How do you check the filament voltage?
It would have to be checked by touching or connecting the probes of a voltmeter (or a multimeter set to measure volts) to the filament pins of one or more of the tube sockets, under the chassis, or to some other circuit points that are connected to those pins. (To assure a meaningful result the measurement should be done while the tubes are in their sockets, as opposed to removing the tubes and accessing the socket pins from above the chassis). Lethal voltages will be present on some of the other pins on those sockets, as well as elsewhere under the chassis. And if the probe tips were to momentarily come into contact with two adjacent pins simultaneously damage to the component may occur. So it’s a task that is best left to a qualified technician.
Also, regarding the references to 6.3vac and 7vac, many designs provide dc voltages to the tube filaments rather than ac. In those cases, of course, the meter function should be set for dc volts rather than ac volts, and the probes should be connected with appropriate +/- polarity.
Best regards,
-- Al
