[Boatanchors] 600 ohm audio

[BLIMPY]

most common am transmitters allow you to pipe audio out the back by the 
bucket load via a 500/600 ohm tap.

Ranger
Valient
DX-100
AF-67

all can do this.

Many PA ampfliers also have a 600 ohm tap.

600 ohms is the the Broadcast Audio Std. Impedence.
And trust me any program amp you can find is hi-fi.

Antique Electronics Supply sells a HiZ to 600 Ohm transformer... meant to 
match single ended output stage to 600 ohm load.  They call it a Collins 
Collector Output Xfmr.

But I understand you wanting the original Halli/Mil speech amp.