I used a dry rag and then coated the washers with a fresh coat of white lithium grease
that I obtained from the auto parts store. There may be a better grease to use and time
will tell if the lithium grease will work out ok. One other source says black moly-lube but
I couldn’t find that so I used the white lithium. Replace the washers with the tabs
pointing out toward the front. Make sure the outside washer has the hole for the collar
pin.
Replace the collar and lightly tighten the setscrew with very little play between the
washers. Attach a frequency meter to the RCA jack output of the LMO. Put the mode
switch to USB which is where the Heath manual has you start alignment. This is the
only switch other than the on/off switch that needs to be set to a particular position.
Insure that the loose controls from the front panel are not shorting out and then apply
power.
You will be setting the LMO to track between approximately 5.5 MHz. and 5 MHz. The
critical part is to get the counter clockwise stop to end up at around 5.5 MHz. and the
fully clockwise stop to end up at approximately 5 MHz. This may seem backward to you
until you recall (or check the circuit description in the manual) that the LMO tunes
backward from the actual frequency received. The LMO will actually tune a little bit more
than 0.5 MHz. wide and you will want to center the tuning range within this bandwidth.
Start out with the brass collar lightly tightened so that the shaft can slip beneath the
setscrew. Watch your freq meter and get one end of the tuning range within 10 KHz. of
the desired tuning stop. For example: 5.510 on the counter clockwise end or 4.990
MHz. on the clockwise end.
If you can get it this close you will probably have it close enough. Mine worked out this
way and the later dial adjustment required little change. Once you have the LMO within
this range, you can tighten the setscrew with your new ACE driver. The rest of the work
is done by following the Heath manual.
When I first approached the LMO problem with my SB-301 I thought I had made a
serious mistake in removing the collar and washers. I found that using the frequency
meter as above, I was able to get the LMO back to the original good adjustment. The
satisfaction and knowledge gained from this project gave me some of the enjoyment I
missed in not being the original builder of this rig and a renewed appreciation for the
guys at Heath who made it all possible.
Heathkit Linear Master Oscillators (LMOs) Page 131
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