[Elecraft] Q21

[Eric Swartz WA6HHQ - Elecraft]

The 2N5109 is the correct transistor for the preamp. While the 5179 will
work, it has a much noisier noise figure in this circuit configuration. We
originally designed it with the 5179 but were very unhappy with the results.
The 5109 is a much superior part.

I apologize for Scott's mistake! We were very busy this last week handling
the holiday order and support rush.

He may be sneaking into the office sometime next week, so go ahead and send
him an email requesting the 5109.

Most of the time the parts are not at fault. In the preamp we see almost
100% of the problems are due to improper toroid winding, tinning or lead
arrangement into the PCB.

73, eric  WA6HHQ
====

Ira Saber wrote:

> Because I am having difficulty with the proper functioning of the preamp
> in my new K2 (3076); and because I have exhausted just about everything
> that I could do; save replace Q21 in the attempt to get the preamp to
> amplify rather than to attenuate;  Scott @ Elecraft and I decided that
> replacing Q21 would be the last step in the cycle of fixes.
> 
> So, today I received from FedEx my new Q21.  Surprise!!  The replacement
> part does not look nor does its product number match the Part No:
> E5800013 in the K2 Manual.  The original Q21 is a metal jacketed
> transistor labeled 2N5109.  My replacement part is a standard appearing
> (D-Shaped, black body) transistor with the code MPS 5179 3030 stamped on
> the flattened surface.
> 
> Now, since Elecraft will be closed for their week long Christmas break
> (God knows they deserve it), I will not be able to call Scott and
> determine if the replacement transistor is in fact a true replacement
> that can be substituted for the original Q21.