[CQ-Contest] SB-220 Switching help

[Tom Rauch]

> Can any of you tell me how much current the SB-220 t/r relay draws ?
> 
> I know it's a 120v device, but need to know it's current draw.


It's been a few years since I designed for Heath, but as I recall that 
relay system sourced about 20 mA when pulled low.  The problem 
is the voltage is high, and that voltage charges bypass capacitors, 
because of that, the pulse current can be quite high. In the 
neighborhood of a half ampere or more!  Upon release, the back 
EMF can be a few hundred volts or more.

It was designed when most rigs had 5 ampere or larger 120 volt 
relay contacts to switch external PA's! 

I'd buffer the relay line with an isolation device before connecting it 
to any modern radio!
73, Tom W8JI
W8JI at contesting.com 


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