1Y Mallory-Yaxley radio service encyclopedia second edition 1938. in the front it lists most of the radios mfg. up to 1938, listed by mfg. for the comet-pro it lists 7 diff. versions as follows...... ver 1))comet-pro battery........w/4-77's/2-78's/1-42 tubes ver 2) comet-pro dec. 31........w/2-24A's/2-35's/1-47/1-80/2-27's ver 3) comet-pro july '32.......w/2-24's/2-35's/1-37/1-80/3-27's ver 4) comet-pro feb. '32......w/2-57's/4-58's/1-2A5/1-80 ver 5) comet-pro sept.'32......w/2-57's/4-58's/1-47/1-80 oct.'32.......same comet-pro "standard model.....see ver.4 above ver 6) comet-pro crystal....same as ver.4 w/added xtal filter ver 7) comet-pro AVC model....w/2-57's/4-58's/1-2B7/1-2A5/1-80st of the radios mfg. up to 1938, lisYwYB K GY[B Arialer 4) comet-pro feb. '32......w/2-57's/4-58's/1-2A5/1-80 ver 5) comet-pro sept.'32......w/2-57's/4-58's/1-47/1-80