HP 2748B bulb replacement

[Tony Duell]

> 
> 
> > My apologies for not telling the whole story.
> :-)
> 
> 
> > ...so I bought 20 of them as a life-time
> > supply.
> Hm, how old are you?!?

They seem to be somewhat under-voltaged in the 2748 (they don't glow that 
'white') so they should last a long time.
 
> > I haven't finished my microcontroller interface to the 2748B yet but the
> > tests in the service manual indicate that the replaced bulbs are doing
> > the job nicely.
> That belongs to a minicontroller instead a microcontroller....

Mine (a 2748A) came off an HP2100A system, but I now use it with an HP9830
'calculator'. I found the right interface on E-bay -- it's a 11202 8-bit 
parallel interface with the right connector on the end of the cable. 
Needless to say it works fine.

> You can just hook it up to your pc. I have a printer port "paper tape" 

One minor problem is that the 2748A doesn't use TTL levels. It's a minor
problem because on the -B you have a 'TTL clamp' jumper on the interface 
connector, if you fit that then you gry 5V outputs. The -A model doens't 
have this., but interesting the output circuity will give TTL levels if 
connected ot a TTL input terminated to +5V and ground by the appropirate 
pair of reuistors (which just happen to be the ones used in the 11202)

-tony