Barry,

First, thanks for all the useful suggestions - I had set a slow 100 Hz
sweep, and applied a little averaging on the oscilloscope for the
response envelope. Alas, the spectrum analyser I have access to
bottoms out at 100 kHz, so the noise generator approach is no good for
me. That gimmick tip is ACE!!

I wouldn't personally discount the 'holistic' approach so generally. I
know that general component degradation has occurred with many of my
radios. As an example, most of the resistors in my HW-101 audio board
were outside of their tolerance. Electrolytics, we all know, have a
lifetime, and paper caps are known issues. Tubes do develop shorts and
some leakage. It's cheap and easy work to do - during which you find
the gross issues; with radios going past 50 years and several hands, I
have found it more likely that not that MORE than one issue will be
present. The complexity in the analysis goes up, sometimes 'by the
square' with each additional shortcoming. But you are right that one
has to eventually get down and perform an analysis of the operation of
a defective stage to come up with ways it could fail.

My method for a restoration is: *reading the manual*, visual
inspection, cleaning, switch/contact check and cleaning, tube check,
capacitor replacement (shotgun replacement of all paper and
electrolytic), resistor check, basic operating check, ALIGN if I've
changed anything in the RF circuits, then an full operations check.
I've found and repaired most of the latent issues by the time I get to
the last step, and I can have a fair amount of confidence in most
components being 'what they claim to be' when it does come time to
review the schematic for a particular issue.

David Goncalves
W1EUJ

You have my respect! Far too many hams do their troubleshooting of
vintage gear by first using a tube tester and then using a VTVM to
compare measured voltages to a chart. I have always recommended
that they first study the schematic until they understand the design
fully.