Hello! I'm building a 120 watt Ham AM transmitter around a pair of 807's in the PA and another pair in the modulator. Problem is I don't have a pin-out. It's a Merit A4005 with 12 terminals, is rated at 60-100 watts and the windings can multi-match 2-20K. I checked Bunker of Doom; no luck. Is there anyone out there with info? I'd really appreciate it. Thanks & 73! Mike-W9ZSL

The peak power out of a 100% modulated AM transmitter is four times carrier power.
I am not sure the 807s will survive long without good fans. If you have a shelf full of them, use good fuses.

About the transformer. Use a meter to determine the two (or more) windings. Draw out what you find.
(Some transformers have a tertiary winding to also modulate the final screen or the driver tube.)
Use the low ohm range to determine the connections on each winding.
The audio side uaually is one center-tapped winding.
The tapped side will feed the RF amp.
Use an audio oscillator and one volt or less across the audio side winding.
Start at one end of the RF winding and measure the voltage from it to each tap.
When the voltages are the same, the ratio is 1/1.

From the formulas and tables in the old handbook;
You know the level of load resistance you designed the audio tubes to see.
Use this value on the audio side winding.
You know the load resistance you designed into the RF amp output.
Determine the ratio of the two impedances.
This ratio must be matched with the turns ratio.

Simple ratio and proportion will give you the starting taps.
Trudge forward, the feeling of accomplishment when you start making contacts is worth it !
Pat