[AMPS] Faster Amp Relay Switching

[Michael C. Joens]

In follow-up to a recent posting about a circuit to accelerate relay 
switching, here's another method. It works great with my Icom IC-756 and 
Drake L-4B.

Instead of using the relay output from the rig, I use the PTT line in the 
accessory port. The IC-756, like most modern Icom rigs, actually has two 
such ports, and the PTT pin is the same on both. This line is an I/O line, 
it can be used either as an input (for footswitch or computer keying) or as 
an output (goes low on transmit) or both. Using this line to trigger the 
amp relay eliminates the delay the rig's reed relay would introduce 
(several milliseconds).

To interface between the rig's PTT line and the amplifier, I use 2 
transistors (2N2222 and 2N3055), 3 resistors and 2 diodes. Power comes from 
the rig (available on the same accessory port). For an SASE I'll send a 
copy of the schematic. The circuit works well with the Drake L-4B, which 
uses 30V to power the relay circuit. It should work ok for any linear whose 
relay voltage is between 12V and 50V With some modification, it should also 
work for an SB-220's 120V line. I'd probably use a FET instead of the 3055, 
though.

Switching the L-4B with this circuit instead of the normal amp output relay 
has completely eliminated hotswitching in RTTY and CW semi-break-in. It 
does not allow QSK, however, the L-4B's relay is too slow for that.

Michael Joens, K1JE
4 Sunnycrest Ave.
Beverly, MA 01915

--
FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm