Gents,
In building step-start units to ease the trauma of powering up
various amplifiers a number of issues were addressed:
The filter capacitors present an almost dead short when
first being charged. (Anode Supply). In the latest case,
there's 50uF at 5KV WVDC needing to be charged,
and I was worried that my rectifier bank would be
unduly stressed if I didn't limit the inrush current.
As an example, the Alpha 77 series with dual voltage
composite transformer uses two resistors, one on each leg,
shorted by a 24 volt contactor, K2, after stepping. These
resistors were protected by a 3AG type fuse in series with them.
Just like the poster who talked about the chicken with no legs
in the oven, when designing the stepper for the 3 ampere
outboard supply mentioned above, a resistor was inserted
in series with each leg of the new xfmr by a 40 amp relay driven
by a Crouzet timer. Unlike the Alpha that had only one fuse
in series, this supply has a fuse in series with both legs. My
thinking was to reduce the total trauma, even though the
electrical ramifications only impose one resistance.
However, is it wise or necessary to limit the step-start to
one second or less? Would not the oil filled caps need
a few seconds to charge up?
What damage would occur if the step-start period were too long,
considering that the stepping timer and drive were run by a full
voltage supply and didn't chatter?
Lastly, when switching the output of the transformer from 2.5KV to 4KV,
well after stepping, (going from "CW" to "SSB"), the xfmr still makes an
audible thump. Is there any protection needed at that point?
Respectfully,
Hal/W4HBM
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