I heartily second Ward's words and Jim's advice.
Every one of the legal limit tube amps that I built incorporated
interlocks. The first amp used a free TV station's timed out 4-1000A.
It was built per the 17th ed. of William I. Orr, W6SAI's /Radio
Handbook/, page 682.
My dad became a SK at the age of 64 when he put the cover back on his
amp, right after shutting it down. Arc marks indicated that the cover
contacted the top of the plate choke. Burn marks on dad indicated that
the current path through him was from both hands which were holding the
cover to his abdomen which was touching his mike. Although voltage was
bleeding off, there was sufficient energy in the voltage doubler power
supply caps to cause muscle reaction that sent him backwards about 6
feet and kill him.
When working around exposed HV a second opportunity to make a mistake is
improbable.
73, Jim, K7AJM
On 1/7/2017 9:14 AM, Ward Silver wrote:
> Excellent advice, Jim.
Hear, hear!
And another good piece of advice is to make sure you have an ac safety
ground connection on every metal enclosure. With 12 Vdc being the
normal power supply voltage these days, we can get away with practices
that would really be hazardous for tube-based gear.
> A 50 uF capacitor charged to 4000 V holds a potentially deadly 400
Joules of energy
In the defibrillator business of a few years ago, this was known as
the "rescue shock" of last resort. This amount of energy can lift a
200-pound person 1.5 feet. When leveraged by muscle-and-bone, much
damage can be done.
73, Ward N0AX
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