the kits will not be available for shipment until
mid-April. But Bob is accepting fully-paid pre-orders and
the kits will be allocated in first-paid-first-reserved order.

If you want to be sure to get one,
Please DO NOT WAIT to order and pay for it.

What's a “partial kit” ??

A partial kit consists of all of the custom-made, special-order, and hard-to-find bits and pieces required to assemble a complete, working PDP-8 single board computer with its matching front panel: This includes the printed circuit boards, a Harris Semiconductor HD6120 single-chip 12-bit PDP-8 microprocessor, all of the custom-programmed gate array logic (GAL/PLD) chips, RAM, and EPROMs containing the SBC's BT6120 BIOS code — essentially all of the real meat of the kits, consisting of everything that you can't otherwise order off-the-shelf from various online electronics suppliers:

The SBC6120 Single Board Computer portion will contain:
 The SBC6120 PC board (both sides solder masked plus silk screened legend),
one HD6120 PDP-8 CPU chip, three 64x4 SRAM chips, two pre-programmed
EPROMS with the BTS6120 firmware, and three pre-programmed PLD chips.
The FP6120 Front Panel portion will contain:
 The FP6120 PC board (both sides solder masked plus silk screened legend),
the front panel itself, the custom machined LED shadow bar, the two
pre-programmed GAL chips, a set of C&K switches, and the two mating bus
connectors.

You can find a complete bill-of-materials (BOM) at the back of each user manual. This combined parts list, excerpted from the back of both user manuals, shows with  yellow highlight  the parts Bob Armstrong will be supplying. You'll see that it also provides the supplier and stock numbers of everything else you'll need. So obtaining the rest of the bits and pieces should not be a problem.

If you aren't familiar with the terrific online sources for parts, you'll want to check them out too:


I should explain that Bob is not making money doing this, even with these partial kits priced at $600 each.

Just as I offer free software so that people can benefit from what I am able to create, Bob enjoys making these kits available at near his own cost. In case you haven't noticed, everything Bob creates is 100% open source and completely documented so that anyone can recreate his projects, from scratch, all on their own. ALL of the files need to re-create the entire kit — CAD files for the circuit boards, programming files for the EPROMS, PALs, GALs, and everything else — are ALL freely available on Bob's SpareTimeGizmos web site. And, frankly, if you would do it all yourself it would be a lot easier for Bob . . . and you would get all the benefit from everything Bob has created. At the bottom of this page are links to all of the design files and source code, free for the taking. But experience has shown that people are more comfortable purchasing those special custom pieces pre-programmed and ready-to-go. (I know that I was!) So, when enough people are interested, Bob offers to pull everything together for that group . . . but he's only covering his own direct costs.

This combined partial kit will ONLY provide the hard (or impossible!) to find bits & pieces, the custom-ordered and custom-made parts, circuit boards and programmable parts. You will still need to add IC sockets, resistors, resistor packs, capacitors, and so on, as detailed in the combined parts list. All of these things are readily available from the sources specified, and possibly your corner Radio Shack store. Moreover, the members of the SpareTimeGizmos Yahoo forum are generally very helpful and willing to help get you out of any tight spot.

A Single Source for all the REST of the Kits' Parts...

One of the guys (Robert Ribbeck) who has built Bob's kits in the past, who hangs out in the SpareTimeGizmos Yahoo! forum, and is well known to the people there, has stated that he will make up a kit of all of the rest of the parts required to complete the combined kit for anyone who would prefer to have him do the parts scrounging, leg work, and ordering. Robert has done this in the past for these and other partial kits, and everyone appears to have been satisfied with what they received.

He has stated that the cost for everything NOT provided by Bob Armstrong would be $175 with red LEDs, or $185 for the same white LEDs I used with my own kits. (This includes taxes. US shipping would add $10 and non-US shipping would add $35.) I prefer the white LEDs, since all PDP-8's up until the very last models — the 8/f and 8/m — used white incandescent lamps (the 8/f & 8/m did use red LEDs). The white LEDs, therefore, look a bit more authentic to me and somewhat less “electro-generic” <g>.

If you are interested in taking Robert Ribbeck up on his offer to round up everything else you'll need to complete the kits, you do not need to do anything about that now. Just know that the option will be available to you if you choose.

The next steps are up to you...



GRC's PDP-8 Pages:
CLICK HERE to learn how YOU can acquire & build
one of these complete PDP-8 systems for yourself !!!

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Last Edit: Feb 09, 2010 at 10:36 (2,744.90 days ago)Viewed 14 times per day