19 Dec
1998
19 Dec
'98
1:46 p.m.
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Sunday, 20 December 1998 14:56
Subject: Re: Electrical knowledge, was Another ~1960 computer kit
Incidentally, in the days of valves, you could light a
neon mains tester
by holding it near (not touching) the line output valve (sweep tube?). A
very quick test for EHT problems.
A screwdriver (insulated handle!) blade touched to the top cap of the
1S2 would produce a healthy arc when held somewhere near chassis
if the line/eht stage was running. This practice did not survive the
transition
to solid state devices that disliked the spikes etc it could cause!
> Another example, it surprises me how many
"electrical" people do not
> understand, for example, what happens when one wires speakers in series
or
> parallel.
Several non-electrically minded customers of mine now have 1st hand
knowledge
of the effects of this. 1 particular Guy had no less than 8 speakers wired
in a series/parallel MESS
(whether a speaker was series or parallel was determined by it's physical
location in relation
to the audio leads he had running all over the house) Actual impedance was
around 1 ohm on
the left channel and about 2 on the right. Result: 1 very dead STK chip
output amp.
Amazingly, it actually worked for about an hour before expiring.
Seems he had done something similar in the past (old fella) with valve based
stuff, and aside
from a little(?) distortion it worked. I guess that
proves that valves
have their advantages.
I suspect the Speaker Transformer on the valve amp could have been used to
boil water though.
Cheers
Geoff Roberts
Computer Room Internet Cafe
Port Pirie
South Australia.
netcafe(a)pirie.mtx.net.au