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K2 transmit low power, high current

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Wayne Conrad

K2 transmit low power, high current

K2 #7150 is assembled. It receives, but shows low power and high
current on transmit. Doing the 40 meter transmitter alignment
procedure, I get these results.

When not transmitting: 13.6V, 0.22A
TUNE, 5.0W selected: 5.0W indicated, 13.3V, 2.00A
TUNE, 10.0W selected: "Hi cur" warning, 5.8W indicated, 13.2V, 2.50A

During transmitter signal tracing, trouble first shows up in the
"transmitter mixer, buffer, band-pass filter, T-R Switch" checks:

(All measurements Vrms using RF probe, "key down")
Xmit mixer output (U10, pin 4): Expected: 0.16, actual: 0.0019
Buffer output (U9, pin 6): Expected: 0.200, actual: 0.0927
Ratio of Buffer output to Xmit mixer output: Expected: 12:1 Actual: 49:1
Band-Pass Filter Output (W6): Expected: 0.030, actual: 0.0318
T-R Switch #1 Output (D1 anode): Expected: 0.029, actual: 0.0305

The Pre-driver, Driver and PA voltages are, with one exception, also
unexpected, but I'm guessing that's a result of the previous stage being
all goofy:

(All measurements Vrms using RF probe, "key down")
Pre-driver output (Q5 collector): expected 0.120, actual 0.194
Driver input (Q6 base): expected 0.026, actual 0.017
Driver output (Q6 collector): expected 1.8, actual 2.8
PA input (Q7 base): expected 0.38, actual 1.19
RF detector input (D9 anode): expected: 2.0, actual 1.98

Where should I look next?

- Wayne Conrad

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Don Wilhelm-4

Re: K2 transmit low power, high current

Wayne,

The first place to look is the Low Pass Filters and possibly T4.
Make certain the number of turns on the toroids is correct - count the
number of times the wire goes through the center of the core rather than
counting turns on the outside. When winding a toroid, a straight wire
through the center of the core is one turn, a full wrap around the core
is two turns.
Check and double check the windings of T4. You should have two loops of
white wire and 2 white ends (3 turns) on the side away from the PA
transistors,
And on the PA transistor end you should see one green loop and 2 green
ends of wire (2 turns).
The link wires should go straight through the hole on one side and then
solder straight to the board - these do not loop through both holes.

Based on your readings, you may have a problem with the TX buffer (too
much gain), but that is not what is causing the HiCur messages and low
output.
After the HiCur messages are fixed, then double check the Buffer - check
resistor values and soldering particularly R93 thru R96 and C150.

73,
Don W3FPR

On 4/28/2011 3:38 PM, Wayne Conrad wrote:

> K2 #7150 is assembled. It receives, but shows low power and high
> current on transmit. Doing the 40 meter transmitter alignment
> procedure, I get these results.
>
> When not transmitting: 13.6V, 0.22A
> TUNE, 5.0W selected: 5.0W indicated, 13.3V, 2.00A
> TUNE, 10.0W selected: "Hi cur" warning, 5.8W indicated, 13.2V, 2.50A
>
> During transmitter signal tracing, trouble first shows up in the
> "transmitter mixer, buffer, band-pass filter, T-R Switch" checks:
>
> (All measurements Vrms using RF probe, "key down")
> Xmit mixer output (U10, pin 4): Expected: 0.16, actual: 0.0019
> Buffer output (U9, pin 6): Expected: 0.200, actual: 0.0927
> Ratio of Buffer output to Xmit mixer output: Expected: 12:1 Actual: 49:1
> Band-Pass Filter Output (W6): Expected: 0.030, actual: 0.0318
> T-R Switch #1 Output (D1 anode): Expected: 0.029, actual: 0.0305
>
> The Pre-driver, Driver and PA voltages are, with one exception, also
> unexpected, but I'm guessing that's a result of the previous stage being
> all goofy:
>
> (All measurements Vrms using RF probe, "key down")
> Pre-driver output (Q5 collector): expected 0.120, actual 0.194
> Driver input (Q6 base): expected 0.026, actual 0.017
> Driver output (Q6 collector): expected 1.8, actual 2.8
> PA input (Q7 base): expected 0.38, actual 1.19
> RF detector input (D9 anode): expected: 2.0, actual 1.98
>
> Where should I look next?
>
> - Wayne Conrad
>
> ______________________________________________________________
> 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
>

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Wayne Conrad

Re: K2 transmit low power, high current

Installing T4 correctly appears to have done the trick. Output power
went up and current draw went down, and seem reasonable.

The xmit mixer & buffer output voltages changed after fixing T4, but are
still out of whack:

All measurements Vrms using RF probe, "key down")
Xmit mixer output (U10, pin 4): Expected: 0.16, actual: 0.0009
Buffer output (U9, pin 6): Expected: 0.200, actual: 0.0692
Ratio of Buffer output to Xmit mixer output: Expected: 12:1
Actual: 76:1

I started making a chart of power & current on all bands and for
different power settings, intending to post it here to see if it's as
expected. But something seems odd to me: When I select 5W and key up
with the DL1 attached, the output power (measured at the DL1 with a VOM)
drifts upwards just as it does during TUNE. For example, in the 40M
band, key down output power starts at 5.4W but after 10 seconds is
6.1W. Is that right?

73,
Wayne (still studying for the test)

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Dave Anderson, K4SV

Rose the carrying case Lady

Hi All,

I wonder if Rose, who makes the great carrying cases for Elecraft gear, is on vacation or has changed her email. I have tried contacting her without reply.

Thanks in advance,

Dave Anderson, K4SV
Tryon, NC
828 777-5088

www.K4SV.com
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Iain MacDonnell - N6ML-2

Re: Rose the carrying case Lady

I believe the current address is [hidden email]

See also: http://tinyurl.com/7lm3m5

73,

~iain / N6ML

On Fri, Apr 29, 2011 at 7:05 AM, Dave Anderson, K4SV <[hidden email]> wrote:

> Hi All,
>
> I wonder if Rose, who makes the great carrying cases for Elecraft gear, is on vacation or has changed her email. I have tried contacting her without reply.
>
> Thanks in advance,
>
> Dave Anderson, K4SV
> Tryon, NC
> 828 777-5088
>
> www.K4SV.com
> ______________________________________________________________
> 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
>

Dave Anderson, K4SV

Rose the carrying case Lady, UPDATE

In reply to this post by Wayne Conrad

Hi Everyone,

Ken, Rose's husband called me today and let me know they are both under the weather but are feeling better and are on the mend. He said to let everyone know as soon as they are able they will be back doing business as usual.

Ken mentioned they have received emails and orders and will get to them just as soon as possible. So until then please be patient.

Dave Anderson, K4SV
Tryon, NC
828 777-5088

www.K4SV.com
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