Zenith radios used
transistors from many different manufacturers, and developed a unique
numbering system to identify the many different types of transistors used
in Zenith radios. As shown below left, the Raytheon 2N111A/CK759A
transistor used in the Royal 500 was also stamped by Zenith with the type
identifier “121-10”. Zenith used the “121-xxx” system for many years,
through the 1960s, to identify hundreds of different transistors used in
various models of Zenith radios. Shown above is a cross-reference list recently
developed by Ray to identify the more standard “2N” EIA types that
correspond to the “121” numbers of the transistors in his Zenith Royal 94/990
Inter-Oceanic radio, which recently failed to function after 40+ years of
frequent use. He was able to repair the radio by replacing a failed AM/FM
oscillator transistor with an Amperex 2N3588. In addition to the “121”
numbering scheme, Zenith also began using “421” in the 1960s. Zenith sold
replacement transistors to dealers for repair purposes – for example, the
Raytheon 121-10 shown at left was sold as a 1950s Zenith replacement part
in packaging shown at middle left. In 1973, the Zenith Components and
Accessories Division initiated the Cross Reference Sales Program (CSRP)
which made a broad range of replacement transistors available. These were
identified by the “ZEN XXX” numbering scheme. Shown above left is an
example of a CRSP ZEN302 germanium replacement transistor, which can be
cross-referenced to the Raytheon 2N111A transistor shown at left.
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