Ask your friend how much ALC indication he's seeing when he talks. (Press the meter function select button until it displays ALC.)
The manual recommends setting the radio so that the ALC indication remains within the ALC zone (which will be indicated on the display). This is typically ok for SSB operation. For AM though, I would expect that under ideal conditions you would never see any ALC indication at all.
The ALC should be set not to let the radio exceed 100 watts at any time. In SSB mode, that means a voice peak can never push the transmitter beyond 100 watts -- if you try, the ALC circuit will kick in and throttle the drive level back to keep you in range. You want the mic gain set so that you modulate up to 100 watts without going over. Switching on the processor should also help you improve your average power too (while still not going over 100 watts).
For AM though, the rule is still that if you want 100% modulation, you need to set your carrier to one quarter of your PEP. So since the radio isn't designed to exceed 100 watts PEP, your carrier should be at 25 watts. If you increase the carrier beyond this, then the ALC will kick in on voice peaks and throttle back the drive again. And once it kicks in, it may take a short while to unclench -- how long depends on the circuit design.
This behavior is a little different from the typical 11 meter case where the carrier is set to high: in that case, you just run out of headroom for positive modulation. The difference is that in this case, you don't just hit the ceiling: you bounce off it and are pushed down, and then you slowly climb back up, due to the time constant in the ALC circuit.
With my rig (Kenwood TS-950SDX), max PEP is 150 watts. I can set the carrier at about 35 watts or so, and at that point I can still see 100% modulation on the scope with little to no ALC action. Be aware however that I'm also using compression in my audio chain to keep the audio clamped so that it never goes over a certain level no matter how loud I talk or how much I climb up onto the mic. That allows me to maintain 100% modulation without going over. It's the "without going over" part that's important here.
Note: the compressor feature built into the radio is not the same thing. This is usually for use on SSB modes only. On some rigs it has no effect on AM too.
From what I've read some radios may simply have much less forgiving ALC circuits. It may also be the case that some radios have the peak point set a little low (i.e. instead of set right at 100 watts, the limit is actually a little lower). This can make it harder to follow the "25 watt carrier" rule: even if you try to do things that way, the ALC may still kick in. I'm basing what I know on the Kenwood rigs that I have, and they seem to behave fairly consistently, but I haven't operated many other HF rigs in AM, so your mileage may vary.
Also, even if the ALC circuit isn't too fascist and you obey the "25 watt carrier" rule, if you have an amplified mic on the rig (like, say, a D-104) and the gain set too high, you can overmodulate and that too will cause the ALC circuit to kick in.
The current values your friend provided are a bit telling though. You said he's getting 12 amps when he first keys up. If we assume his power supply is set right at 13.8 volts, that works out to 165.6 watts of DC input power. Now if we're really pessimistic and assume only 50% transmitter efficiency, then his RF output power will be half of that, but that works out to 82.8 watts. That sounds like more than 30 watts RF carrier to me.
So my suspicion is that he just has the carrier set too high, and the ALC circuit in the radio is throttling him back.
In general, what I recommend that he try is:
1) Start with the mic gain and carrier control all the way down
2) Key the rig up and use the carrier control to set the dead key to 25 watts -- no more.
3) Set the meter on the rig to show ALC
4) Talk into the mic and gradually increase the gain until you just start to see some activity on the ALC meter
5) Check the output power level on the radio -- it should hit 100 watts on a voice peak
6) Check the current meter on the power supply and see how much it reads both on a dead key and with modulation
If I understand the math right, using just a sine wave for testing, your average power at 100% modulation (assuming a 25 watt carrier and 100 watt PEP) would be about 70 watts. Speech is a more complex waveform so don't expect to see exactly that number when you're talking.
As I said before, without any audio compression, it's difficult to get that "100% modulation without going over" behavior. Trying to manage the audio level manually means keeping your voice level constant and staying the same distance from the mic. It's hard to do that -- if you start talking louder or get closer to the mic, the you'll likely find yourself overmodulating and you'll see more ALC activity. Visualizing this without a scope to monitor your output is also very hard.
Lastly, in the interest of full disclosure, some some really troublesome radios, people have been known to try defeating the ALC by connecting a battery to the ALC input on the back of the radio. This is provided for feeding back the ALC voltage from an external amplifier. This can allow you to overcome an overly aggressive ALC circuit. However, keep in mind that the ALC circuit is intended to keep the transmitter operating within its design limits, so you should still try to keep the output at 100 watts. Driving it too hard can reduce the lifetime of the unit, and result in distorted output.
-Bill
