In article , Gary Schafer
writes:

I set the carrier level out at 20 watts. Modulated the transmitter
with a 1000 hz tone up to 100% modulation as seen on the scope
monitoring the output of the transmitter.

What sort of rig?

Using a drake w4 watt meter
(same as a bird) the watt meter held steady at 20 watts. It read the
same at full 100% modulation as it did with no modulation, just the
carrier. No ALC involved here either.
Watching the scope the rf output voltage did double with 100%
modulation as would be expected.

Now had I put a thermocouple rf ammeter in the coax line I would have
seen an increase in the line current with modulation.

But you didn't put an RF ammeter in the line, nor an RF voltmeter.

What did I do wrong?

I don't think you did anything wrong. What sort of rig was it? How modulated?

73 de Jim, N2EY