Floating the heater in a monitor is not usually possible because they
run the heaters on a regulated DC supply instead of using AC from the
flyback. DC obviously won't work with a CRT heater isolation
transformer. I have seen other Sony monitor CRTs with 5v heaters, so
it may be fine. If your monitor does use AC heaters, then you need a
true RMS meter to measure this voltage.




I did isolate the heater on a Sony monitor once years ago, it was a DC
heater but I disconnected the plug and then wound a couple turns of wire
around the flyback core and used that instead, it worked great for a day,
but the cathodes were shot so I added another turn and it was bright again
for an hour or so, then it got unusably dim again, added another turn and
the heater burned out. The picture did look fine while it worked though.