I managed to grab a few hours over the weekend to start planning the build of the PDP-9 racks. I’ve decided to build the frame out of 33×33mm planned timber which should give a nice rigid frame and be able to bare a few heavy items such as a paper tape drive.

The diagram below shows a sketch of what I am planning to build (hopefully you can read m left paw scrawl):

All the timber has been bought so next job is the fun bit, building it!

So after 18 months of hibernation, I’ve decided the time has come to start building my replica PDP-9. As I’ve previously discussed this is going to be based around my original PDP-9 console and use the simh emulator to implement the CPU.

Peripheral wise, the machine will feature a non DEC paper tape drive together with a pair of TU55 drives which I ultimately hope to hook up to the emulator.

Ourwardly I aim to make the machine look as close to the original as possible although under the skin the truth will quickly become obvious.

The first step is build the racks. I’m intending to build these in timber to keep cost and weight down. To enable me to start planning the dimensions, I’ve extracted the following from various DEC documents which give some clues as to the dimensions (note all are in inches):

The plan is to build a twin rack frame as illustrated below so as to enable the paper tape and TU55s to be mounted:

I’ve finally taken possession of the PDP-9 console I’ve been saving for for the last few months. It didn’t come cheap, but for such a unique item I was prepared to dig deep. My plan now is to rebuild a replica rack and hook up a simh emulator to the console. I will avoid making any modifications to the console so its left in original condition.

Along with the console, I’m also look at the feasibility of hooking up a TU55 drive, a paper tape drive and a deflection monitor
Along with the console I also aquired a set of 5 ex-PDP-12 backplanes and numerous flip chips so in the long term I am toying with the idea of building a TTL 18-bit processor. Whilst still not a true PDP-9 it would be an interesting exercise and a good bit more authentic than running an emulator.

Next steps are to start to draw up plans for the rack.

Introduction

Introduced in 1966, the PDP-9 was a 18 bit minicomputer built by Digital (DEC). The machine was a successor to the PDP-7 minicomputer, which it was upwardly compatible with and had roughly double the performance of the earlier machine. The machine could address up to 32KW of core memory.

The PDP-9 was one of the first small/medium sized computers to feature a keyboard/monitor system (a rudimentary for of operating system) which ran on the DECtape storage system.

The PDP-9/L, a compact and lower cost version of the PDP-9 was introduced in 1968. Of the 450 PDP-9s produced, 40 were PDP-9/Ls.

The PDP-9 was replaced by the TTL based PDP-15 in 1969.

Options and Peripherals