If I recall, a 2N3055 can handle 15A on its own. It's the world's most common series pass transistor used in linear supplies. The beta, and in your use, the alpha, is relatively low. If your supply has 3, 1 is probably acting as a driver for the other 2, in a Darlington configuration. See if the bases of 2 are connected, and if the same 2 transistor's emitters, are connected through fractional ohm balancing resistors, to the output.
If you really had a DMM on ohms, instead of diode check, you would have read only read leakage. On diode check, you would get a slightly lower reading from base to collector, than base to emitter.
Frankly, if you were going to use a meter instead of a scope to troubleshoot, you started off on the wrong foot. Most of those units fail because their electrolytic capacitors dry out. Many of them derive a V++ supply with an extra diode and filter cap, to power the LM723. Don't go changing components until you've gone through with your DMM on AC Volts. More times than not, you'll find a substantial AC ripple voltage at 60 or 120Hz. If that isn't the problem, you could spot if the circuit is oscillating, not a good thing.
The current sensing will start coming into play when you get 0.6 or more volts between the output and current sense input, because you start biasing on the current limit transistor in the LM723. I don't have my datasheet open but the XX723, or sometimes 1723, has been around for decades, and is the most common regulator IC for linear supplies with external pass transistors.
The linear supply that I have to repair quite often is a +-15V, open frame, Lambda. It uses 2 LM723s, 2 2N3055s, and the separate V++ supply. The positive section is a straight forward design, with the emitter driving the output, and normal looking connections to the error amplifier. The negative output is not intuitive because the output is the negative supply rail, and the pass transistor connects to the common point. the error amplifier of the negative regulator is driven from a divider across both outputs, to make it "track" the positive regulator.
Joe
