[Elecraft] K3 AF Upgrade Kit (for speaker amplifier and LINE OUTs)

[Leigh L. Klotz, Jr WA5ZNU]

I installed this last night in K3#51.  I'm running uC 2.67, which 
features the AGC-OFF hearing protection.
I'm trying to decide what LINE OUT and AGC setting to use for digital 
modes with.

If AGC is disabled, line out values 0, 1, 2, 3, and 4 produce strong 
differences.  After that I see almost no change in output.
If AGC is enabled, even moderate signals produce enough AGC action (even 
if AGC threshold is pegged) so that I need LINE OUT of 30 or so to get 
enough output.

For now I get the best results in data modes with AGC OFF and a LINE OUT 
level of 5.

Leigh/WA5ZNU
> This information and a mod manual are now on our K3 Enhancements and
> Applications note page. See:
>
> http://www.elecraft.com/K3/k3_app_notes.htm
>
> I apologize for the delay getting this posted! It should have been up
> earlier.
>
> >From that page:
>
> Line-Out KIO3 R19/R20 Change:
> About Oct 7, 2008
> About S/N 1900
>
> Speaker Amp RFC47 Change:
> About Sept 25, 2008
> About S/N 1830
>
> (Dates and serial numbers are approximate and may vary slightly.)
>
> 73, Eric   WA6HHQ
> ------
>
> N6WG wrote:
> > I would also like to know that please.
> > 73, Igor UA9CDC
> >
> >> Wayne
> >> Can you tell us the serial number at which
> >> these changes were incorporated?
> >> We need to know who needs to order them
> >> and who does not.
> >> Thanks and 73
> >> Bob N6WG
> >>
> >> ----- Original Message ----- From: "wayne burdick" <n6kr at elecraft.com>
> >> To: "Elecraft Reflector" <elecraft at mailman.qth.net>
> >> Sent: Thursday, November 13, 2008 10:40 AM
> >> Subject: [Elecraft] K3 AF Upgrade Kit (for speaker amplifier and LINE
> >> OUTs)
> >>
> >>
> >>> With minor circuit changes, both the K3's speaker amplifier and line
> >>> outputs can provide lower IMD (intermodulation distortion) at higher
> >>> signal levels. We've been testing these changes for a couple of
> >>> months, and have already phased them into production.
> >>>
> >>> These changes can easily be made to existing K3s. A kit of parts is
> >>> available (K3AFMDKT). All parts are leaded (not surface mount), and
> >>> full instructions are provided. See:
> >>>
> >>>    http://www.elecraft.com/order_form_parts.htm#K3%20Parts
> >>>
> >>> Details
> >>> -------
> >>>
> >>> SPEAKER AMP:  The mod kit includes a very low-resistance RF choke
> >>> for use at RFC47 on the RF board. This improves speaker amplifier
> >>> IMD by as much as 25 dB at moderate to high AF GAIN settings by
> >>> reducing the voltage drop across RFC47 during signal peaks.
> >>>
> >>> LINE OUT:  The kit also includes smaller resistor values for R19 and
> >>> R20 on the KIO3 module. At present R19 and R20 are about 600 ohms,
> >>> while the replacements drop the resistance to around 50 ohms. The
> >>> smaller resistors increase the available voltage swing at the output
> >>> of the LINE OUT transformers, which improves IMD at higher signal
> >>> levels.
> >>>
> >>> These two changes are independent. For example, if you never use
> >>> LINE OUTs, you might want to do only the speaker amp modification.
> >>>
> >>> 73,
> >>> Wayne
> >>> N6KR
>
>
> wayne burdick wrote:
>> With minor circuit changes, both the K3's speaker amplifier and line 
>> outputs can provide lower IMD (intermodulation distortion) at higher 
>> signal levels. We've been testing these changes for a couple of 
>> months, and have already phased them into production.
>>
>> These changes can easily be made to existing K3s. A kit of parts is 
>> available (K3AFMDKT). All parts are leaded (not surface mount), and 
>> full instructions are provided. See:
>>
>>    http://www.elecraft.com/order_form_parts.htm#K3%20Parts
>>
>> Details
>> -------
>>
>> SPEAKER AMP:  The mod kit includes a very low-resistance RF choke for 
>> use at RFC47 on the RF board. This improves speaker amplifier IMD by 
>> as much as 25 dB at moderate to high AF GAIN settings by reducing the 
>> voltage drop across RFC47 during signal peaks.
>>
>> LINE OUT:  The kit also includes smaller resistor values for R19 and 
>> R20 on the KIO3 module. At present R19 and R20 are about 600 ohms, 
>> while the replacements drop the resistance to around 50 ohms. The 
>> smaller resistors increase the available voltage swing at the output 
>> of the LINE OUT transformers, which improves IMD at higher signal 
>> levels.
>>
>> These two changes are independent. For example, if you never use LINE 
>> OUTs, you might want to do only the speaker amp modification.
>>
>> 73,
>> Wayne
>> N6KR
>>
>> ---
>>
>> http://www.elecraft.com
>>
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