http://www.ipernity.com/doc/777361/45315684



Guys and gals, I just read in another group how one of its member got thrown across the room and nearly killed simply by touching a damaged resistor in an amp he was working on.



So, some points:

A good many radios and other equipment discussed here are hot-chassis devices. Meaning that the chassis is hot (and anything metal touching or connected to the chassis) 100% of the time the radio is on, and (at least) 50% of the time the radio is off,
but plugged in.

Whereas the B+ in a typical AA5 is only about 90 - 120 V, and not the 500 VDC experienced by the gentleman noted above, 120 VAC can still be plenty lethal, and if anyone has any sort of heart condition, epilepsy, or similar, even more so.

So, if anyone here ever intends to work on these radios at any level other than cleaning and playing, please invest in those basic tools that enhance workplace safety, and help to preserve life. Keep in mind that NOTHING is idiot-proof, but at least one
may engage in basic precautions.

The link above is to a metered Iso-Variac. I keep two. One permanently affixed to the bench, the other in the travel kit that follows me around to meets and clinics. NOTHING gets tested anywhere, unless through one of the above.

How much is your life worth?

Peter Wieck
Melrose Park, PA

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On 8/15/19 7:27 AM, Peter Wieck wrote:

http://www.ipernity.com/doc/777361/45315684

Guys and gals, I just read in another group how one of its member got thrown across the room and nearly killed simply by touching a damaged resistor in an amp he was working on.

Peter, as always you provide some good insight. I have several old
vacuum tube AM radios that have electrically hot chassis, among them a Hallicrafters S-38E (the metal cabinet is insulated from the inner hot
chassis) and a 4-tube Sears Silvertone (model 2 chassis 132.878).
What's interesting about the Sears radio is that it doesn't have the
usual internal loop antenna - instead there's a length of wire that
needs to be extended and that wire, while cloth covered, is hot wrt AC
ground. Both of these radios have a non-polarized plug attached, and
whether the chassis is hot or not depends on which way the plug is
inserted into the wall receptacle.

What do you think about replacing the old plug/cords with a polarized
plug end so that the chassis remains "cool" (either in direct or
indirect contact with the AC outlet's neutral rather than hot wire)?
Thanks for your time and comment. Sincerely,


--
J. B. Wood e-mail: arl_123234@hotmail.com

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Good point! I am a great believer in polarized plugs! And my wife will tell anyone that asks how I ran around our "new" house 11 years ago with one of these:

https://cdn2.bigcommerce.com/server5300/3ob78/products/1059/images/2827/012__46380.1408725829.320.320.png?c=2

and a roll of blue masking tape. Of seventy (70) receptacles, six (6) had the hot and neutral reversed. Note that standard two and three-prong receptacles in the USA have been polarized since the 1920s, at least.

Yes, to the extent possible, make sure that the hot side goes through the switch.

Peter Wieck
Melrose Park, PA

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