I have an HP 606a and was planning to use it to calibrate my SX-101a,
which has a 50.75khz 2nd IF. Well... the generator won't go down below
about 55khz. I opened it up to calibrate it using an HP 5245L counter.
At the very top after about 62mhz, the output drops to about 55mhz if
you try an tune any higher. At the bottom, you can't get below 55khz.
Dials show capable of 50khz to 65mhz, and I believe I have read where
others have said it will go to 45khz. Checked the tubes... didn't
notice any bad components. The oscillator voltages at all pins are
bang on, as is the dial calibration on every band everywhere but the
extremes I mentioned (this was after I calibrated it). So is this just
the way they are? If not, does anyone have a clue what might cause the
oscillator to not be capable of the highest and lowest extremes? I did
notice the tuning capacitor trim tabs were used a fair bit, so I am
wondering if someone trying to get great dial tracking, which it has,
shot out the extremes in the process.

Do I have an option in calibrating the SX-101 by heterodyning the
100khz reference output of the counter (which is damn accurate) with
the HP 606 set at 150.75khz to get the 50.75khz I am looking for? If
so, do I hard couple, loosely couple or what? Will the other
frequencies running around in the radio cause any calibration issues?

Thanks a million for all the help this group has been to me. I repay
the favors when I am capable, and that is better every day.

Dan

geojunkie wrote:
I have an HP 606a and was planning to use it to calibrate my SX-101a,
which has a 50.75khz 2nd IF. Well... the generator won't go down below
about 55khz.

My 606A makes it to 49.6 kHz. Proper alignment (and maybe
replacing some fixed components that have drifted over time)
should get it there.


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Heterodyning is a good technique. Couple so you get a steady signal, don't
over or under couple. A little more than your counter needs for a lock
should be good. Remember that the sum of the two, 250.75KHz will be there
also, but shouldn't bother you ..
I haven't tried this at RF but you might also try feeding twice 59.75 or
101.5 KHz to a small germanium fulll wave or diode bridge and tapping the
ouput thru a small cap and that should give you 50.75, not as clean but
probably useable.
I just checked my HP 606A which hasn't been on in a year and it'll go down
to 49.45079KHz at the stop. I haven't looked at the manual becasue I'm not
sure where it is but I think the primary osc is LC with C variable, it must
be low on one or the other. It might be easiest to just jump the main
tuning cap with a small 20 or 30 mmfd mica cap to get it down for the job.
Later you might find out why it won't go low enough. Perhaps it some
componenet aging, a defective part or whatever.
good luck
hank wd5jfr
"geojunkie" wrote in message
om...
I have an HP 606a and was planning to use it to calibrate my SX-101a,
which has a 50.75khz 2nd IF. Well... the generator won't go down below
about 55khz. I opened it up to calibrate it using an HP 5245L counter.
At the very top after about 62mhz, the output drops to about 55mhz if
you try an tune any higher. At the bottom, you can't get below 55khz.
Dials show capable of 50khz to 65mhz, and I believe I have read where
others have said it will go to 45khz. Checked the tubes... didn't
notice any bad components. The oscillator voltages at all pins are
bang on, as is the dial calibration on every band everywhere but the
extremes I mentioned (this was after I calibrated it). So is this just
the way they are? If not, does anyone have a clue what might cause the
oscillator to not be capable of the highest and lowest extremes? I did
notice the tuning capacitor trim tabs were used a fair bit, so I am
wondering if someone trying to get great dial tracking, which it has,
shot out the extremes in the process.

Do I have an option in calibrating the SX-101 by heterodyning the
100khz reference output of the counter (which is damn accurate) with
the HP 606 set at 150.75khz to get the 50.75khz I am looking for? If
so, do I hard couple, loosely couple or what? Will the other
frequencies running around in the radio cause any calibration issues?

Thanks a million for all the help this group has been to me. I repay
the favors when I am capable, and that is better every day.

Dan