[Elecraft] K3 Speaker Amp Protection

[Joe Subich, W4TV]

 > http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf

This is an entirely different (and older) modification.  Output Mod
Rev C is designed to prevent damage to the right channel of the AF
amp when it is "open circuit" as it is when SPEAKERS=2 with a single
speaker attached.

The modification that Paul is inquiring about is designed to protect
the AF amplifier when the output is short circuited - e.g. connecting
a *mono* plug with SPEAKERS=2 - or in case of overload (a sudden static
"crash" or high level carrier with AGC=OFF) when using low (4 Ohm)
impedance speakers.

The latter modification has never been documented but I assume it
involves adding 2R2 or 2R7 resistors in series with the blocking
capacitor - perhaps replacing L13 and L16 on the KIO3 Audio Board.

73,

    ... Joe, W4TV


On 3/11/2013 10:41 AM, David G4DMP wrote:
> I wouldn't have thought this needed a mod kit, Paul. It only requires
> two 470 ohm resistors which the application note states will be supplied
> by sending an e-mail if required.
>
> http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf
>
> 73 de David G4DMP
>
> In a recent message, Paul Kirley <pkirley at fuse.net> writes
>
>> http://elecraft.365791.n2.nabble.com/K3-speaker-audio-gone-td7561739.htm
>> l#a7561747
>>
>> Because I prefer to open my K3 only in low-static months, it's time to
>> ask about the status of this mod, which hasn't yet appeared on the K3
>> mod webpage.  Will it be available within the next few months?
>>
>> 73, Paul W8TM
>