RobS
Experienced Member
I'm interested that you consider shunt regulators to be inefficient but CVTs efficient. I was under the impression that CVTs were notorious for spewing out heat and EMR. Regarding the shunt regulators I don't know why Honeywell used them but it is probably, as I mentioned on the programming page of my website, that there are no right or wrong solutions, only appropriate and inappropriate ones and I can only guess why Honeywell's solution was appropriate, so here goes. The CVT in the PSU provided the primary stabilisation of the supply voltage and the shunt regulator mounted in the centre of the backplane completed the task. Being in between the logic boards where the power lines enter the backplane the regulator provided the best possible control of the voltage delivered to the boards, but that probably isn't the whole story. Located there it had two tasks, firstly to compensate for voltage variations caused by cables and dodgy connectors between it and the PSU and secondly to compensate for varying demand from the logic boards. If we assume that the first effect was relatively constant then the major dynamic effect came from the second. The shunt regulator solved the problem by sinking the excess current when many logic boards went idle and the effect of this was to maintain constant power consumption and therefore constant temperature within the backplane enclosure as well as putting a constant load on the PSU. For reliability of electronic equipment constant everything is good as one can easily design for it. Contrast this with a modern efficient computer which consumes varying amounts of power from moment to moment and uses variable speed fans to compensate for the temperature fluctations, or a complex switch mode PSU which is very efficient while it works but then commits suicide when it can't decide how to tackle a situation. That's no problem nowadays when there's always another computer close by to replace the one that's misbehaving, but in the commercial computing world of the 1960s reliability was much more important than efficiency. There are other arguments, such as the fact that a shunt regulator doesn't have to pass all the current for a device like a series regulator and it doesn't reduce the voltage at all when it's not needed to. Personally I'd be more concerned about the CVTs and apparently so were Honeywell. The PSU cooling fan is mounted separately from the PSU chassis and connected to it by a plug and lead, which includes a blocking loop which stops the PSU working if the fan is left unplugged, whereas the regulators were just plugged into the backplane along with all the other boards.
Anyway I don't think 1960s American equipment was designed with efficiency at the top of the list of requirements. As an example, the lights in the Honeywell display panels had current running through them all the time, just not enough to make the ones that were supposed to be off glow. Someone mentioned that they remembered that the display on the H200 seemed to react to signal variations much faster than those on other computers, which was probably for this reason. Other benefits were that the transistors controlling the lights only needed to sink part of the current to turn them on and the lights never cooled down so much and therefore lasted longer, another example of constant being a good thing. I reckon that in total the lights on an H200 panel consumed around 7 Amps at 14 Volts, that's almost 100 Watts, when they were all on, which actually only happened during initialisation, but they must have consumed a good proportion of that figure when they were all "off" as well, so a few amps sunk by a 5 Volt shunt regulator won't be a big issue. Rather than worrying about power consumption one should just use the computer in the winter and save on the central heating bill. The branch offices of the company where I worked had Honeywell Level 6 minicomputers which made good room heaters as well as doing the office work but the staff had to keep the windows open in the summer -- and those machines had complex multimode switch mode PSUs.
Regarding storage, I am hoping that my Dataplex machine is still serviceable. It has two magnetic card drives which use big cards the same size as punched cards, each card having 50 tracks with 256 bytes per track, making 12.5k bytes per card, a forerunner to the floppy disk drive. The Dataplex uses all 7400 ICs, the original full power series, not even the LS series, so it is reasonable technology to use with the H200. Its memory uses long serial shift register ICs which cycle continuously, so the machine just has to wait until the right byte comes around in the register cycle each time like a virtual disk drive. At least the machine was designed, patented and built by a British company and it has very few light bulbs and no shunt regulators or CVTs so far as I can remember.
Anyway I don't think 1960s American equipment was designed with efficiency at the top of the list of requirements. As an example, the lights in the Honeywell display panels had current running through them all the time, just not enough to make the ones that were supposed to be off glow. Someone mentioned that they remembered that the display on the H200 seemed to react to signal variations much faster than those on other computers, which was probably for this reason. Other benefits were that the transistors controlling the lights only needed to sink part of the current to turn them on and the lights never cooled down so much and therefore lasted longer, another example of constant being a good thing. I reckon that in total the lights on an H200 panel consumed around 7 Amps at 14 Volts, that's almost 100 Watts, when they were all on, which actually only happened during initialisation, but they must have consumed a good proportion of that figure when they were all "off" as well, so a few amps sunk by a 5 Volt shunt regulator won't be a big issue. Rather than worrying about power consumption one should just use the computer in the winter and save on the central heating bill. The branch offices of the company where I worked had Honeywell Level 6 minicomputers which made good room heaters as well as doing the office work but the staff had to keep the windows open in the summer -- and those machines had complex multimode switch mode PSUs.
Regarding storage, I am hoping that my Dataplex machine is still serviceable. It has two magnetic card drives which use big cards the same size as punched cards, each card having 50 tracks with 256 bytes per track, making 12.5k bytes per card, a forerunner to the floppy disk drive. The Dataplex uses all 7400 ICs, the original full power series, not even the LS series, so it is reasonable technology to use with the H200. Its memory uses long serial shift register ICs which cycle continuously, so the machine just has to wait until the right byte comes around in the register cycle each time like a virtual disk drive. At least the machine was designed, patented and built by a British company and it has very few light bulbs and no shunt regulators or CVTs so far as I can remember.