I assume this should be a 1N914 which is equivalent to 1N4148? Used to couple near the transmitters final tank of antenna matching inductor to monitor AM transmissions.

 

I would think so too.

 

1N914 seems logical, but the circuit looks like a crystal-set - wouldn't it need a germanium diode?

 

As it is from a TX final, there will be plenty of signal so the higher forward volts of the Si diode will not be such a problem.

 

The inductor (4-1.5" turns) is actually supposed to be put near the final tank circuit of an AM XMTR to monitor the signal. What caught my eye was the oddball diode which I assume was a misprint. Was poking around looking at some very basic XSTR or MK484 AM RCVR ckts. and came across it. Been picking up some parts for a while to play with some basic radio ckts. One of these days...

 

The 1N914 is a perfectly good detector just deaf compared to a 1N91 germanium diode. In this application it makes sense since sensitivity is not an issue and it is cheap as dirt and reliably available, and won‘t be picking up other stations on the same frequency when you are not transmitting.

 

I have had pretty good luck with the 1N5711 and BAS70-04. The BAS70-04 easily detects my microwave oven. Even a (genuine) 2N3904 can make a good detector into many tens of MHz.