[BULK] - [Amps] IC-718 and AL-811: Icom manual misleading, interface nec...

[Martin J. Morgenbesser]

Thanks for your responses, guys.

The SOA explanation makes sense to me, if it were a solid state device 
doing the switching. But as Steve points out, the IC-718's "send relay" is 
in fact a physical relay, as depicted in the schematic. And if it is rated 
for 16V @ 2A, as the manual suggests, it should be able to directly handle 
the 12V @ 100ma present on the AL-811's relay line.

However, given the Icom representative's stated reluctance to consider it 
Icom's fault if the IC-718 send relay were to fail under those operating 
conditions, I decided to spring for the ARB-704. Ironically, the ARB-704 is 
a solid state device, but one capable of handling the Al-811's relay line!

The bottom line: Icom needs to do a better job of stating the technical 
specs in their manual, or give the customer the benefit of the doubt. Of 
course, now I won't have to test their willingness to do the latter.

In any case, I'm very happy with the IC-718/ARB-704/AL-811 combination. The 
amp keys beautifully and puts out a solid signal. Plus, thanks to the 
ARB-704, I have an additional red LED letting me know I'm keying the amp. :-)

One other thing, if Tom Rauch is reading this: Thank you for designing such 
a nice amplifier that can be had at a very reasonable price!

See you all on the air!

At 11:36 AM 2/4/05 -0800, Steve Katz wrote:
>SOA is surely something to consider, except the IC-718 uses a keying relay 
>for the amplifier "SEND" function.  Check the schematic.  They rate it 
>"16V, 2A," without any consideration for simultaneous or not; however, 
>that still begs the question, "Why only a 16V rating for relay 
>contacts?"  It's an amazingly low rating, even for tiny TTL 
>relays....-WB2WIK/6
>-----Original Message-----
>From: Japerlick at aol.com [mailto:Japerlick at aol.com]
>Sent: Friday, February 04, 2005 11:22 AM
>To: stevek at jmr.com; W7MJM at arrl.net; amps at contesting.com
>Subject: Re: [BULK] - [Amps] IC-718 and AL-811: Icom manual misleading, in 
>terface nec...
>
>Actually, this is quite common in transistor switching 
>applications.  Transistors (whether FETs, Bipolars, IGBT's whatever) have 
>have "Safe Operating Areas" which is a technical term for the range of 
>simultaneous voltage and current levels it can safely sustain.
>
>For example, the venerable 2N2222A is rated at 75 Volts VCBO, 40 Volts 
>VCEO and 0.6A max Collector Current...but the max power dissipation is 0.5 
>watts.  Obviously you cannot sustain 75V at 0.6A 
>SIMULTANEOUSLY.   Manufacturers specify a safe operating area--usually in 
>chart form--showing how much current the transistor can pass for given 
>voltage conditions--both in forward and reverse bias conditions.  It's 
>important to note that these charts do not necessarily correspond to a 
>simple curve of the maximum power dissipation.
>
>Combined with safe operating areas is the consideration of junction 
>temperature.  Almost all of these specs are given for device junctions at 
>25 degrees C (about room temperature).  Of course, you can imagine, the 
>ratings degrade at higher temperatures.  Overtemperature and overvoltage 
>are the two most common transistor-killers.
>
>So, yeah, the Alpha guy is probably right...you can't get both max voltage 
>and max current simultaneously....and it is not that simple.