[Elecraft] K1-4 Power Roll-off on 15 meters

[Thomas]

Howdy,

In one last desperate effort to solve a problem I am having with my =
K1-4, I am checking to see if anyone else been down this path as well. =
On 15 meters, the power will not increase much beyond 4 watts, with the =
power level set to 5W (12 or 13V supplies). The ALC is giving it all it =
has got, but there just isn't any more drive left. All of the other =
bands are good (maybe a little roll-off on 20 meters compared to the =
lower bands).

I've completely traced out the transmitter signal path using a TEK2465, =
300MHz O-scope. Everything looks okay, except the peak-to-peak voltage =
at the 50 Ohm load. I've checked every component's installation, pulled =
off the various transformers and coils and recounted their turns, and =
even measured their inductance using my MFJ259B. Everything peks right =
up during the alignment process.

I've tried reducing R11 to 68 Ohms as suggested by Elecraft, but do so =
made little difference. By the way, Gary at Elecraft has been offering =
suggestion after suggestion as well as measurement information. He has =
been very helpful. It is just that nothing seems to do the trick.

The only thing that looks a little suspicious is the PA collector =
waveform which looks a little less class-C like than on the other bands. =
This is before the low-pass output filter and you would expect it to =
look switching-like, with ringing. It comes closer to a sine wave than =
on any other band. Chances are the Ft (gain-bandwidth) of the output =
transistor is getting into the act on this highest band. In fact, I am =
starting to wonder if maybe I have a low Ft output device.

I have now spent more time trouble shooting this problem, then it took =
to build the K1-4. The receiver works great and the rest of the =
transceiver functions perfectly. I just can't get the full drive on 15 =
meters.=20

Thanks for your time, Thomas - AC7A (Tucson)


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