thanks for communication - I know slightly more about symptom now --
first, it likely can't be what I thought - LPF - as this LPF also is used on 30 meters! my 30m power is okay.
I just ran a sweep across all the bands into a dummy load -- every band except 40m is producing a lively output (my power meter is reading 10 watts on 160m * down to 4 watts on 10m -- its got a QRP scale, but it was calibrated a couple decades ago). So I am convinced I have a substantial dip (reading less than 2 watts now on 40m).
since I am using a dummy load - I will get some data on the width of this notch. it is almost like a choke isn't working around 7 MHz.
brief history: my ubitx has always been weaker on 40m. I will confess it has one modification - an extra 45 MHz xtal filter placed on the other side of its IF amplifier. this network made the 40m outage worse. I saw a tip from Farhan to reduce R26 from 470 to 220 ohms to compensate for this filter loss - I made this mod. but I can't blame it directly -- I got nice output on all other bands.
we have 22 other ubitx from the same or recent lot in our club -- maybe mine is acting different that the population -- we are still gathering data from builders.
the funny thing - these kind of problems always increase education, getting 'me' to examine places I would not be compelled to examine. let's see if I can learn anything, and get this thing fixed.
* yes I realize I have no low pass filtering of the second harmonic when operating at 1.8 MHz ... but my 160m vertical presents a dreadful match at 80m. a nearby RBN receiver conveys I got at least 40 dB rejection by its non-report on 80m! know your antenna before doing this - but several of us in NA operating a stock ubitx on top band.