[Elecraft] Q21

[Dale M. Boresz]

Ira,

I checked the spec's for both the 2N5109 and the MPS 5179, and although 
the 2N5109 has a higher max. power dissipation, the circuit in which the 
transistor is used doesn't drive it hard enough to achieve that power 
dissipation. Both transistors are NPN transistors, and both are 
considered RF amplifier transistors, and I'd bet that the MPS 5179 will 
work fine in the K2's preamp circuit.

One word of caution though: Observe the orientation of the transistor. 
Refer to the diagrams in Appendix B of the K2 manual. If you hold the 
MPS5179 so that the flat side is facing you and the leads are down, pull 
the center lead (Base - "B") out toward you slightly, leaving the left 
and right outer leads where they were. The MPS5179 can then be 
maneuvered into position in the holes for the 2N5109. In other words, 
the flat side of the MPS5179 will face the control board, NOT the rear 
of the K2.

Good luck. I hope that solves the preamp problem.

73, Dale - WA8SRA


Ira Saber wrote:

> To: Any and all who wish to read/answer this e-mail
>
> 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.
>
> I would welcome a response by anyone with more information than I .
>
> Warmest regards and all the best for the Holidays and New Year to all 
> of those out there who read/respond to this e-mail.
>
> 73's         Ira, N2IS
>
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