update older k2

[Richard Haendel]

I have an opportunity to purchase a second K2, serial number 008xx.  It has the SSB and noise blanker modules installed.  What upgrades/modifications are suggested to bring it up to at least the S/N 4500 performance?

Any suggestions are appreciated
Rich W3ACO K2 S/N 4023
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[Don Wilhelm-3]

Rich,

I suggest you download the K2ATOB instructions and look at the list of
changes shown there - there are several 'optional' parts that IMHO should be
included as part of the task.  In addition to the A to B changes, add the
PLL Temperature Stability mod and the Keying Waveshape mod - and while you
are at it, add the 2 diodes for the Strong Signal Handling addition (there
is no parts kit for this, just order 2 1N4148 diodes) - the mounting details
for the diodes is on page 59 of the K2 Rev F manual.

In addition, change the IF filter crystals on both the RF Board and the SSB
option and rewind T7 to the turns ratio indicated in the Rev F manual.
Check the resistors on the SSB option ALC area to see if the latest resistor
changes have been made.  While you have the SSB option crystals removed,
change the SSB filter capacitors to the newer values if you desire the wider
OP1 filter.

Last but not least, look it over carefully for any 'special purpose' mods
that the previous owner may have added and either remove them or satisfy
yourself that they are useful for your purposes.

Having done all that, you should have a K2 that performs up to the level of
the current shipped kits.  You may also want to optimize the AGC Threshold
for best reception (on the pre-SN3000 K2s this involves changing the fixed
resistor Control Board R1 (lower its value).

73,
Don W3FPR

> -----Original Message-----
>
> I have an opportunity to purchase a second K2, serial number
> 008xx.  It has the SSB and noise blanker modules installed.  What
> upgrades/modifications are suggested to bring it up to at least
> the S/N 4500 performance?
>
> Any suggestions are appreciated
> Rich W3ACO K2 S/N 4023
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Elecraft web page: http://www.elecraft.com
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[Andrew Moore-4]

I am performing a K1 transmitter offset alignment as described on page 47 of
the manual (Rev C, October 9 2000).  According to the manual I should
install a jumper between the two "OFS" pads, disable AGC, set output to 1
watt, and enter Tune mode.  At that point I should hear two tones - a
sidetone, plus a transmit monitor tone.

I hear neither.  If I key the paddles, I hear the side tone.  But Tune mode
doesn't produce any sidetone, nor can I hear the transmit monitor tone.

Any ideas?



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[JT Croteau-2]

This may help.

K1 Builder Alert #3: Inability to hear transmit signal when making the TX Offset
Adjustment
26 Feb. 2001

Impact: All K1's

Background:
When making the 'Transmit Offset Adjustment' (K1 Rev D manual, page 47) on some
K1s no TX signal tone is heard. (This adjustment has you match the K1 sidetone
frequency with the TX offset.) The reason this happens is because on some rigs
we have two mute circuits that work almost too well. Q10 is a shunt mute FET,
and Q11 is a series mute FET. Jumpering OFS (as noted on page 47)  prevents Q10
from muting, but it does not prevent Q11 from muting. Some J309s mute so well
there is not enough AF signal leakage from U3 to U4 to be heard in the speaker.
TX offset can still be set using an external receiver as a reference, but the
following procedure is suggested if you want to use just the K1.

Modification to TX Offset Adjustment instructions. (Please read the TX Offset
instructions on page 47 first.):

1. Set the RX BFO properly first (K1 Rev. D manual page 40), by adjusting C20
until maximum amplitude is found using an AC voltmeter on the AF output, or
using Spectrogram to peak the AF signal on noise.

2. Then turn off the sidetone completely (StL 0).

3. Set the power level for 2-3 watts.

4. Jumper OFS.

5. Try adjusting TX BFO trimmer C13 to see if you can hear the beat note. If you
still cannot hear the TX-generated tone, temporarily place a resistor of 47k to
100k across the Drain and Source leads of Q11 to allow more audio to leak into
the AF amp at U4. Now you should be able to hear the TX tone well.

6. You can then increase StL to 1-5 or so to match the sidetone and TX signal
levels. You may need to adjust the StL and Power level slightly so both are at
about the same audio level for hearing the beat note.

7. When the TX offset adjustment is complete, remove the OFS jumper and the 47k
to 100k resistor from Q11.

--
 JT Croteau - W6FO - Canton, GA | K1 #292
 ARS #2,147 | NoGA-QRP | SEDXC | ARRL
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