The results of the first and second plug-in of the phone revealed some issues with the ringer as it sounded more like a buzzing / vibrating sound in both the soft and loud settings than a ringing bell sound.
Overview of phone with dial removed.
Overview of M1A Ringer as seen from above.
Ringer at "soft" setting.
Ringer at "loud" setting.
M1A Bias Spring in High Tension Notch Position.
Clapper distance to gong before any adjustments.
For more details, see this related message/post on Classic Rotary Phone Forum.
None of these quick fixes made a difference in the sound quality of the ringer in either the soft or loud setting.
(Note that the black ringer wire has been put back on G on the 4010 B Network.)
I then found the M1A BSP and posted it to the forum.
Member poplar1 confirmed that the distance between the clapper and gong may be the issue:
http://www.classicrotaryphones.com/forum/index.php?topic=12714.msg134046#msg134046
"Try loosening the gong, then turning it. The hole is off center, so when you turn the gong, it will increase or decrease the distance between the clapper and the gong.
The biasing spring has 2 notches; you might try the other notch.
2.04 The 61A gong is eccentric. Clearance between gong and clapper shall be 0.010 to 0.020 inch. Resonator is built-in and needs no adjusting.
2.05 Bias spring is factory set in the high notch. It can be repositioned, as required, to either high or low notch with long-nose pliers.
BSP C18.048 issue 1, Oct. 1962"
Rotating gong around axis.
This is the furthest point to the clapper.
Rotating gong around axis.
This is the closest point to the clapper.
Unfortunately, rotating the gong did not alter the clearance distance significantly enough to make much difference in the vibrating / buzzing sound quality of the ringer.
The following steps contain short video clips and have been separated on different pages to more easily review the repair changes and compare the ringer sound differences by opening in different browser tabs / windows.
With notes about repairs attempted and resulting ringer sounds.
Related posts/messages on the Classic Rotary Phone Forum:
Related Bell System Practice (BSP) Documents:
Additional 702B BSPs are on the Resources page.
The project / repair links on this website can be found here (in order of repair):
Next step in sequence: