26 Apr
2005
26 Apr
'05
7:19 p.m.
Subject: Re: small valves and RE: OT
From: ard at p850ug1.demon.co.uk (Tony Duell)
Date: Wed, 27 Apr 2005 00:49:28 +0100 (BST)
To: cctalk at classiccmp.org
However, there are plenty of other people reading this list, who might
come across similar sets. I would hope they might now realise that the
chassis could be live.
Ah, threin lies the reason. However good point.
People here play with power in the form of higher voltages, also in
the form of high energy. Some of those computer supplies designed
to pump out dozens to sometimes hundres of amps of power posess
the capability to melt off a ring (and the encircled finger), watch
or cause a splatter of melted metal in the eye. Trust me, I have
been been to 1500volts and back due to fools around me and their
pointing fingers. I've also seen what an 80amp regulated power
supply can do to a 1/4" shank screw driver. That little ditty
vaporized in a nice UV rich arc. Had me seeing spots for a
week(welders burn). Oh and the guy fixing it was quick state he
had unplugged it. So yes, a reminder for those listening is far
from out of order.
[1] The presence of a mains transformer in a valve
radio does not imply an
isolated chassis!. It was not unhead-of for the transformer to be to
supply the heaters only, with the HT coming by half-wave rectifying the
mains, thus giving a live chassis. Some UK sets even had the heaters in
series, runn from the mains via an autotransformer...
Yep, that too!
I might add that something "grounded" can be more unsafe until your
sure there is NO POTENTIAL differences. I got dinged in NYC one
fine day due to a mere 65vac differential in grounds between the
12th and 14th floor. And they couldn't understand why the RS232
drivers were being fried all over the place. Seems equipment
ground wasn't.
Electrons are our friends, they have a dark side too. Always play
nice and use proper technique. Failure to do so really can take
the fun out of it.
Allison