Herb's DEC PDP-8/f

[PDP-8 front panel]

My PDP-8/F which was acquired from Princeton University several years ago.In 2009 I started to pay attention to it in, thanks to my colleague David Gesswein. In May 2012 at a MARCH fix-it event, I opened it up and cleaned out most of the soft-foam cushioning and inspected the cards. In May 2013, David and I checked out the power supply, then the cards, and got the 8/f mostly running!

This page Last updated Jan 11 2014. To email me or to order, see see my ordering Web page for my email addresses. My other DEC stuff is on this linked Web page.

My PDP-8/F

PDP-8/F case view from the top. IN this top inside view of my PDP-8/F, you can see I have one backplane of 20 slots (5 blocks of four slots). The front panel is in "front". Behind the backplane is the power supply, in its black box with a small white connector sticking out. Space to the side of the backplane is not photographed, it extends from the back of the hex-width front panel to the back of the case. Typically, for more boards, another "expansion box" with a quad-width or hex-width backplane and power supply would be attached to this chassis.

Cards in my PDP-8/F, front to back

-- KC8F? - programmer's console (lights and switches)
-- M8330 - KK8E Timing board (system clock)
-- M8340 \_ optional KE8E EAE board 1
-- M8341 /  optional KE8E EAE board 2
-- M8310 \_ KK8E CPU control
-- M8300 /  KK8E CPU registers
-- M837  - KM8E or MC8E extended Memory & Time Share control
-- empty slot
-- M8655 - RS-232, 9600 baud TTY control, UART
-- empty
-- "blue tabs" board, Data Systems Design (later Qualogy) DSD 2131A-5, see below
-- empty
-- brown tab board, no clear brand, analog data collection.
-- M849  - KK8E RFI shield
-- empty
-- empty
-- black tab board, CESI brand board, prbably VM816 16K? memory
-- M8320 - KK8E Bus loads

Identifications above based on Omnibus Modules listing by Douglas Jones at the U.of Iowa. I've not verified the options (KKxx descriptions). A brief description of the 8/F Omnibus is at this Web site.

MARCH fix-it 2012 cleanup

I attended the MARCH fix-it event on June-July 2012 and brought my PDP-8/F there. There was not time or opportunity, to do more than clean up my PDP-8/F, and invite some comments by David Gesswein who was also resident and working on 8's himself. As he did with the MARCH PDP-8, I removed cards and vacuumed my machine. David noted mine was in pretty good condition, with little of the rust and debris of MARCH's 8. I removed the foam pad under the top, which David noted as a potential source for corrosion, gunk and shorts.

this top_first photos shows the 8/F when first opened on-site. Photos of the 8/F top_before cleaning versus top_after cleaning , are a cautionary check to make sure the boards are in the same order. I only removed some cards, to vacuum out the slots. There was very little debris, only flaked-off foam from the lid. Here's close-up's of the slots and the worst of the debris as I vacuumed.

front panel back

On Oct 2012, I did more work on the 8/F. Looking around the switching supply, I was able to see an inside label. It dates the 8/F to Dec 1973 and confirms it was a "L.D.P market" system. P/L# 84?

Power supply photo of the BC20-a power controller panel, on the back of the cabinet.
Power supply photo of internal J1 connector
Power supply photo, back cover removedshowing the component side.
The component layout matches the layout in the H740 documentation.
Power supply photos of the 10A fuse and
Power supply photo the 15A fuse.

Details on boards

CESI board

I have not examined the CESI in detail. Here's some possibly relevant links. This PDP-8 FAQ entry says "The OMNI-8 operating system supported the enlarged PDP-8 address space of the CESI (Computer Extension Systems Inc) memory cards...". That led me to a UMN .edu IT department's former Web site full of CESI documents. They are now archived as images courtesy of David Gesswein's PDP-8 Web site.

A document from umn.edu (University of Minnesota, USA) was a CESI VM816 product brochure. It describes a 4K to 16K memory board which looks like mine. Here's page one and here's page two.

When the 8/f was restored to operation in 2013, the board was operational, as a 16K memory card. It has 2141-4 RAM chips, no parity.

DSD controller board

The Non-DEC blue-tabs board I have in my 8/F is a "DSD 2131A-5" "PDP-8 Interface Board"

-- with blue paddles, quad width, all TTL small chips
-- one 20-pin connector w/9 active pins 10 gnds
-- device code 8,6,5,4,3 jumpered (device code 20? 57?)

THere are 5 rows of 8 or 9 TTL-type 14/16 pin chips. The 20-pin IDC connector has one row of ten grounded, the other row only 9 pins are in use. The text in quotes appears on the board.

