WTB: DEC PC04 Paper Tape Reader/Punch

Tony Duell ard at p850ug1.demon.co.uk
Mon Aug 18 15:00:46 CDT 2008

> > I'm moderately sure that the paper tape I used back when I had a PDP-8
> > was not symmetric in the way needed here - the line of feed/timing
> > holes was not on the centreline of the tape.
> You are remembering correctly - they are not.
> *But*, you could read the tape one way, flip it _and_ read it backwards.
> Syncing up the two passes is just an exercise for the student ;-)

What possible good can that do? The same tracks line up with the same 
phototransistors, so if one of the latter is dead you lose the same track 
both times.

> Personally, my PC04 is the primary load device for one of my PDP-8/Ls.
> I'd be hurting if I lost a phototransistor - the SMT idea sounds handy.
> What I'm more worried about is a spare bulb - It's a "festoon" bulb
> (the kind commonly used for older automobile dome lights - it looks
> like a large AGC-type glass fuse, with an axial filament), but trying
> to cross it with a modern one from Osram or others has drawn a blank
> for me.   Has anyone found a modern substitute?

Is it particularly critical? I can't even remember what the voltage is 
supposed to be, but assuming you can find something of the right voltage 
and about the same wattage it should work.

Now, finding replacement bulbs for an HP2748 is another matter (that 
reader has an individual 'grain of wheat' bulb for each track, all 10 (8 
data tracks, feed track, reference lamp) in series across a 45V supply.


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