WTB: DEC PC04 Paper Tape Reader/Punch

Vincent Slyngstad vrs at msn.com
Mon Aug 18 12:55:14 CDT 2008

From: "Ethan Dicks" 
> *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 ;-)

Alas, that wouldn't help with the bad phototransistor.

> 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.

It sounds interesting to me too.  Are there detailed specs for the 
phototransistor array, or would I have to take my PC04 apart and 
measure everything?

Some PC04 seem to need 10 phototransistors, while others leave the 
tenth phototransistor unconnected.  I haven't looked at how hard it 
would be to convert the former to the latter.  I suspect the sprocket 
sensor could be made to sense the out-of-tape condition, since the 
out-of-tape detection is based on requiring a pulse train.

> 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?

Well, there's this sort of thing:
The tricky part for these seems to be getting ones that will work well 
on 5V.

Isn't it basically exactly an old-school 6V automotive dome light?
I wasn't able to find a part number for the original, so I don't know 
the original dimensions, either.  There seem to be at least a couple 
of common lengths.

Curious that the documentation doesn't suggest stocking a replacement, 
or even tell you what part to use.

If it's DEC part number 12-04903, then that's available here:


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