Soft Key for SB-200

[Robert Norgard]

The soft key circuit (for all practical purposes) replaces the
125 DC volts found on the key circuit on the back panel of the
SB-200 with about 6 volts or less.   With the soft key, keying
current is only a few milliamps.

I think that the stock keying circuit was only meant to be
connected to a dry contact in the form of a relay located inside
the driving transceiver.

With the soft key circuit, the new low voltage/low current
requirement means that it may now, in addition, be driven with
an open collector circuit, as some SS rigs now use.

On mine, I use a circuit very similar to the Harbach version,
but powered internally by a separate transformer power supply,
instead of the filament winding on the stock transformer.  I've
heard no complaints about the Harbach mod.  A friend of mine put
one in down in W4 land, and he still drives it with an SB-102.

Also, If driving with a SS rig, you probably or obviously can't
hook up the ALC.  Don't worry about it.  Just keep the drive at
no more than 60 watts.  Mine drives to full output before I get
to 60 watts.  Most of the time it's between 50 - 60 watts, and
this is with weak tubes.

73,

Bob - KL7FM

PS I have about a dozen photos or so that I will be putting up
on my website soon that detail the inside of my SB-200.  All I
need is a little time to work on the page.

Sponsored by the City of Tempe 

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