[Amps] Step Start circuit - needed or not?

[herzog@frontiernet.net@frontiernet.net]

Replying to:Subject: Re: [Amps] [HeathKit_HFAmps] Step Start circuit -
needed or not?
I say NEEDED when in doubt.
I designed a ten KW amp, at my day job.
I didn't know why Collins used a step start in their 208-U10 amp.
We were competing on money bid, so I left it out.
After 150 Military transmitters, We got around to discovering the why;
so subsequent commercial transmitters had the step start added.

The inrush current varies. depending upon the magnet memory of the core
when it was shut off, and the voltage of the sine wave upon
contactor/relay closure. 
 A par 30 amp inrush could be 900 amps every hundredth turn-on.
This manifested itself in several fronts:

Fuses in the mains quit.  
misc-unexplained HV rectifier diode failures.
AND MOST IMPORTANTLY: welding of a hv contactor/relay, causing
intermittent hv to come on with vibrations closing the other side of the
stuck-on relay; fortunately caught before someone had to die!!!!

A step-start relay with fusible resistors, instead of the huge relays
collinbs used, saved all these BG problems, and I damn near learned too
late about the why.  Wil Herzog K2LB
=========================RE:
To: <HeathKit_HFAmps at yahoogroups.com>,  <amps at contesting.com>

It is not necessary but if it makes you feel good then do it. You will
s also help the economy.........

Many ignore the fact that the power and filament transformers or
windings when combined, offer more than sufficient inrush protection.
Instead they ignore those items in the calculations.

The SB-1000 requirement was established years ago when the designer
stated that inrush was not necessary and only included in later
Ameritron amps to satisfy the Nervous Nellies that believe every thing
that is published in ham rags by uninformed people. The SB-1000 is an
AL-80 clone for the most part and was sold to Heath by Ameritron.

Ameritron also offers parts support even today.

Carl
KM1H