Hi Keith,
Yes, that CRT heater current should have a trapezoid or square shaped waveform.
When looking at the schematics, the 6.3V CRT heater supply is generated through transformer TR1310B (schematics #11) This secondary side gets driven by the inverter circuitry in the power supply, see schematics # 9.
As there is current flowing, at least the CRT heaters seem to be intact and can be ticked off your check list.
Good Luck,
Magnus
