K2: BFO range problem on early S/N K2

[Allan Taylor]

Hi,

We are working on an older K2 (S/N 152) to fix apply some simple mods
and generally update things. After doing some straightforward mods
 (control board exclusively) we decided to touch up the filter/BFO
alignment as the perceived bandpass seemed to be tuned a bit low.
 It went very easily until we were working on the CW filter settings in
CW-REVERSE. There, anything we did refused to shift the bandpass
appropriately. We then did a BFO test from the manual. The desired range
is 3.5 kHz or higher, this rig came in at 2.83 kHz and is likely the source
of
our problem. Reading somewhat in the manual, a L33 is referred to. We
haven't
pursued that angle as yet. So... the big question for the K2 gang is this:

what is the most likely cause of a too-narrow BFO tuning range? I personally
suspect the BFO crystal(s), but what do I know.

For reference, I did not build this particular unit although I did build a
K2 of the
same S/N series back in 2000. This K2 has not been used much at all but
seems to work fine otherwise.  This K2 got a ride on three major raft trips
this
past summer (in a Pelican case!) but I doubt that is the source of the
problem.

Any ideas? Things to check??

--
73     Allan    K7GT
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[Don Wilhelm-4]

Allan,

Not only is your range restricted, but likely the minimum and maximum
frequencies are not as indicated in the manual.

While your suspicions about the BFO crystals may be correct, there may
be other problems with soldering, L33 or the capacitors used.

For the easiest solution, order a set of BFO crystals and the BFOMODKT.  
Check the value of C173 - if it is other than 220 pF, get one of those
capacitors too - a new C174 comes with the BFOMDKT.

While you are at it, you might want to consider doing all the other A to
B mods, change the IF filters and KSB2 crystals to the newer crystals
and do all the other modifications indicated in the K2 A to B
instructions, including updating the firmware.  Your K2 will perform
better for it.

73,
Don W3FPR

On 12/11/2013 2:47 PM, Allan Taylor wrote:

> Hi,
>
> We are working on an older K2 (S/N 152) to fix apply some simple mods
> and generally update things. After doing some straightforward mods
>   (control board exclusively) we decided to touch up the filter/BFO
> alignment as the perceived bandpass seemed to be tuned a bit low.
>   It went very easily until we were working on the CW filter settings in
> CW-REVERSE. There, anything we did refused to shift the bandpass
> appropriately. We then did a BFO test from the manual. The desired range
> is 3.5 kHz or higher, this rig came in at 2.83 kHz and is likely the source
> of
> our problem. Reading somewhat in the manual, a L33 is referred to. We
> haven't
> pursued that angle as yet. So... the big question for the K2 gang is this:
>
> what is the most likely cause of a too-narrow BFO tuning range? I personally
> suspect the BFO crystal(s), but what do I know.
>
> For reference, I did not build this particular unit although I did build a
> K2 of the
> same S/N series back in 2000. This K2 has not been used much at all but
> seems to work fine otherwise.  This K2 got a ride on three major raft trips
> this
> past summer (in a Pelican case!) but I doubt that is the source of the
> problem.
>
> Any ideas? Things to check??
>

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Please help support this email list: http://www.qsl.net/donate.html