AC/DC radio precautions, was Old Radios

From: Marty <>
Date: Mon Dec 28 15:54:31 1998

 Chris is quite right. Sorry, the light bulb rig was a bad idea (I have
 never used it but it was mentioned to me once upon a time) and I agree
 the isolation transformer is definitely the ONLY way to go. Regarding
 trusting a spec sheet or schematic, I wouldn't. Many sets I've come
 across have been modified, often in unconventional ways.

______________________________ Reply Separator
Subject: Re: AC/DC radio precautions, was Old Radios
Author: at internet
Date: 12/28/98 3:31 PM

 At 12:15 12/28/98 -0500, you wrote:
>______________________________ Reply Separator
>Subject: Re: Old Radios
>Author: at internet
>Date: 12/23/98 6:44 PM
> >
> > Come now comrade Griffiths, an old radio never hurt anyone.
> >>>What, not even if you touch the chassis of an AA5 with wet hands?
> I stand corrected. This is a good time to mention to our list members
> that if they find an old tube radio, especially an AC/DC set (you can
> tell this by the absence of a power transformer and a tube complement
> which will equal 120 volts for total filament voltage, some even have
> often having the 120 hot wire soldered to the chassis. If you touch
> the chassis on one of these sets wired with the hot to chassis, then
> ground yourself, you'll electrocute yourself. Always use one hand only
> so you don't provide a path for the current (likewise be certain you
> have insulated shoes, not providing a current path anywhere on your
> body). If you need to work on one of these sets, use an isolation
 These points are valid . . .
> transformer or wire a light bulb between the set and house current
> (the light bulb filiment should open before you fry, thus breaking the
> circuit).
 Hold on there! An isolation transformer is the *only* way to go to
 provide isolation from the line for a transformerless radio or TV.
 The light bulb will NOT open (like a fuse, as the above statement infers)
 but will simply pass current up to at least the wattage rating of the
 filament. (100W bulb = approx 0.9 Amperes _at_ 115V.) A few microamperes could
 be enough to kill a person under many conditions at this voltage.
 The concern for inexperienced folks handling a bare chassis of a
 transformerless set is nonetheless well placed and the part about the
 chassis being hot (115VAC in North Amer. or 230VAC in most of the other
 parts of Earth) is particularly important to be aware of. A chassis could
 be hot even if the line cord is correctly plugged into the wall receptacle.
 This is because a commonly used signal bypass capacitor from the hot side
 to chassis often is quite leaky (simply, it has relatively low DC
 resistance) or even shorted from age. I've been hit too many times while
 handling these sets over the past 33 or 34 years.
 As with any of us troubleshooting computer power supplies while the power
 is on, *always* stuff one hand into your pocket while probing around in the
 Enough of this off topic radio stuff --although I had to post this to
 correct a seriously incorrect piece of advice given above. On topic part
 could be to note that using an isolation transformer while poking around in
 a computer's switching power supply could make accidentally touching a few
 parts in the line-side of the PSU somewhat safer.
 Just being careful and focusing on where one's hands are at absolutely all
 times is the safer way to go while having to work on live high voltage
 Regards, Chris
 -- --
 Christian Fandt, Electronic/Electrical Historian
 Jamestown, NY USA
 Member of Antique Wireless Association
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 Subject: Re: AC/DC radio precautions, was Old Radios
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