I've used 10M resistors, not often, mind you, but
I have. I think
I think the larged 'normal looking' resistor with coloured bands that
I've seen/used was 22M, Maybe 56N
I've seen 100M but had no cause to employ it.
I've certainly used 1G resistors, but for measuring instruemtns, not in
classic computers (or consumer electronics).
=A0 It is very funny to see a resistor encased on
a glass tube :oD Thes=
e are
things I never imagined seeing :oD
I've seen numerous precision resistors over 1M in glass, though they
were used in physics experiments, not commercial or consumer
electronic devices.
Thetes' one place you might well find high-value resistors, and that's in
the EHT circuits for CRTs. An EHT voltmeer can be nothing more than a
microammeter and a high-value resistor in series, in fact the Heathkit
one that I have (the only Heathkit I ever built...) is just a 50uA
moving-colil meter and an 800M resistor (it measures up to 40kV, of
course). That reissotr is a glass tube about 6" long, in the barrel of
the probe. It has femae threads at each end, the probe spike screws into
one of them, the other goes onto an adapter that's wired ot the meter.
Some of the better monitors (like my Barco and the one on my HP9836CU)
have regulated EHT supplies. THis typically involves a portential divider
conencted across the (25kV) supply to the CRT anode, with the tap (at a
nice low voltae, around 12V, say) goign to the error amplifier that
controles the EHT supply. Since the currents inolved are necessrily low,
the 'top' reisistor is a high-value thing. It also has to be
well-insulated since it's dropping nearly 25kV. It doesn't look like a
reissotr, it's a potted modlue with the EHT cable going in one side and a
normnal wire coming out the other going to the rest of the cirucity.. My
scheamtic for the HP monitor I mentioend says I measured it (it wasn't
marked) as 200M.
-tony
