You'll probably have to push in the SSB button to get the carrier down to around 100 Watts or so.
The amplifier will tend to overemphasize the carrier power, and underemphasize the peak modulated power.
The strategy of turning down the radio's carrier, so that it shows a higher proportion of 'swing' or modulated power serves to restore the balance between voice peaks and carrier.
But if the radio is stuck at 4 Watts carrier, your only solution is to turn down the input of the amplifier, so the carrier remains between 100 and 120 Watts, more or less.
The front-panel variable control on the amplifier is prone to burn out. It's just not rated for the heat a full 4-Watt carrier puts onto it. Keep that control turned up to full. Use the two push buttons labeled "AM" and "SSB" to bring the carrier down to the sweet spot. This will be less prone to cause a breakdown. Usually the SSB button alone will bring a 4-Watt carrier drive down to a safe level.
So long as the front-panel variable-drive knob is turned all the way to the right, it won't burn out, as a rule.
The carrier power coming out of the amplifier is what you need to be watching. No more than 120 Watts, more or less will just sound better. A higher carrier power makes the amplifier run hot, and reduces the audio level they hear at the other end of the conversation.
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