SB-102 LMO Question

[Glen Zook]

The HW-101 did NOT use an LMO but used a much less
accurate VFO.  There is no comparison between the
physical layout of the HW-101 VFO and the LMOs.  The
sealed units are all LMOs.

There were several different part numbers on the tube
type LMOs.  

It has been my experience that the solid-state LMOs
used in the SB-102 were not as carefully calibrated by
the vendor (not TRW) as were the tube type LMOs.  The
solid-state ones are usually "right on" at the 100 KHz
points but can vary all over the place in between (I
have seen a couple that were over 5 KHz off in
"tracking").  The tube type LMOs are usually very
linear and track very closely.

I have like 4 or 5 solid-state LMOs right now that
aren't worth a darn in tracking.

The previous owner may have gotten rid of a poorly
tracking solid-state LMO and went with the tube type. 
The circuitry between the SB-101 and SB-102 are very
close and it would not be difficult to build the
sideband switching voltage circuit for the tube type
LMO instead of the solid-state version.

The 6BZ6 and several different tubes were used because
of the series-parallel arrangement on the heaters
("filaments") of the tubes.  The electrical
characteristics and base diagrams were the same but
the current required by the tube heater was different.
 The tube heaters are wired in various combinations so
that the current requirements are equal.  There may be
2 tubes in parallel that are in series with a 3rd and
so on.

Glen, K9STH

--- Bob Krassa <bob at KRASSA.COM> wrote:

I have just acquired an SB-102 with a tube type LMO -
it appears to be a stock SB-102 in all other respects
- board numbers match the manual, etc...my questions
that I hope someone can help with are:
 
1. Without taking the LMO apart (and the little red
paint dabs on the screws are unbroken), is there some
way to tell if this is the LMO from the SB-101 where
the tube serves as the oscillator, or if it is the one
from the HW-101 where there is an internal FET
oscillator and the tube is just the LMO amplifier?

Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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