High quality, very heavy, laboratory grade HP AC-60B bridging 10k/600:600ohm audio transformer. Mastering quality 1950s audio transformer equivalent to a UTC LS series at an affordable price. Flat from 20Hz to 45kHz - please see attached specifications. $35 new in 1955, this would be a $400 transformer purchased today after adjusting for inflation- an extremely high quality transformer for the time period.