K3 and AL-811 amplifier interfacing...

[VK7JB]

Hi All,

Is it advisable to connect a K3 to an old AL-811 amp via a buffer/relay circuit, such as the ARB 704?

Or, is the K3 able to handle switching this amp without a buffer, making the ARB 704 unnecessary?

I'm hoping to simplify my connections and to do away with the Arb 704 if it's safe to do so.  

Thanks for advice.

John
VK7JB

[Todd - k1tm]

The AL-811 manual states that "Relay:  keys amplifier when grounded.  Sources +12 VDC open
circuit and supplies 100mA when grounded.  A built-in pulse canceling diode protects the exciter. "

The K3 is pretty robust "KEY OUT (RCA/Phono) is the amplifier T-R relay keying output, capable of keying up to +200VDC @ 5A."  The relay coils back emf is contained by the diode across it.

So, no issues switching the AL-811.  5A's and 200Vdc withstand voltage, beats 100ma and an applied 12Vdc source all day long.

73

[VK7JB]

Hi Todd,

Tnx for your note. I've removed the ARB704 interface and all is well. I've fingers crossed that the pulse canceling diode remains healthy. When I posted my question, I'd had trouble finding the specs on the K3 keying circuit in the manual - they're there, but couldn't find them!. I felt happy when I found it's so robust. 

Thanks for your interest. 

73

John VK7JB

On 08/09/2012, at 1:48, "Todd - k1tm [via Elecraft]" <[hidden email]> wrote:

The AL-811 manual states that "Relay:  keys amplifier when grounded.  Sources +12 VDC open
circuit and supplies 100mA when grounded.  A built-in pulse canceling diode protects the exciter. "

The K3 is pretty robust "KEY OUT (RCA/Phono) is the amplifier T-R relay keying output, capable of keying up to +200VDC @ 5A."  The relay coils back emf is contained by the diode across it.

So, no issues switching the AL-811.  5A's and 200Vdc withstand voltage, beats 100ma and an applied 12Vdc source all day long.

73

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NAML

[Mark Kempisty]

The AL-811 manual states that "Relay:  keys amplifier when grounded.  Sources
+12 VDC open
circuit and supplies 100mA when grounded.  A built-in pulse canceling diode
protects the exciter. "

<SNIP>


Several years ago the question of how much voltage and current does an Ameritron put in its key line.  I measured mine which was configured for 220V (I no longer have that amp).  I came out with around 14 or more volts and at least 100 mA, maybe higher.  Looking at the schematic there was no regulation on that circuit, it came straight from the transformer.  Since mine had more juice going in, it surmised that more was coming out.

So be careful if you connect a rig with a keying line that is not as robust as a K3's.

 
Take care,
Mark
AA3K
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