[Heathkit] sure will appreciate help on getting straightened out on SB-221

[William Houghton]

Softkey - the Heathkit SB-200, SB-201, SB-220, and SB-221 all used a 120VDC 
relay to key the amplifier. This meant that YOUR transmitter needed to be able 
to switch a 120VDC signal to ground. This usually was not a problem with vintage 
tube rigs. Most modern solid state rigs cannot withstand the 120VDC on their 
amplifier keying line. You need a circuit which will interface the typically low 
voltage keying signal from a modern rig to the 120VDC keying input of the 
amplifier. The SoftKey circuit installs inside the amplifier and converts it 
into a low voltage keying input that should be compatible with just about any 
solid state rig. Ameritron and others have external boxes that perform the same 
function.

You could also drive a low voltage low current relay with a solid state rig and 
have that relay's contacts drive the keying input of the amplifier. This does 
add more relay switching time 


SoftStart - When you first apply power to the high voltage transformer of your 
amp, and its filter caps are discharged, the transformer sees close to a dead 
short on the secondary. This results in a very high current in the secondary and 
even higher current in the primary. A softstart circuit typically has a resistor 
in series with the primary of the transformer to limit the current. Typically 
there is also a relay who's contacts are in parallel with the resistor . After a 
short period of time, the relay closes shorting out the resistor. So when you 
first power on the HV in your amp, the primary current is limited by the 
resistor until the caps have had time to partially charge up. Then the resistor 
is shorted out allowing full AC line voltage to appear across the primary.

RY-220 is simply a replacement relay for the original Heathkit relay. You only 
need this if your orignal Heathkit relay is defective.

Does that help to clear things up?

73,

Bill



________________________________
From: "rbig at cox.net" <rbig at cox.net>
To: heathkit at mailman.qth.net
Sent: Sun, February 17, 2013 7:12:08 AM
Subject: [Heathkit] sure will appreciate help on getting straightened out on 
SB-221

The guy that sold it to me said I needed a buffer relay.  What he says may be 
protection for my tranceiver.  This guy has an article on what I think I may 
need: 


http://www.wy6k.com/homebrew_stuff/power_amp_driver.htm

There should be some finished products available for this.  Does anyone know of 
any?  I'd really rather buy a finished product that to try and build one.  


Harbach has a Soft-key mod they sell (SK-220).  I'm not sure if this is like the 
buffer relay above, or not.    I'll get it and put it in.

They also have a Soft-Start mod, which I'll get and put in.

I think this one is not like the buffer relay.  I think this is the relay in 
cabinet.  It's called a Harbach Relay Replacment (RY-220.

Sure will appreciate getting straightened out on all these things.    

Also, does the SB-221 have compatability between ALC from TS-430S, FT-101zd, 
FT-101ee?  Will those be able to have ALC on this amp?  

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