light bulbs for DEC front panels

From: CLASSICCMP_at_trailing-edge.com <(CLASSICCMP_at_trailing-edge.com)>
Date: Tue Apr 18 20:20:11 2000

>Does anyone have information on light bulbs for DEC front panels
>circa 1968, in particular from a KA10 panel?
>I've been told that there were also plug-compatible LED lamps in red and
>green. These obviously must have contained a series current limiting
>resistor. Any info?

If they're anything like the -8 front panels, there is also a "warming"
current through the bulb. The aftermarket LED "upgrades" either had you
snip the resistors that kept the prelight current flowing on the front
panel drivers, or (more classy) they had
divider networks in addition to current limiting to make sure the warming
current didn't appreciably light the LED.

It was about three years ago I posted an analysis of the divider method
to alt.sys.pdp8. I'd be glad to dredge up those calculations here if there
is any interest. The divider method is a little more complicated to
solder up, but it's easier to go back to real light bulbs if/when you decide
to go back to the "completely original" look.

Tim.
Received on Tue Apr 18 2000 - 20:20:11 BST