1744 – By that year or earlier, George Kraft built an organ for the original stone church which stood across Mifflin Street. This small instrument was moved into the present building when it was opened in 1766.
1774 – David Tannenberg of Lititz, Pennsylvania, built an organ of 2 manuals and pedals containing 20 stops. The case was built to Tannenberg’s specifications by Peter Frick, a Lancaster joiner. The original part of the case includes the two large towers and everything between. It is one of the most magnificent American organ cases to survive from the 18th century. It was also the largest and most expensive piece of American furniture when built.
1854 – Henry Knauff of Philadelphia built a new organ, retaining the Tannenberg case and many of the pipes.
1887 – Hilborne Roosevelt of Philadelphia installed a new organ of 2 manuals and pedals, having 26 ranks. He also retained the case and many of the former pipes.
1893 – Bernard Mudler of Philadelphia re-arranged the Roosevelt Organ in an enlarged case (8 pipes were added on both sides of the large towers). This enlargement allowed for better egress of sound.
1923 – The firm of Casavant Frères, St. Hyacinthe, Quebec, Canada, installed an organ of 4 manuals and pedals, with 42 ranks of pipes. 16 of these ranks were retained from the former instruments, with all of the pipes being contained inside the case.
1962 – M. P. Moller, Inc. of Hagerstown, Maryland, installed a completely new instrument of 4 manuals and pedals.. All the pipe work, mechanism and console were newly installed inside the historic case of David Tannenberg, and outside in two divisions between the case and the walls. The S.D.G. Organ Service Co. of Millersville, Pennsylvania, built the new console, installed the new control mechanisms, and added two sets of pipes to the organ. James R. McFarland took over the care of Holy Trinity’s organ in 1974 following the Moller Factory service. During this time, many improvements and refinements were made to the instrument. The Walker Technical Co. of Zionsville, Pennsylvania, founded by Robert Walker, installed the digitally synthesized pipe ranks, with many samples taken from Aeolian-Skinner Organs. Their “state of the art” technology made it possible to “fill in the gaps” where pipe ranks were lacking in Holy Trinity’s organ because of space constraints. They provide “color” and fundamental (lower) sounds that the organ did not possess.
2001 – The S.D.G. Organ Service Company of Millersville, Pennsylvania, built a new console within the old shell and completely replaced the old relays and combination action with a computerized solid-state system. Thousands of electrical wires going from the console to the relays in the tower were replaced by a single cable about the size of a lamp chord. Three new sets of pipes were also added. The Walker Technical Company of Zionsville, Pennsylvania added digitally synthesized pipe ranks to the instrument. The organ now has the equivalent of 99 ranks, 55 pipe and 44 digital.