[Amps] Step Start on a 3KA Amp

[Phil Clements]

> The first 1 to 5 cycles is the worst part of the surge, but from tests
> that was run by a ham on this mailer, the transformer didn't settle down
> until 30 to 40 cycles. This was captured on a storage scope and I have the
> results here somewhere saved as a jpeg photo. Anyhow, a 1/2 second delay
> is about all that's needed on the step start. I'd say they used this
> heater cone over its greater power rating than would be a 25 watt or so
> resistor. 

The reason for the cone heater instead of a 25-50 watt resistor is that this
is a "manual" step-start circuit on the Henrys. It only has three parts; a
cone heater, a switch, and the operator's hand. As the switch is rotated
from off to on, it allows the mains current to flow through the cone heater,
step-starting the power supply. Since it is possible for the operator to
screw up and leave the switch in a position that the cone heater is still in
the circuit, it required a robust resistance in order to stand the
continuous duty in a situation like this. Some folks who don't read the
Henry manual think this is a "hi-lo" or "SSB-CW" power switch instead of a
step-start, and try to operate the amp in the intermediate switch position.
Even the robust cone heater has its limitations (300 watts-1000 watts,
depending on the model) and will fail open after this abuse goes on for a
period of time. A savvy operator, when turning on the amp, will pause in the
intermediate switch position until the HV meter gets up to 3/4 of its final
normal value. This will usually take less than one second. At any rate, when
the HV meter has come to a stop during turn-on, the "step-start" function is
complete, and the switch should be moved to the "on" position immediately to
prevent over-heating of the coil on the cone heater.

(((73)))
Phil Clements, K5PC