Reading MT/ST Tapes

Paul Berger phb.hfx at
Sat Jul 31 12:40:24 CDT 2021

On 2021-07-31 1:19 p.m., Chuck Guzis via cctalk wrote:
> On 7/31/21 8:55 AM, Paul Berger via cctalk wrote:
>> Since there was still a few 360s around when I started I also got to see
>> the inside of a 1052 a few times, they are a really stripped down
>> keyboardless selectric.  They used a function cam to space and since
>> they did not have a tab rack they would space a lot which would cause
>> the space cam to wear, I remember one that was so worn  that when it
>> cycled it wobbled very noticeably, the customer would not let us replace
>> it as this was the console for the 360 and they did not want it
>> unavailable for the time it would take to replace it.  Some customers
>> apparently would have a spare 1052 onsite.  The keyboard on the 1052 is
>> the keyboard from a keypunch machine.
> Did the 1620 Mod II and the 1130 use the same Selectric mechanism as the
> S/260 1052?  I remember that the Model B on the CADET always felt as if
> it would shake itself to pieces every time the carriage returned.
> And given the relatively high failure rate for motor drive belts, why
> did IBM persist in making replacement such a bugger of a job?
> --Chuck
I have never seen either of these machines but looking at pictures of 
them it looks like the first version of 1620 had a type bar typewriter 
as a console.  These type bar machine would have a common heritage with 
the Flexowriters both are descendants of the  Electromatic company that 
IBM purchased in 1932 but later sold off what became Flexowriter due to 
anti-trust concerns.

I did find a picture of a 1620 that does appear to have a selectric for 
a console and it looks like it is a modified OP selectric even being in 
the same case sunk into the desk so I suspect that it is the first 
version of the selectric I/O.

The console on the 1130 does however look like it is a 1052 that has 
been integrated into the machine.

Speaking of shaking apart on carriage return, I was once preparing some 
cash registers for the local phone company in a room where the had a HP 
mini that apparent ran some terminals for their subsidiary phone company 
in Prince Edward Island.  This HP had an ASR-33 for a console and it 
seemed that it printed a line for every transaction and when it would 
return it would slam into the dashpot on the left frame and the whole 
ASR-33 would rock. This mini recorded transactions on punched tape that 
was taken downstairs to the main computer room where it was read into 
the IBM mainframe on a high speed punched tape reader that looked like a 
3430  tape drive with the magnet head replaced by an optical head.

With regard to the position of the belt it is where it is because the 
selectric mechanism is split into two parts. On the left is the cycle 
shaft with the cams that position the type ball and through some gears 
turns the print shaft that drives the ball into the paper.  right in the 
middle running inside the appropriately named center bearing, is the hub 
that has the pulley on it that is driven by the motor this turn 
constantly.  on the left side of the the hub there is a torrington 
clutch  that when tripped turns the cycle shaft to print a character.  
On the right side of the hub is the operational shaft that turns all the 
time that have clutched cams on it to operate functions such as tab and 
backspace, plus another torrington clutch for carriage return, and on 
the extreme right a cam for shift that rotate the ball 180 degrees.  It 
would seem that the motor belt is positioned where it is so that the 
entire machine could be operated from a single motor.

On OP selectrics changing the belt is not such a big deal, you take out 
one of the gears that drives print shaft, remove the screws that hold 
the bearing plate on the left end of the cycle shaft and the either back 
off or remove entirely the cycle shaft. It was more of a challenge on 
the original I/O because of the presence of contact block both at the 
end of the cycle shaft and under the selection latches.  The original 
I/O was just a modified OP selectric That other than the addition of the 
contacts and magnets the only other change was the beefier capacitive 
start motor, I have seen this motor tear the teeth off a belt on a 
jammed machine just by turning it on.  You did not even have to look to 
tell if a belt was missing teeth, they had a telltale thumping noise you 
could hear as soon as you got close to it.

The I/O II was a lot better changing belts was pretty much the same  as 
an OP selectric and I don't recall having to change them as often.  The 
worst where the machines that where in a case like an OP selectric sunk 
into a desk, that case and mount just made things more difficult.

Part of the fun of the banking terminals was some bank branches had the 
machines on the counter, right where the banks customers are, and 
customers would often feel obliged to offer some of their wit or wisdom 
while you where up to you elbows in a greasy machine.  I those days of 
working on greasy mechanical machine we where obliged to wear suit and 
tie, but greasy machines where not the worst, for that there was proof 
machines with their purple indelible ink used to print endorsement 
stamps on documents. After working on them you would have purple hands 
for a few days.


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