I have a really hard time getting excited about a
manual-pull paper
tape reader, though; I'd have to investigate some sort of power feed system.
The traditional way is to use a capstan and pinch roller, as in a tape
recorder. This gives constant speed, of course. The captan normally turns
continuously, the pinch rolelr is engaged by a solenoid to start the tape
moving. There was normally a brake, nothing more than an electromagnet on
one side of the tape and an amrature plate on the other side that grips
the tape when the electromagnet is energised, to stop the tape.
Yes, my HP PTR uses that method.
IIRC, the HP is somewhat unconventional here. The pinch roller is
controlled by a solenoid, but it is only off-tape dureing loading. When
the machine is in operatin, the pinch rolelr is enganged. The tape motion
is controlled by an electromagnetic clutch betwee nthe (shaded pole)
motor and the capstan.There is the normal brake design.
I managed to find a spare read head for mine on Ebay (totally
mis-descrived, which it probably why nobody else bid). The reader heads
can be taken apart and repaired (I've done it), but it;s ntot all that
easy. The main problem is that the plate carrying the phototransistors
has to be electrically isolate dfro mthe chassis, and there are various
'paper' insualtors you haev to get lined up. The trick is to make 2 metal
rods 1/8" diameter and about an inch long. Put those into 2 blind holes i
in the lower body of the read head (these hols are there solely for that
purpose), then fit the insualtors and phototransistor plate, fit the
screws and tightn up, then remove the pins. Fit the PCB and solder all
the wires in place.
I have
an optical PTR on one of my PDP-8s; it's an HP unit with a
homebrew board on the back that gives it a positive I/O bus interface
Possibly an 2748? I'ev got one on my HP9800s. There are a few pictures of
it on the HPCC ewb site...
Yup, that's the one.
As I said I have one, and I've taken it all apart and repaired various
bits. The main problem with mine was that the bearing in the magnetic
clutch had failed. The official repair is to change the complete clutch.
I made up some mandrels and dies and prssed the clutch apart in a bench
vice, and discovered the bearing was a stnadard size ball race. I had no
problems getting a new one and pressing it back in.
Electronically they are very simple. The 3 plug-in PCBs are basically
PSU, tape motion control and read amplifiers. I do find the amount of
hardwiring under the chassis to be moderately amusing....
talk to
the 8/e. That works nicely, and it's very fast. That, however,
is staying on the 8/e.
I didnt think it was _that_ fast.
Compared to my ASR-33 it's a screamer.
Checking, it's faster you you than me. I think you get 500cps out of it,
I get about 440 (due to the difference in mains frequency, the motor runs
slower over here). That's not bad, although I have things that are faster...
I think there's such a reader on Ebay at the momnet, if anyone's looking
for one.
-tony
