Thank you Michael. Thank you Ty.
The TR50 test I described above was without any internal battery so that suggests the problem was not a function of negative bias. I did not think to switch inputs on the mixer, but I did cycle the connectors a few times. The mixer was a new SD 664 that seems to work flawlessly otherwise.
I contacted Tram by phone and spoke to a friendly tech. They asked me for the serial numbers (about 200 units difference), and they stated that the 10dB disparity is probably a quality control issue. They offered to exchange the mics at no charge. I’ll mail them out Monday and report back if the problem is not resolved when I receive the replacement(s).
These TR50s were purchased together from B&H, for what it’s worth.
Additionally, the tonal response of the two mics seemed markedly different (to my untrained ear at least).
Thanks again fellas.