[R-390] analysis chart

[Dan Merz]

Thanks to all for their thoughts on the analysis chart that I found with my
radio.  I knew the engineer that owned this previously only through his son,
who by the way also is a radio station engineer at a Seattle station.  I
don't think he particularly shares his dad's intrique with these old sets
but I'm sure would appreciate  comments when I run into him again.  I am
currently restoring the original  6K7/6F8 tube pair that were converted to
6J5/6SN7 to provide audio from this set to the station transmitter using a
cathode follower output instead of driving the original power amp that is on
a separate chassis and that will be part of the restored radio.  As I go
through the set,  I'll watch for any changes that may be reflected in the
analysis charts he left in his files.  I've already identified some bad
electrolytics.    Since this is a 1939 radio,  it has a large number of
waxed paper caps,  some of which were already replaced before I got the set
several years ago.  I suspect I'll find a few more bad ones but I'm
generally not one to replace these on a wholesale scale unless the leakage
affects performance in an obvious way.  My thanks again for the comments,
Dan.

  _____  

From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Tisha Hayes
Sent: Monday, February 09, 2009 9:37 AM
To: r-390 at mailman.qth.net
Subject: [R-390] analysis chart


It sounds like the author was developing a good understanding of circuit
analysis. This is very similar to the process you go through when designing
a new receiver or transmitter; Since each circuit (RF, IF, mixer, AF,
detector, oscillator, etc...) has it's own characteristics you need to have
a keen grasp of how each circuit behaves, then you need to expand that
understanding out to the device at large.

I spent many years designing VHF/ UHF receivers and the process described is
a very important, and often overlooked phase of design. Usually at that
point in a product development cycle, the marketing group wants to produce
full color slicks and turn prototype equipment over to some alpha-site
customer. As an engineer I have always felt pressured to skip or shorten
this process. Every time you could fight off marketing, bean-counters
looking at the engineering dollars spent or some arbitrary time-limit you
could always pull a few more dB out of a design.

I admire this long forgotten engineer that was going through that process on
the radio you have. While he may not have made a tremendous improvement on
how the radio performed, I am certain that he had a great learning
experience.

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