[Heathkit] question on keying a SB221

[William Houghton]

TS-430S: no, not directly.

FT-100EE, yes.

Here is the reason. The Heathkit amplifiers, like many of their era, used a 
relay with a coil voltage of about 120VDC.  Unkeyed, the relay input of the amp 
will sit at this 120V. To key the amp you switch this voltage to ground. 


Chances are that your nice solid state TS-430 is not designed to switch 120V to 
ground.

In the old days, rigs typically used a mechanical relay to key amplifiers. In 
some radios one of the contacts was connected to chassis ground. In some rigs, 
both contacts "floated". Either of these relay methods can be used with the 
SB-2xx amps. The FT-101 series has a relay with one contact connected to the 
chassis if I recall correctly.

A common method to interface the sold state rigs to these amplifiers is to 
install an interface circuit so that your radio sees a low voltage low current 
keying signal and the interface switches the 120V signal. The interface can be 
as simple as installing a low voltage relay powered with a small transformer. 
The Harbach SoftKey circuit performs this interface (I don't know if theirs uses 
a relay). 


73,

Bill



________________________________
From: rbig <rbig at cox.net>
To: heathkit at mailman.qth.net
Sent: Wed, April 17, 2013 9:00:56 PM
Subject: [Heathkit] question on keying a SB221

I have a Kenwood TS-430S, and a Yaesu FT-101ee.

Can either or both of those key my SB221 OK?
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