The following pictures show my BC-221C frequency meter. One picture shows the unit in operation using a home made power supply with my Opto 8000 frequency counter connected to the output. The frequency is 3.890Mhz after adjusting the unit’s VFO according to the tuning booklet that came with the unit (same serial number as the unit itself). The output frequency at the time of measurement was 20hz off frequency. The 120 volt supply supplies the +134VDC at 30ma and rectified 6.3 volt 2 amp filament voltage to eliminate hum in the audio and output RF signal. The filaments were factory wired for 6 volts therefore no need to change the filament wiring to accept 6VDC volt filament voltage.  The BC-221C is quite stable as it didn’t drift more then 10hz during that hour period. Not bad for a 60+ year old original factory assembled BC-221C. There was no evidence of “Golden Screwdriver” fiddling and all components and tubes are original. The unit was designed to operate from a 120 volt supply or “A” (filament) and “B” (B+) batteries.