Arbiter reissues used AC128s. Hendrix also switched to the silicon transistors, but they created additional difficulties on stage, since they are much more susceptible to receiving AM radio signals, which were then audible through the guitar amplifier.
The passage describes a situation where Arbiter's AC128 models were reissued and Jimi Hendrix adopted silicon transistors in his guitar setup. The use of silicon transistors caused problems on stage because they were susceptible to picking up AM radio signals, which then interfered with the sound.