Wow. Is all that circuitry really necessary? I built a pretty simple solid
state interface between my TS940S (and, later, TS950SDX) and my SB-221 when
I did Rick Measures' QSK mod. Following Rick's design, I used only one
small bipolar transistor and a couple of resistors acting as a voltage
divider. Of course, the SB-221 mod included dropping the relay voltage down
to 24V from 115V and the Jennings vacuum relay probably draws a lot less
current than the L4B relay. But you could always use a bigger bipolar. Now
I use a small variation on the circuit to drive my 87A's 5V T/R sensor (and
another one to mute my DSP 59+.)
With all the QSK amps around these days, it's a wonder that the
top-of-the-line transceivers don't include solid state amp switching with
current overload protection and variable voltage selection.
73, Dick, WC1M
----------
> From: Garry.&.Yelena. <ni6t@scruznet.com>
> To: JOHN.BASILOTTO. <basilj@tamug.tamu.edu>
> Cc: Amp.Reflector. <amps@contesting.com>
> Subject: Re: [AMPS] Icom 756
To: <amps@contesting.com>
> Date: Thursday, March 20, 1997 12:40 AM
>
> JOHN BASILOTTO wrote:
> >
> > I have an Icom 756. I was using it with a Drake L4B. At first
everything was
> > fine; after about 30 days the reed relay in the Icom froze stuck. The
Icom
> > relay is rated at 16volts@2amps. The Drake amp has a 12 volt relay but
has a
> > potential of 26volts with no load. Consider using an aux. relay;
otherwise
> > you too may have to replace an Icom relay.
> > 73, John w5GI
> >
> I have an L4B. The changeover relay has a 24 volt coil in my amp--if
> yours is 12V, perhaps someone botched a repair. My L4B did not have a
> quenching diode across the relay coil--perhaps it was the transient that
> fried your relay! Install a rectifier, backwards, across the relay coil,
> either directly, or on a small terminal strip.
>
> One alternative to avoid problems like you describe is to install a
> small circuit in the amplifier to allow control of the amplifier's relay
> with low voltage and very low current. This is readily accomplished with
> a CMOS inverter (4069), NAND gate (4011) or NOR gate (4001) driving an
> N-channel MOSFET. Radio Shack's IFR510 will do nicely. Put a pullup
> resistor in the gate input, and bypass the input to ground. For the L4B,
> power the gate with a dropping resistor off the relay supply (about 150
> ohms, 0.5W), 12 V zener and bypass caps. With a pullup of 22K, <.5 mA
> controls the relay. If the radio also provides a lead from the collector
> of the transistor controlling its internal relay, you can use that and
> disable the internal relay. Ground the inputs of the 3 unused gates or 5
> unused inverters.
>
> As long as you are at it, you can add two diodes, an electrolytic, a
> resistor and a small NPN to "kick" your amp's relay with a
> double-voltage transient, which will speed up the changeover and
> increase the life of your relay contacts. This has been covered before
> and is on K6XX's web page--ask n0ss for the URL (n0ss@socketis.ne).
>
> The small board can easily be mounted on standoffs near the relay
> supply, running the lead from the relay control jack along the existing
> harness and securing it with cable ties. As an added precaution, run the
> input and output leads through a ferrite bead where they connect to the
> board. This and the bypassing should preclude RF pickup problems.
>
>
> --
> Garry Shapiro, NI6T
> Editor, "The DXer," newsletter of the NCDXC
> Visit the Northern California DX Club 50th Anniversary page:
> http://www.aa6g.org/ncdxc50.html
>
> --
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