Saturday, December 16, 2017

Miscellaneous projects and tests


We had a short session on Friday and consequently only had time for a few tasks.

HP 2116 in rack

We used a hydraulic lifting cart I brought over to lift the extremely heavy HP 2116 computer up high enough to slide into the rack. It may weigh 200 pounds and is unwieldy to lift. The computer is installed now, ready to begin restoration activities.

It was cleaned and examined closely. We found it had 16K words of core memory installed, which is the largest configuration that fits solely in the processor cabinet. Some machines could be expanded up to 32K words but the extra memory had to be housed in an additional module.

IBM 705 (or 702) tube module experimentation

I have a tube module from my private collection which we believe was used in an IBM 705 commercial computer. The module could have been used in the 702 system but the total numbers of 705 systems dwarfed the shipments of 702 machines, thus it is most likely from a 705.

The unit mounts eight vacuum tubes on a frame with components wired below the tube sockets. Man types of these existed, but we worked with the one that I had bought years ago on ebay.
An example of a module from a 702 or 705 system
Ken Shirriff traced the wiring and determined that my module implements five contact debouncers and five cathode follower driver circuits. The picture above is NOT my unit. Ken also owns a sample module, but his is more like the one pictured, having glass diodes and implementing a number of logic gates.

We are going to hook up the module and demonstrate it operating, taking a pushbutton or other noisy mechanical contact input and producing a cleaned up single pulse output. The cathode follower stage will drive a neon lamp, a typical role of that circuit in a 705 system. Think of this module as supporting operator console pushbuttons and display lights.

We will use -60, -120 and +120V power supplies to energize the circuits. Our input will be a lower voltage source through the switch, perhaps 10 or 20V. We expect to take pictures of this and release a Youtube video. If this goes well we will look at a more ambitious demonstration of the logic gates from Ken's module.

Alto Ethernet Tool tests

Al Kossow built a few of the ethernet tool units and came over to get Ken's latest firmware and test them out on the Alto. Ken had discovered the need for an impedance matching resistor on his boards, something not included in the plans used by Al, because when Ken used longer ethernet cables the Alto failed to reliably detect signals from his board. With the resistor added to Al's modules, they worked just as well with a variety of ethernet cables.

One of Ken's boards, prior to install of terminating resistor
The tool will do routing of communications but still lacks bridging, where the Alto hooked to a tool can communicate with other Altos (and tools) acting as part of a single Alto network segment. Routing will allow different network segments to communicate, a related but different functionality. Once the bridging support is working it will be flashed into all the network boards in use.

No comments:

Post a Comment