15 Jun
2014
15 Jun
'14
1:14 p.m.
On 15/06/14 12:43 PM, Henk wrote:
-----Oorspronkelijk bericht----- From: Toby Thain
Sent: Sunday, June 15, 2014 5:49 PM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: DG Nova 3 Bulb Number?
On 14/06/14 12:21 PM, Mark J. Blair wrote:
That would be snarfusmaximus who I quoted above, I think.
Do any of y'all know the bulb number for the
fragile little
wire-leaded bulbs used in the Data General Nova's switch console? I
have at least one burned out, and a couple have snapped off. I measure
about 15V across the bulbs on my machine, but I don't know yet whether
that's the correct voltage, nor do I know the nominal voltage, current
or brightness ratings of the correct bulbs.
Picture:
https://twitter.com/nf6x/status/477846674543362048/photo/1
Via email, snarfusmaximus writes, "I replaced mine with yellow LEDs with
a series resistor."
--Toby
I do not have the schematic of the NOVA 3 console, but I seem to
remember that the bulbs have a series-resistor to make some current
flow through each bulb continuously. The current is low, so you do
not see the filament glow. But when the full voltage (whatever that is)
is applied, the bulbs lights up quicker because it is already "warmed".
IIRC, this is also used in PDP-11/45 (and /70?) with bulbs, before the
bulbs got replaced by LEDs (and the series-resistor was also removed).
So, when you substitute the bulbs wth LEDs, you can remove that
series-resistor. There is a website of a chap in Australia that did this
and has a description of his "actions".
Although LEDs are certainly a lot easier and have longer lifetime,
they are not a 100% replacement. Bulbs have a color temperature that
is dependent on the current flow. Thus on a running computer, some
lights seems more orange than others due to the duty cycle of the
applied signal.
Doesn't the duty cycle modulate the brightness of LEDs?
--Toby
- Henk