Re: K2 Early Ver. A Power out problem #2438

Posted by Don Wilhelm on Jun 13, 2019; 9:36pm
URL: http://elecraft.85.s1.nabble.com/K2-Early-Ver-A-Power-out-problem-2438-tp7653063p7653067.html

Jim,

Can I assume this is a newly purchased kit?  Or are you building an
older one that has been sitting on someone's shelf for a long time with
Rev A boards.  A serial number would be helpful - above SN 2999 will use
Rev B boards.

Given that you have 1.4 volts on the base of the PA transistors, you
likely have one PA transistor zapped and the other may be weak.
Get the K2PAKIT from Elecraft (it contains matched PA transistors).
It also has replacements for Q11 and Q13 if needed and a replacement for
R50 if yours is not already 1/2 watt.  It also contains new PA standoff
mounting hardware.

First remove the PA transistors.  If you do not have good removal tools,
clip the leads near the transistor body and remove the leads one at a
time.  Clean up with solder wick and if solder remains in the holes,
heat the solder pad and push it out with a wooden toothpick.

Now do a TUNE and measure the voltage at one of the base solder pad.  It
should be 0.60 to 0.64 volts (0.8 volts is too high)  If it is not
within that range, replace Q11 and Q13 and reflow the soldering on the
components in the bias circuit.  Do NOT install Q7 and Q8 until the base
bias circuit is working correctly.

After those checks (and only after), install Q7 and Q8.  Do not transmit
without the heat sink installed if you value your new PA transistors.

If this is an older Rev A kit, how many turns did you wind on L25 and
L26?  The older Rev A uses 14 turns which is different than the newer kits.

73,
Don W3FPR

On 6/13/2019 3:33 PM, Jimithy66 wrote:

> I finished building a basic kit with no options and the power output will
> not rise above 2 watts and current (2A) is too high for that power.
> Hi Cur flashes briefly before power output settles at 2 watts.
>
> Voltage checks found the PA base bias circuit putting out
> 1.4 VDC but  0.8 V is expected.
>
> Two PN2222A transistors Q11 and Q13 make up
> the bias circuit and wonder if anyone else remembers
> seeing this problem, and what may have caused it  ?
>
>   Thanks,
>
> Jim / W1FMR

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