SX-101a Tuning Capacitor Trim Tabs?
 

Sorry to bother you all again. I was cleaning about 40 years of smoke
off the chassis and afterwards noticed that one of the "leaves" on the
oscillator section of the main tuning capacitor was bent. I assumed I
must have done it while cleaning and straightened it back out before I
gave it much thought (how most mistakes happen). Then it dawned on me
that the last "leaf" of each section (there are 3 sections) is broken
into easy bendable "tabs" and is not a solid semicircle. So some
adjustment was allowed for. Now I am thinking I may have altered what
should have been. This wouldn't concern me so much if anything in the
alignment procedure covered how to make this adjustment, but I haven't
seen anything like that in my prior alignments. So, how do I check
this and possibly reset them correctly? I assume that they relate to
keeping the oscillator tracking right on with the RF tank tuning that
the other 2 sections are doing. But, I have never really noticed these
tabs bent as much as these were, so that is why I put them back. I am
noticing that a lot of my lessons are self-inflicted. I learn a lot
though, diving into things most people never touch. Hopefully someone
has some experience with this.

Dan

"geojunkie" wrote in message
m...
Sorry to bother you all again. I was cleaning about 40 years of smoke
off the chassis and afterwards noticed that one of the "leaves" on the
oscillator section of the main tuning capacitor was bent. I assumed I
must have done it while cleaning and straightened it back out before I
gave it much thought (how most mistakes happen). Then it dawned on me
that the last "leaf" of each section (there are 3 sections) is broken
into easy bendable "tabs" and is not a solid semicircle. So some
adjustment was allowed for. Now I am thinking I may have altered what
should have been.

Rotsofluck. Gads... That was probably a factory only adjustment.
Your best bet is to carefully check several positions across the dial
for dial tracking errors. What you will have to do is carefully adjust
each plate (starting fully meshed) for minimal dial error. As you increase
frequency, the moveable plate about to unmesh is the one you want
to adjust for frequency (osc) and strongest AGC (RF/Mixer). Here's
the rub... The mechanical alignment interacts with the electrical
alignment..
One shouldn't sub for the other. So, first thing is to see if the radio
is working good enough at this point. You might be best leaving it
alone??

Pete

On Tue, 23 Dec 2003 15:56:27 UTC, (geojunkie) wrote:

Sorry to bother you all again. I was cleaning about 40 years of smoke
off the chassis and afterwards noticed that one of the "leaves" on the
oscillator section of the main tuning capacitor was bent. I assumed I
must have done it while cleaning and straightened it back out before I
gave it much thought (how most mistakes happen). Then it dawned on me
that the last "leaf" of each section (there are 3 sections) is broken
into easy bendable "tabs" and is not a solid semicircle. So some
adjustment was allowed for. Now I am thinking I may have altered what
should have been. This wouldn't concern me so much if anything in the
alignment procedure covered how to make this adjustment, but I haven't
seen anything like that in my prior alignments. So, how do I check
this and possibly reset them correctly? I assume that they relate to
keeping the oscillator tracking right on with the RF tank tuning that
the other 2 sections are doing. But, I have never really noticed these
tabs bent as much as these were, so that is why I put them back. I am
noticing that a lot of my lessons are self-inflicted. I learn a lot
though, diving into things most people never touch. Hopefully someone
has some experience with this.

Dan

Oopsie, bad move.

Easy to fix. (I'm guessing as I've never tried it but mull it over.)

Figure out which section you bent. If you are certain it was just
the oscillator. Do this:

Map out the motion of the capacitor against the indicators on the
tuning dial. Figure out where the breaks occur and which end of
the dial, the cap is at full un-mesh.

The SX-101A had 5 kHz markings and was non-linear. This makes it
easy. You're not trying to align something like the Heathkit LMO,
linear and 1 kHz marks.

Make a table of the frequency vice the divisions (petals) on the
cap, which end is at 14,000 and what is the oscillator freq when the
dial is at 14,000.

Hook up your frequency counter. Work from the unmesh end and tune
to the marks on the glass dial that correspond to the breaks in the
plate. Bend the first plate to "ooch" the frequency counter onto
frequency.

Check it at the middle and both ends of that petal. Might take a
few tries but you should be able to get it very close.

Then move to the next petal. You mesh another segment.

The trick is to get the oscillator tracking the glass dial. Since
the resolution of the SX-101A is only 5 kHz, you should be able to
get it as close as the factory.

This would be a big deal if you didn't have a frequency counter.
Modern counters are good and inexpensive.

Others are encouraged to jump in and offer advice or corrections.

Good luck!

de ah6gi/4