Les,
Yes, the NE612 should show plenty of gain. When it does not, the usual
reason is little or no oscillator signal to pin 6.
The Pre-mixer Bandpass filter must be aligned before you will get much
of a signal at U1 pin 6.
Since you have a 'scope (hopefully with a 10X probe), I will give you an
alternate method of tuning the Pre-Mixer Bandpass filter.
Since you have the 4 band board, you must follow the proper band order -
adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust
30 meters before 40 meters.
Make a check before starting - align all the slots in the trimmer
capacitors parallel with the long edge of the band board. Then check
the activity of the crystal for each band - put your probe on band board
P1 pin 4 and not the amplitude of the signal as you switch through the
bands - you should have greater than 200 mV peak to peak. The position
of the trimmer slots when tuned should be no more than 30 degrees from
the center position if your toroids are correct.
Then switch to 15 (or 17) meters, and with your probe on P1 pin 6,
adjust the Pre-Mixer trimmer caps for 15 meters for the maximum
amplitude. Switch to 30 meters and do the same for that bands
trimmers. Do the same for 20 meters and 40 meters. You should be able
to get 200 mV peak to peak there on all bands.
Remember that your 'scope probe will load the Pre-Mix filter a bit, so
the trimmers to the right of the filter will not be at their optimum
setting, but it will be enough for receive - you will set the optimum
position when you adjust for transmit.
You should check to see that the Pre-Mix signal is getting to U1 pin 6 -
if it is not, suspect the coax link on the bottom of the board between
J9 and J10.
Once you have a good signal at U1 pin 6, you should see that the output
at pin 4 is much greater than the input at pin 1.
73,
Don W3FPR
On 8/18/2014 5:20 PM, Les Garwood wrote:
Dear Fellows,
I Bought a K1 kit at a ham fest several years ago (SN 02197) and recently
finished the receiver section. Although audio is strong, as evidenced by
the hiss, I have nearly no signal on all 4 bands.
I can pump strong rf into it and hear a good side tone/bfo but not
strongly. Once, I heard a very faint CW station that was loud on my big
rig. But no others.
>From the best of my repeated testings, all voltages and resistances
provided in the manual match. I have not built an rf probe for my DMM yet
but will. However, I also used the signal generator kit from Elecraft
(the KXGI?). It is only weakly audible too, and only on the 50 microvolt
setting. The AGC setting has no effect. The attenuator kills the weak
probe signal when on.
One post I found after scouring the Net spoke of a very similar problem
that turned out to be a bad 2N7000, in the A Preamp stage, but I can't see
how that would affect signal sensitivity, only audio gain.
I also put a scope on pin one and pin 4 of U1, the Receiver Mixer. The
relative voltage was 3x higher on pin 1 than on pin 4. I would at least
have expected gain instead.
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