The ARC 65 is 99.9% tubes, but it does have a very nice 1.0 MHZ TCXO module that is solid state. 28 VDC in and a VERY stable 1.0000... MHz out. There are also a couple of solid state diodes in cans plugged into tube sockets formerly occupied by diode tubes. Did the ARC 21 have the same TCXO module?