NTE109 good replacement for 1N34A?

The only reason you'd see a germanium diode specified is because the circuit predates silicon diodes, or because the low forward signal drop is required. That any replacement is a germanium is the key factor, not the specific part number, in all but a handful of cases. 1N34s aren't hard to get because it's a hard to get number, they are hard to get because there is little demand for germanium diodes. Once you find a germanium diode, you are most of the way there.

Think of a "1N34" not as specifying that specific part, but as code for a generic small signal germanium diode. It's used because it traditionally could be had at small suppliers, which meant that it continued to be specified. I suspect much of the time, you'd not be getting a "1N34" but whatever they did have handy.

Micahel

You didn't say what RF you were going to detect, so it's hard to make a judgment. Looks okay but for a detector you might consider NTE583 which is the same as a 1N5711 schottky diode, made for RF detectors, mixers, etc. The V drop is half that of a 1N914 or 1N4148. The Ge diodes might be better for HFs but for VHF on up the 1N5711 is a good choice.