DEC PDP-8
S/N 13
Donated on 21-May-24
Deborah Monosson, President & CEO of Boston Financial and Equity Corporation donated this DEC Classic PDP-8. There is an American used Computer inventory tag on the back. Both Boston Financial and American Used Computer were founded by the famous Sonny Monosson.
This version of the PDP-8 is referred to as a Straight or Classic PDP-8 because it is the first version. It was introduced on 22 March 1965 at the IEEE Show in New York. It typically use a Teletype ASR-33 terminal as the console. It could load and save ASCII and binary files using the paper tape reader and punch on the Teletype. This one is the "desktop" version even though it weighs about 200 pounds. The front panel made of made of silkscreened glass, and in the covers are made from tinted Acrylic, It has 4K 12-bit words of core memory on the left side of the chassis. The memory can be expanded to 32k words with external chassis. The linear power supply is behind the front panel. It is made of just discrete transistors and diodes using B, R, and S type FlipChips. More than 1,500 of these systems were sold.
The base price of the PDP-8 in 1967 was $18,000 ($171,546.02). Ours has the EAE Multiply/Divide option that cost an additional $3,500 ($33,356.17). The DF32 disk that we plan to add cost $6,000 ($57,182.01), and the three DS32 disk expanders that will be emulated cost an additional $9,000 ($85,773.01). The total system cost would have been $36,500 in 1967, or $347,857 now.
We plan to restore this system to operation, and add a DEC DF32 32k Word fixed-head disk. We will use modern circuitry to emulate the platter that holds the data in the DF32 disk. We can then run the 4k Disk Monitor from the DF32.
The PDP-8 circuitry is split into two parts. The right side holds the Processor, and the left side holds the Memory and I/O. There are connectors to add external core memory up to a total of 32k words, and to connect the I/O bus to peripheral controllers. The front panel is silkscreened glass. The pivot pins on some of the front panel switch paddles are broken and need to be repaired.
The sides of the chassis open to provide access to the backplane wiring. Two FlipChips were added in empty slots in the I/O-Memory side on the left. The white wires on the left were customer added, and are routed to boards on the Processor side on the right. You can see the power supply in the bottom of the chassis.
This is the left side of the chassis. The 4k Words of core memory is in the black box. The rest if the circuitry are for the core memory control and Teletype Console interface. Many of the empty slots are for the #183 Memory Extension Control and #188 Memory Parity options which are not installed. The empty slots at the far left are for the Memory Expansion cables and the I/O Bus cables.
There is an R405 in slot MF29 and an R303 in slot ME29 that is not described in the F-87 manual. There are white Wire-Wrap wires to these FlipChips and the also go to the Processor side of the chassis.
This is the right side of the chassis. All of this circuitry implements the processor. It even has the Extended Arithmetic Element that provides hardware multiply and divide. There are some modifications to the Processor that we need to document. The empty slots are for the #189 A-D Converter, KR01 Power Interrupt, and #681 Data Line Interface options that are not installed.
This is the back of the Type 708 power supply chassis. The Margin Check potentiometer and the -15VDC/+10VDC switch selects which margin power supply is in use. There are switches on the left and right chassis to disconnect the fixed power supply and connect the margin power supply to sections of the chassis. Adjusting the +10VDC higher than normal will find low-gain transistors, and adjusting the +10VDC power supply lower than normal will find high-leakage transistors.
It is now sitting on a short DEC cabinet. The DF32 disk will go in the empty location in the cabinet.