More miseries on K2 #5061

[M. P. Haynes]

Hello again folks,

I seem to still have that black cloud hanging over me as I finish the
basic K2 #5061.  

I am finishing the calibrations and adjusting the L's and C's in the
bandpass filter section.  I had 1 1/2 problems remaining.  All the
circuits tuned properly in receive mode except the 30 meter/20 meter
bandpass filters.  They would not resonate no matter how I screwed the
slugs in or out or adjusted the trimmers on 20.  I took the unit to an
engineer friend (K4POZ, who retired from chief engineer for WSB radio in
Atlanta) and he verified that I had assembled the circuits correctly and
had no solder splashes or missed connections. (He recently completed his
own K2)  He noted that when the slug on L9 was all the way in, the signal
started an ever-so-slight increase in output.  Figuring the circuit was
resonant too high, he added a 39 pF cap across L9 and the signals could
then be properly tuned on 30 meters.  The trimmer C23 rotor plate had
come disengaged (popped out) as I had attempted to tune it earlier and a
new one was sent by parts.  I anticipated that would solve my last
problem but to no avail, so 20 meters is still down about 70 dB or more.
I rechecked all components in the circuit and all are installed
correctly.  Has anyone ever seen this problem before?  Suggestions?  By
the way, I solder filled all the through-holes around this circuit just
in case there was a poor plate-through feed.  No change.

73,

Pat Haynes-K4BEH
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[Don Wilhelm-3]

Pat,

Additional questions:
1) does L8 peak properly?
2) How far down is the slug on L9 with the added 39 pf capacitor?

The tuning slugs are normally only a couple turns down from the top - if
yours are more than 3 turns down, something is wrong.

Since the bandpass L9 showed a peak on 30 meters with the paralleled 39 pf,
then I would surmise that either C24 or C25 is open. and the most likely
candidate is C25.  As your circuit is arranged now, it may tune to 30 meters
but without  divider created by the series combination of C24 and C25
properly connected, the impedance of the filter output will not be correct,
and is also a likely reason why you do not find a proper peak on 20 meters.

I would suggest that you arbitrarily replace both C24 and C25 unless you
have means for removing them without damage and measuring them for proper
value.

BTW - poor plated thru holes are truly a rarity, especially with boards of
Elecraft quality.

73,
Don W3FPR

> -----Original Message-----
>
> I seem to still have that black cloud hanging over me as I finish the
> basic K2 #5061.
>
> I am finishing the calibrations and adjusting the L's and C's in the
> bandpass filter section.  I had 1 1/2 problems remaining.  All the
> circuits tuned properly in receive mode except the 30 meter/20 meter
> bandpass filters.  They would not resonate no matter how I screwed the
> slugs in or out or adjusted the trimmers on 20.  I took the unit to an
> engineer friend (K4POZ, who retired from chief engineer for WSB radio in
> Atlanta) and he verified that I had assembled the circuits correctly and
> had no solder splashes or missed connections. (He recently completed his
> own K2)  He noted that when the slug on L9 was all the way in, the signal
> started an ever-so-slight increase in output.  Figuring the circuit was
> resonant too high, he added a 39 pF cap across L9 and the signals could
> then be properly tuned on 30 meters.  The trimmer C23 rotor plate had
> come disengaged (popped out) as I had attempted to tune it earlier and a
> new one was sent by parts.  I anticipated that would solve my last
> problem but to no avail, so 20 meters is still down about 70 dB or more.
> I rechecked all components in the circuit and all are installed
> correctly.  Has anyone ever seen this problem before?  Suggestions?  By
> the way, I solder filled all the through-holes around this circuit just
> in case there was a poor plate-through feed.  No change.
>
>

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