[Heathkit] question on keying a SB-221

[rbig]

Thanks, Bill.   Great answer.    

I appreciate the response.   

It seems that using the Harbach mod will make any rig key it OK



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).