Historic Transistor Photo
Philco was an early manufacturer of transistors, starting in 1953/54 with the famous Surface Barrier type (SBT). This used a unique electrochemical etching process during manufacture that allowed for an extremely thin germanium base layer, which in turn allowed the transistor to operate at very high frequencies (20 to 30 MHZ). This operating frequency was substantially higher than that of alloy junction transistors of the time – Philco sold millions of these transistors in the 1950s to the military, to computer companies and to radio manufacturers. The SBT technology was improved by Philco, through the use of doping techniques, to develop transistors with even higher frequency capabilities. These improved SBT-style transistors were designated as MAT (Micro Alloy Transistor) and MADT (Micro Alloy Diffused Transistor). The 2N501 is an MADT type and represents one the highest performing of all these types – it is listed as functional up to 200MHZ. This type was also expensive, shown as costing $11.48 in the 1960 Lafayette Semiconductor Directory. These types of transistors were sometimes used by experimenters as RF amplifiers in home built radios. Other model numbers of the SBT/MAT/MADT type are SB100, SB101, SB102, 2N128, 2N588 and AO-1.
© 2002 by Jack Ward