Elecraft

K2 Early Ver. A Power out problem #2438

Classic

List

Threaded

3 messages Options

Jimithy66

K2 Early Ver. A Power out problem #2438

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Don Wilhelm

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

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

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Jimithy66

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

---------- Forwarded message ---------
From: Jimithy66 <[hidden email]>
Date: Thu, Jun 13, 2019 at 10:16 PM
Subject: Re: [Elecraft] K2 Early Ver. A Power out problem #2438
To: <[hidden email]>

Hi Don, the K2 is #2438
And has been sitting around half built for 18 years or so :-0

The manual for Rev. A calls for 16 turns for L25 and L26 and they are 16
turns.

I will order the K2PAkit, and I have a good solder sucker and the wooden
toothpick is a great idea. Thanks...

R50 is 1/2 watt.

With the PA transistors removed will check the bias circuit and reflow Bias
solder
joints before changing Q11 and Q13.

Too bad there wasn't an easy way to isolate bias from the PA.

Don, as a side note,
If I touch a meter lead to R61, the collector of Q13, (PA bias) the 40m
output power jumps up to 7 watts with Hi Cur displayed.
Other than that the power barely reaches 2 watts with 1.9 amps.

Thanks again Don,

Jim / W1FMR

On Thu, Jun 13, 2019 at 5:36 PM Don Wilhelm <[hidden email]> wrote:

> 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
>