K2 barefoot + ALS-600

[Derf Mockford]

Hi Ron, Phil & Don,

further to your item below on the Elecraft reflector, I use the
ALS600 with a barefoot K2. I appreciate that the required level of
amp gain is illegal to supply in USA but customer mods are quite
legitimate. The amp is ideal throttled-back for 400 watts max in UK.

By removing the amp's 35 ohm input series resistor and the 33 ohm
parallel resistor (3 x 100 ohms in parallel) that is across the amp's
input transformer, the input impedance came down considerably.
Using the K2 ATU, on 14.1MHz, 13 watts in = 600 watts out.

The primary of the amp's input transformer was one turn only. It is
Now re-wound with 3 turns as in the (almost identical) Communication
Concepts EB104 amp.  Input impedance is fairly close to 50 ohms for
1.9 to 20MHz. 6 watts in = 600 watts out. On 21 to 28 MHz, i/p Z is a
bit off of 50 ohms, and up to 10 watts is required for full output.

A 2db 50 ohm pi-attenuator was added on the input so that it is now a
good match to the barefoot K2 and suits UK max power limits.
I have no ALC connection from the amp to the K2, simply adjusting the
K2 RF output to get the required RF from the amp. The amp is very
stable and all mods took about 3 hours to complete.

The ALS-600 includes the AD5X QSK mod. This was the first mod that I
applied to the amp after purchase. Works perfectly. Phil, many thanks.

To you all and to the many contributors to the Elecraft reflector,
Merry Christmas.

73
Derf G8ZGK

>
> Subject: Elecraft Digest, Vol 80, Issue 42
> Message: 27
> Date: Mon, 20 Dec 2010 19:49:00 -0800
> From: "Ron D'Eau Claire" <[hidden email]>
> Subject: Re: [Elecraft] OT: modifying your amp for lower drive requirement
> To: <[hidden email]>,            "'Phil & Debbie Salas'" <[hidden email]>
> Cc: [hidden email]
> Message-ID: <000f01cba0c2$020458d0$060d0a70$@biz>
> Content-Type: text/plain;        charset="us-ascii"
>
> Sure, but it's very easy to design a low-loss broadband matching network to
> provide the required impedance transformation.
>
> One HB amp of mine used a 16:1 transformer at the input for just that
> purpose.
>
> Ron AC7AC
>
> -----Original Message-----
> Phil,
> Your statement amplifies the difference between "ham assumptions" and
> reality.
> The data-sheet indications of gain do not consider the input impedance
> (and loading of the driver), that parameter is quite important in actual
> use -- if the amplifier does not provide a good load to the driving
> transmitter, then "all bets are off".
> 73,
> Don W3FPR
>
> On 12/20/2010 8:28 PM, Phil & Debbie Salas wrote:
> "It's very unlikely any solid-state amplifier uses an input attenuator:
> Transistors and FET's just don't have that much gain."
>
> The Ameritron ALS-600 has about a 15 ohm input impedance.  Then they put a
> series 35 ohm resistor for matching and reducing gain.
> Phil - AD5X

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[Jim Brown-10]

On 12/22/2010 9:44 AM, Derf Mockford wrote:
> The amp is very
> stable and all mods took about 3 hours to complete.

If you're running the barefoot K2 higher than 10 watts, you should
probably take a careful look at the output of the ALS600 on a good
spectrum analyzer.  I've heard good engineers familiar with the K2 say
that it's spectral purity degrades above 10 watts, which is why Elecraft
considers it a 10W radio.

73, Jim K9YC


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[Dick, K2ZR]

Mark, More on the K2 barefoot + ALS-600 from the Elecraft reflector.  Dick

Jim Brown wrote:

>On 12/22/2010 9:44 AM, Derf Mockford wrote:
>  
>
>>The amp is very
>>stable and all mods took about 3 hours to complete.
>>    
>>
>
>If you're running the barefoot K2 higher than 10 watts, you should
>probably take a careful look at the output of the ALS600 on a good
>spectrum analyzer.  I've heard good engineers familiar with the K2 say
>that it's spectral purity degrades above 10 watts, which is why Elecraft
>considers it a 10W radio.
>
>73, Jim K9YC
>
>
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>
>
>  
>

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[AC7AC]

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