Bob Morris K2RK wrote:
> I assume the diode is the standard spike protection, provide
> outboard.
That's what I was curious about. It is impossible to add eternal spike
protection with a diode, unless the diode is a zener or a biased diode
clamp.
The reason is this...
The back pulse coming out of the amplifier, as the relay line is opened,
is the same polarity as the initial keying voltage. If you have a plus
12 volt line, the backpulse will be a positive voltage of many volts.
Assuming a 12 volt line, the only way to externally clamp the backpulse
voltage is to use a conventional diode with its' cathode tied to a
positive twelve volt (very stiff) source and anode to the relay line
(clamping the relay line positive voltage spike at 12 volts), or to use
a 12 or 14 volt zener clamp to ground.
A cathode to keying line NON-zener diode, or a series diode, does
nothing.
> ps... The 3-500 AC wiring...in the ARRL Handbook. I couldn't even
> figure out what they were saying to comment on it...
>
> Quote---- 1995 ARRL Handbook - 1995, page 13.36, fig 13.37
>
> "Chassis ground is not equivalent to the ac-line ground.
> The ac neutral wire is connected to chassis ground, so the chassis
> must be isolated from the equipment cabinet, which must be connected
> to the ac ground conductor"
They obviously were aware the 3-500 amp was unsafe because of the
warning, but how do you isolate the chassis of the amplifier from the
grounded cabinet?? That seems even more unsafe! Can you imagine
completely isolating the SO-239's for ac voltage while not upsetting RF
grounding??
Seems like a lot of work when proper primary wiring would cure the
problem.
>Not just ac but there's 3 0r 4 kv going to this box....
>
> Get an extra copy of the Handbook, so your widow can give it to
> her lawyer....
There are also two 2000 volt plus supplies that have the neagative leads
improperly clamped (only via a reistor), and have no chassis safety
grounds. If either supply would develop a primary to secondary
transformer short, or if a lead should break or a high voltage fault
occur, the chassis or negative leads could "fly up" to full high
voltage.
Not a very safe thing for the hamshack.
73 Tom
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