I have an old 'Snap-On' distributor testing machine (mid 60's) model
MT-605 that has 2 small neon bulbs in it.
These bulbs are about 3" long by 1/4" dia, one red, one blue and has
the electrical connection as a pin at each end.
The problem I have is that they are both burned out and 'Snap-on' no
longer has parts for the machine.
From a parts list I have, I find they where made by a company called
Amglo Corp. Rosemont Il. but that company is also gone.
From a wiring diagram it looks like they get there power from a
transformer which is marked 675V 20MA so assume this the feed voltage
and amp draw to the bulbs. The primary to the machine itself is
120Volt.
What I am looking for is a bulb that will work in this unit like the
original bulb in size or a similar bulb I can adapt to make work. The
function of these bulbs is to provide a back light that can be seen
through a slot in a revolving panel.
Thanks
Mike
dailuracer@yahoo.com

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Clarification of Question by snapon-ga on 25 Oct 2004 15:34 PDT

An Update,
I have checked the voltage at the bulb socket and find one measure
14.4 volts a/c and the other between 26.8 & 33.4 volts a/c, not sure
which color bulb is which voltage.
 In looking at the wiring diagram again I do see something in the line
which may reduce the voltage.
 I have scanned the wiring diagram and the bulb so can e-mail them if
it would help.
Thanks
Mike

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Clarification of Question by snapon-ga on 25 Oct 2004 15:35 PDT

Hi,
Thanks for your help.
I have looked at the wiring diagram again and it still looks like the
bulbs are in a circuit that comes off the transformer that list them
at 675 Volt, I did notice that one of the bulbs, the 'blue one' is
listed as 'neon mercury tube'.
I will try to get a a voltage reading off one of the bulb circuits and
post it later. I have scanned the wiring diagram I have but not sure
if I can ad it to this posting but could send it to an e-mail or fax
address if it would help.
The bulb is a glass tube 2.5" long by .25" dia. there is a wire pin
that comes out of each end, about .25" long to give an overall length
of 3". each wire pin goes into the bulb and goes into a little netal
barrel shape thing that is about 1/16" dia. by 1/4" long. the distance
between the barrels is 1.5", there is no element in the bulb so assume
it is the neon gas that carries the voltage between them.
Thanks
Mike Leicester
dailuracer@yahoo.com

If these are definitely neon types (though of course blue filtered
neon will emit nothing) the 675 volts is tad high. Cold discharge
tubes exhibit very low resistance when ignited and must be driven from
a current limiter, usually a resistor of tens of k ohms. If indeed
these are discharge tubes supplied from 675 volts, you could simply
run several standard ones in series -- with the obligatory resistor of
course. I suspect however they are more unusual than that so are there
any more details you can supply, like measuring the terminal voltage
and describing the bulbs in more detail. Can you see the remnants of a
filament?

Best

Have fired an email to you for contact. Surprised Goog left it on --
they are quite protective in an avuncular sort of way.

It would be wonderful of Goog if they would act as intermediaries for
email addressed for diagrams etc. Please .......

Anyway, in meantime, this is a remarkably peculiar bulb. Your
description is that of a cold cathode discharge tube -- or more
normally a CCFL, cold cathode fluorescent lamp. You could check out
the technology with a ?CCFL? search. However, what I don?t understand
is how it is blue because mercury emits in the UV and a phosphor is
required to make blue. Nice picture on :-

http://www.tridentdisplays.co.uk/home.shtml/?/articles/tft_backlight.shtml

Found Amglo, but no useful info. You could try mailing them -- good luck......

http://www.amglo.com/

You could check out links on this page too :-

http://www.1800miti.com/links/manufacturing/group_d/elec-bulb.html

Though discharge lamps are often generically called ?neon?, it?s
likely a mix of neon and mercury. The neon is needed to initiate the
discharge. But the fact that you can see the electrodes means that
there isn?t a phosphor coating, unless the coating doesn?t extend to
the ends? I?m also assuming that there isn?t a blue coating on the
bulb?

As I said, current must be limited, usually by a resistor but if it?s
an AC supply it could use a large inductor -- but it would need to be
massive at that voltage and small current. It is also possible to do
it with a poorly couple transformer but a resistor is so much cheaper.
Be nice to see the diagram.

Suppose blue was used ?cos it looked sexy. But if you can lose the
blue, as I said a few smaller neons in series should suffice. If there
is a low voltage supply, blue LEDs could be hooked up. I can advise on
that too.

Best