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Old September 11th 03, 07:18 AM
The Eternal Squire
 
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Default need advice aligning a vaccum tube spectrum analyzer

Hello, everyone.

It looks like I have a new, exciting, rather daunting project ahead of me.
I'd like some advice
from anyone interested in providing it.

I have now adopted into my household (and home lab) a Lavoie LA-18M spectrum
analyzer unit,
circa 1950's, completely tubes plus a few microwave crystal diodes. I
also have a manual.

The manual is missing the overall schematic diagram of the entire unit but
has schematic diagrams
of all the major sections, such as the IF strips, and it also has general
troubleshooting procedure.

Given its age, it is in outstanding condition, because everything about it
works. Given the fact that
I bought it for only 50 bucks, as a working antique it is an absolute
treasure. However, I am concerned
about the weak signal sensitivity.

For calibration equipment, I have a late year 100 Mhz analog scope, a
Wavetek 3001 signal generator,
and a digital multimeter, if that helps.

With the signal generator I was able to determine that the minimal
discernable signal at 10 Mhz was
-34dBm. The manual on the Lavoie indicates that the sensitivity at that
frequency should be 40 microvolt,
so that seems to tell me that age has affected the sensitivity.

There are several IF strips on the unit, and the manual tells me which strip
needs to be aligned first, but
it does not go into any detail about how to align each of the IF strips for
best performance... it merely
says "replace IF strips as necessary".

If I had a time machine I could probably follow the manual's suggestions,
but short of that I am out of
luck there. I also understand that the alignment procedure for AM IF
strips is differerent from FM IF
strips, and for IF strips used by spectrum analyzers it could be different
still.

So, does anyone have any advice for me on how I should peak each vaccum tube
IF strip. I will supply
specific information on each, and will email scans of the schematics for
each, to those who want to
consider the problem.

Thanks,

The Eternal Squire


 
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