BBtheEE - I know almost nothing about the workings of the tape drives and was only going on the workings of the ones in the Keytape machines. Brian told me that the Keytape machines were built around refurbished standard tape drives, which explains why they had the vacuum tape feed systems already in those, but it is likely that any components not essential to the Keytape operations were stripped out to make maintenance simpler. With the lower tape speeds and possibly lower rewind speeds as well braking would not have been essential, so the features that you mentioned could all have easily been removed. However, as my hub units and motors show no signs if having ever had the brake hardware that you describe attached it is possible that the original units were replaced with simpler custom units designed specifically for the Keytape machines. I have the schematics for several models of the Keytape machines and the vacuum switches and motors were definitely directly connected with no intermediate circuitry, so we may just be talking about quite different devices that happened to use the same basic drive technology. While looking at those schematics I also noticed that the Keytape drives only had one emergency stop sensor in each vacuum channel, so there clearly were simplifications made.
Regarding the attached printer, we had two Keytape machines with these, which were IBM Selectric golf ball typewriters with heavy duty screened cables attaching them to the Keytapes, which directly drove the solenoids in the typewriters. The Keytape machines had to have the K-717 printer adaptor unit in them, which consisted of an auxiliary forty slot backplane containing the extra logic boards. Of course I have all the logic boards from our two K-717 units plus one of the auxiliary backplanes, which I now use as a test bed for circuits before wiring them up on my main backplanes in my computer. The driver boards for the solenoids are easily identifiable because they needed heftier transistors than usual to handle the current surges involved.
Prior to acquiring the Keytape machines our company used other earlier automated typewriter systems, some of which I also acquired. That is how I still have Flexowriter reader and punch components able to handle paper tape and a Dataplex machine central processor containing magnetic card drives. Of course the typewriters used by both those old systems virtually fell apart years ago. However, I did acquire two Wang daisy wheel printers in working order junked by the typing pool, so stripped one down to use for spare parts for the other one, which is still waiting for me to adapt it to use with my H200 one day. Of course the typing pool also gave me all their supply of printer ribbons as well and I bought a collection of compatible daisy wheels on eBay, so I have a good chance of getting the thing working if only I can lift it up as at my age getting something that heavy off the floor is probably beyond me.
Returning to the Keytape printers, our mainframe computer regularly produced tapes with large batches of prestige documents to be printed on them, so the keytape operators brought books or knitting to occupy their time while the Keytapes typed the documents. Of course the operators had to do all the other tasks involved in using a typewriter which didn't have automatic paper feeding or alignment, so they had to stay at their desks to keep the work flowing.
Brian just assumed that your "diagnostic tape" was a SADEH rather than a SYSFIL but now I know I can ask him whether they had similar boot records.
Regarding the necessity of a tape drive option to read IBM tapes, I had a subsequent email from Brian saying that he vaguely recalled IBM tapes using even parity while Honeywell ones used odd parity. If so then equally an IBM drive would need to have the option to read tapes having odd parity to read Honeywell tapes. Equally the longitudinal check characters at the ends of records created odd parity along each track on Honeywell tapes. He also stated that the tracks went from LSB to MSB then Parity across the tape with the LSB track nearest to you when mounted on a drive and the parity track furthest away. He also said that the first character on the tape would be the first 22 character in the boot record to be absolutely clear about what to expect.
The field engineers did regular preventative maintenance to catch developing errors before the users encountered them, so diagnostic tests would have pushed the systems to the limits compared to regular work. Therefore unless a machine had suffered a sudden serious malfunction rather than a weird intermittent one the diagnostics themselves had a pretty good chance of working and they were probably run in a set order that checked the machine functions with that in mind. I can remember Brian once telling me back in the 1960's that they had a test on the control memory that pushed up the chance of it overheating by hitting it with the fastest possible stresses that any program code could ever produce. Control memory burnout was a particular weakness of the H200 but the unusually high speed of the magnetic core control memory was also the machine's biggest selling point as it determined the machine's maximum speed.
Thanks for the info about the drawer fans. I was actually given a couple of the airflow detector switches to add to my collection by another engineer. You didn't mention the air filters though. Possibly the last working series 200 maintenance engineer in the world in Mechanicsburg PA disdainfully called them "rock catchers" because they didn't actually filter out fine dust. I had a similar one from a Keytape machine which was just layers of wire mesh which were regularly soaked in oil to catch particles in the air; at least that was the idea. These filter could be washed and re-oiled, so disposable filters weren't needed. I assume that these were at the bottom of the lowboy cabinets with the fans, so the fans must have blown the air upwards through the drawers, which would have been the natural direction for hot air to go. There was a gap all around the lowboy cabinets directly below the desktops, so the filters couldn't have been there and entirely unfiltered air would have gone in that way if the fans were sucking. They could also have sucked in papers left on top of the cabinets, which would have created an extra job for the engineers.
Brian said that the 2040 machines like the one at our science museum were slowed down versions of the 1250, which he reckoned had overheating problems because of the amount of logic packed into the lowboy cabinets. In contrast the basic model 200 didn't put out so much heat. He said that at some sites with 1250's running intensely active applications it was necessary to prop the tops of the cabinets open a couple of inches to keep the heat levels inside down. The 2040's were meant to last longer than the 1250's by running slower and cooler and the science museum machine has correspondingly slower peripherals, e.g. a 123 card reader instead of the usual 223 and a 122 printer instead of the usual 222. I can ask him which way the air went through the cabinets though as he spent very many years with it blowing around him. From my visits to the computer room I seem to remember the draught coming out at waist level through that gap.
When I had a much needed shower, it having been so appallingly hot here over the last few days, earlier today I found out that our shower has a serious problem that needs urgent attention, so that looks like my task for tomorrow. Back to real life then.
