Re: [KX1] Variation in driver transistors (e.g. 2SC2166)

Posted by Don Wilhelm-4 on Feb 10, 2011; 1:19am
URL: http://elecraft.85.s1.nabble.com/KX1-Variation-in-driver-transistors-e-g-2SC2166-tp6010045p6010228.html

  Chip,

If your goal is to get more than 4 watts out of your KX1, I would
caution against trying.  If you are attempting to obtain more power when
running with internal batteries, it is fine to try it, but when
operating with a 13.8 volt power source (or any other voltage) and the
power is greater than 4 watts, I strongly suggest you back off on the
setting of the R1 pot to protect the components in the output of the PA
transistor.  Note that the Eleflow 2SC2166 datasheet rates the
transistor for the 3 to 4 watt range.

Elecraft used the 2SC5739 in the KX1 for a period of time when it looked
like the 2SC2166 would not be available.  It worked well, and produced a
bit more output on 20 meters, but the new KX1 kits are shipping with the
2SC2166 again.

You can try if you want - the parameter that should be investigated is
the power gain.  A simple hfe measurement may not reveal changes in the
power gain.  Current Gain (hfe) does not directly infer power gain.

I would suggest that if you want more output on 14 MHz, change to the
2SC5739.

73,
Don W3FPR

On 2/9/2011 6:50 PM, Chip Stratton wrote:

> Just wondering here. How much part to part variation do devices like this
> display in their gain characteristics? If I had ten of these transistors, is
> there a good chance I could identify one with significantly better gain
> and/or power efficiency than the average? Would a simple measurement of hfe
> identify such a part, or is it more complicated than that?
>
> I've seen a Youtube video wherein a guy who sells 2SC2166 devices made by
> Eleflow substitutes this for the Mitsubishi made part  and seems to get a
> bit more power output out of a CB transmitter. Is this likely to represent a
> gain of efficiency of the final amplifier, or is it just a part that is just
> needs a lower bias to operate at its best?
>
> Thanks,
> Chip
> AE5KA
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