A hole punch is used to produce the first of 20 replica chassis. The chassis were produced at Teversham Engineering Ltd in Cambridge this week.
Photo: National Museum of Computing
Nick Heath is chief reporter for TechRepublic UK. He writes about the technology that IT-decision makers need to know about, and the latest happenings in the European tech scene.
As those of us who once repaired granny's wireless set will know, the high voltage was a problem not so much for the valves as for the passive components. Insulating materials were not nearly as good as today, and they were usually based on shellac. Part of the skill of good design was ensuring that a fault such as a short-circuited blocking capacitor didn't take a cascade of valves with it. Draw grid current and the valve will soon be dead, and valves weren't cheap. Mains transformers with 350-0-350 V secondaries would often go up in smoke. I remember when working in medical research during the 1970s having to resurrect some old radioactivity counting gear. It had hundreds of valves, and of course those impressive power supplies. There was also a mercury delay line, presumably of the same design as the ones in the early computers.
I have one of the Univac chassis, sans no tubes. I'm not about to part with it as I've had it for 50 years. Along with a bunch of Honeywell parts from a unit that used the miniture vacuum tubes hard wired to a card. Computing power had to be close to a one second clock. Tubes don't respond as quickly as a semiconductor. Memory?? How about punched paper tape. A loop to load the booter, another for system and another for a 15 step program. Initially used to calculate the trajectory of artilary shells, it replaced a large mechanical computer (servos and gears).
It is a valiant aim. As the beginning of computer technology you can expect the modest computing power. The very real problems running a machine of this kind are the voltages involved - none of your gentle 5v here! Valves run at high voltages - sometimes up to 400v. Oh, and they are prone to breaking down. Only replacing them was no easy matter with voltages like that flying around. Something for all of us to remember when our handy laptops go wrong.
I serviced domestic radios etc thru the war capacitors and resistors were the biggest problem and the resistor problem was not really solved till the seventies, the introduction of all glass valve's introduced a new problem with poor contacts with the sockets (Russian ones were best with gold plated pins) with the all too familiar problem of having to bang the TV to make it work.
Most of the communications equipment I maintained early in my career operated at voltages well above 400V. And replacing the tubes was an easy matter, as removing power stopped all that voltage "flying around".
I am sure that replacing tubes was a piece of cake. Only shutting the system down three or four times a day to accommodate this will have had repercussions? Oh, and I met those guys who tried changing them without shutting down to save time ... no visible scars but a few tales to tell.
if that often. Even our least reliable tubes were good for a month or two. When we had to replace tubes, each section was separately powered, so we could shut them down individually. And attempting to replace a tube without removing power from the system either got you a reputation as the electronics tech equivalent to "script kiddie" or a very nice wake at which your former co-workers consumed mass quantities and stood around shaking their heads and saying "What an idjit."