It is the ARB-704.  I have one between my FT-950 and the old Yaesu FL-2500
sweep-tube amplifier I use.  Older amplifiers like this were keyed by a
relay in the transmitter or transceiver that drove them.  Thus, if the coil
drew 100 milliamps or more, it was no big deal.  Also, if the voltage was 50
or 60 volts, the transceiver's relay could take it.

Modern transceivers have a transistor at the keying connector, and expect
lower voltages and currents to be keyed, as found in modern linear
amplifiers.  I don't think this relay buffer contains additional relays, but
contains some more beefy transistors that can take what the linear produces.

In my case, if I drive my linear above a certain power level, the relay
begins to trip out intermittently.  I haven't identified the cause yet.  It
could be ground loops, RF on the keying line, or something else.

Lloyd Rasmussen, Kensington, Maryland
Home:  http://lras.home.sprynet.com
Work:  http://www.loc.gov/nls
 
> -----Original Message-----
> From: For blind ham radio operators [mailto:[log in to unmask]]
> On Behalf Of Phil Scovell
> Sent: Sunday, May 02, 2010 12:36 AM
> To: [log in to unmask]
> Subject: ARB 740
> 
> Are any of you Icom users, along with solid state amps, using the MFJ ARB
> 704 between the transceiver and amp for voltage protection and the like?
> 
> Phil.
> [log in to unmask]
> WWW.RedWhiteAndBlue.ORG