According to a DSD 440/480 service manual, they made an 8-inch dual floppy controller which connected to PDP-11 or PDP-8 interface boards. The floppy controller for Shugart 800 or 850 drives was model 4440 or 4840, which used an Intel 8085 processor and a 12-bit 2911-based microcontroller.

David Gesswein of pdp8online.com says "[his own] controller is labled DSD A/2131-6. It looks like this is the controller for DSD [brand] 8" floppy drives." Here's David's page on the DSD product for the PDP-8. DSD's drive used an 8085 "formatter" board to run their drives via the DSD interface. Doug Jones's PDP8 site also mentions the DSD drives. Bitsavers has DSD manuals including a DS 440-480 series drive product manual, with a 2131 model PDP-8 interface board.

adac 600-8e analog data card

I did not look hard at this card until the 2013 restoration. It has a pair of modules on it. Closer examination identifies it as a adac corporation model 600-8e analog/digital card. The board has two adac brand modules. One is a das-12, 16 channel 12-bit analog to digital converter. The other is a adac brand PD-15 DC to DC voltage converter, probably supplying +15 volts for the A/D. There's a ribbon flat cable, presumably for the analog voltages.

H740 power supply

Quoting from Toby Russell on site pdp8.co.uk: "The PDP-8/M uses a H740 switch mode power supply that provides +15V @ 1A, +5V @ 17A, -15V @ 5A together with LTC-L, PWR OK L, PWK OK EN, AC LO L, and DC LO L signals. (It should be noted that not all of these signals are used within the PDP-8M). This power supply is also used within the 5.25? PDP-11/05 and PDP-11/10." I thought that H740 name sounded familiar....Toby "rebuilt" the caps by powering up for brief but increasingly longer periods of time. I may choose to pull the caps and charge them up separately. On Oct 2012, I coulda bought one on these on eBay "from a working environment" for $100 delivered.

May 2013 repairs

In May 2013, David Gesswein and I checked out the power supply, then the cards, and got the 8/f mostly running! The linked Web page tells it all.

Related PDP-8 stuff

PDP-8/E chassis

In May 2013, I acquired a PDP-8/E chassis with power supply, backplane, AC switch. Also the front panel PC board. I discuss the 8/E chassis and powering it up, on my May 2013 8/F fix-it page.


In April 2009 at the Trenton Computer Festival, I picked up this PDP-8 version of the RX02 floppy drive, from Mike Connor of NY The photo is on-site at TCF. Just goes to show, you can still get serious computing iron at TCF!

The RX02 uses a RX8E (M8357) interface board for PDP-8 use, which I guess I have to find to use this drive. Apparenly it can also be configured for the PDP-11 with a M8256 Unibus interface.

PDP-8 core memory

Among my core memory collection, in May 2009 I stumbled across this pair: a H219A core memory card and attached G649A Core x-y driver & sense/inhibit card. Don't know if they work of course; and "pdp-8.org"'s list of modules says this pair is too slow for an 8/E" and presumably for my 8/F.

However Philipp Hachtmann of Germany, a PDP-8 owner tells me his Lab8/E is running a H219A on an extension box, and encourages me to consider similar options.

From the Web, I see that some other PDP-8's have:

# M865 - 20ma, 110 baud TTY control
# M869 and M885 - Point plot display system
# M840 - High speed paper tape reader and punch
# G227, G619 and G104 - Core memory system, 4 k words (green handles)
# G227, G619 and G104 - Core memory system, 4 k words (green handles)
# M832 - Bus loads 


I acquired a tape drive several years ago, that looked like a DECtape drive. Turns out, it's a LINCtape drive - part of a LINC system developed before the PDP-8. DEC incorporated some LINC features in early PDP-8 products including a LINC/8 dual system. Look over my LINCtape drive and some of the correspondence and help I've had about and with it.

Other DEC equipment I have

Other DEC equipment I have is indexed on this DEC Web page.

Thank-you's and other PDP-8 sites

Many thanks for the support and advice I've recieved from David Gesswein of pdp-8.net. His site is an enormously valuable resources, and he's personally helped me with my PDP-8 and PDP-11 efforts. He's a contributor (as I have been) to the MARCH Vintage computer museum at InfoAge in Wall NJ.

MARCH Vintage Computer Museum at InfoAge in Wall NJ has a growing collection of DEC equipment. That includes a "straight 8", the original Flip-Chip PDP-8; and a PDP-11/20, which I documented and interpreted for them some years ago.

The Rhode Island Computer Museum, in North Kingstown, Rhode Island, USA has a number of PDP-8's in stages of restoration, among other computers. I've corresponded with them, and visited their facility several years ago.

I've chatted with Steve Lafferty, who acquired a PDP-8/M and restored it to operation. He's not put details of the 8/m restoration on his Web site, but he does have a RAM board project for the 8/M that's well described.

Herb Johnson
New Jersey, USA
follow this link to email @ me

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