[Amps] Adding a soft start circuit in my Henry 5K Classic

[Alan R. Downing]

Good afternoon all.  Alan, N7MIT here.

My Henry 5K Classic did not have a soft start circuit in it when it left the
factory, unlike my 8K Ultra which did.  I got sick and tired of being nickel
and dimed to death by component failures caused by the tremendous inrush
current when I turned the amp on.  The amp damn near jumped off of the floor
when I flipped on the 40 amp two pole breaker.  I finally added a soft start
circuit and all of the problems went away.  I placed a 100 watt 10 ohm
Ohmite wirewound resistor in series with the primary circuit of the
transformer.  To short out the resistor after the oil filled cap charges up,
I used a Crydom D2475 electronic contactor.  The D2475 uses zero-crossing
circuitry to limit current when the resistor is initially shorted out.  Now
when I power up the amp, the only thing I hear is the blower spooling up.
There are no thuds, bumps, or any other loud bangs when the amp is
activated.  I have not had a single component failure in the supply since
adding the soft start either.  It works great now, and cost me less than
$100 to straighten out.


Best 73
Alan - N7MIT

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