[Elecraft] KX1 Please need help with T/R thump

[Don Wilhelm]

  Jerry,

All that transistor has to do is remain in an open state between the 
collector and emitter during receive and provide a path to ground 
between collector and emitter during transmit.  Any transistor that has 
a low saturation voltage will serve in that capacity - it is just a 
switching transistor.  I do not know why the 2N4124 was chosen other 
than that there are other 2N4124s in the KX1 design, and it is easier if 
most of the transistors are the same.

Try the 2N3904 and see what happens.  The worst thing that can happen is 
if you have to clip it out, you will lose the transistor, but they are 
quite inexpensive.

73,
Don W3FPR

On 5/26/2011 1:34 PM, Jerry W7ANM wrote:
> Don,
>
> I did extract the old Q7 without any damage or problems.
>
> I was looking at the spec sheet for the 2N3904 after getting your last
> suggestion and after ordering the 2N4124 from Elecraft. Do you think the
> 2n3904 is a superior replacement for the 2n4124? Any reason to suspect it
> would not work or why the 2n4124 was chosen for that circuit?
>
> 73,
> Jerry
>