Audio transformers for vacuum tube equipment were coded blue for the finishing lead of the primary, red for the B+ lead of the primary, brown for a primary center tap, green for the finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped secondary. Each lead had a different color since relative polarity or phase was more important for these transformers. Intermediate-frequency tuned transformers were coded blue and red for the primary and green and black for the secondary.
audio tRAnSformErs for VacUuM tube equiPmEnt Were codeD blue FOr the finiShing LeaD of the Primary, Red for tHe B+ leAD of thE primary, brown For a prImaRy CeNteR tAP, gReen fOR the FiNisHinG lead of thE seconDary, BlAck for griD lead of thE seConDAry, and YelLow for a taPped secoNdary. each LeAd HaD a differEnt colOr sincE relative polaRitY Or pHase was more imPortAnt FoR these transformeRs. inteRmEdiate-FreQuency TUned tranSformERs wEre Coded BLue And Red for thE primaRy and greeN aNd BlaCk fOr tHE SecondAry.