Using a base-collector strapped transistor as AM detector, sharper knee for better weak signal demodulation
How to test a regular or SMD bipolar NPN or PNP transistor with a DVM in diode mode, to tell it apart from a dual common anode or cathode diodes inside a 3 legged SMD devide.
Using a small signal silicon transistor with its collector and base tied together makes the collector turn on once the base is biased on, making a sharper knee. Making for a good weak signal AM radio station demodulator. Collector saturation doesn't seem to be an issue.
I kept the silicon diode (D3) that came with the radio for the AVC circuit (R29 and a new 0.01uF cap to ground), and used a transistor with its base and collector tied together for the audio signal detector function. I split off the audio signal path (R30, C38) off the now AVC diode and put it on this transistor. Transistors like a 2N2222 or other silicon small signal types should work well. A sharper "diode" (base-emitter of the base-collector strapped transistor) knee will make for better reception of weak stations, if you add bias to overcome this "diode" (base-emitter) drop voltage. This is done with some forward bias current to improve weak signal detection, as this bias will help overcome the "diode" (base-emitter) drop loss of signal. A base-collector strapped transistor with a higher drop but sharper knee would be the better choice. Too many variables to calculate the resistor value to use (what current on the "diode" (base-emitter) knee will make it detect best, what's your supply voltage, what's the voltage of the "diode" (base-emitter) drop voltage, what's the resistive load on the "diode" (base-emitter) circuit such as the volume control, and so on), so trial and error would be quickest.

The emitter on such an NPN transistor would be the cathode, and the base tied to the collector is the anode Here I used a 2SC2785 salvaged from a VCR or such. If the transistor is a PNP, its emitter would be the anode, and its base tied to its collector the cathode. Try various transistors. I found that 680K seems to hit the sweet spot in this radio, but it's not a critical adjustment on a trimpot (which you can use to quickly find the value you'd want in a fixed resistor). I had thought that using a transistor this way was the mark of a sloppy company (did they run out of diodes?), but I got the best weak station detection performance with this. Oh, check strong stations too, which worked well too.

Some simulations of a diode, a base-collector strapped transistor,

and such a transistor with a bias current.

I'm not sure how much, if any, knee can be below 0V here. Conduction on the other side of 0V would probably mess up the detection. IIRC, the FCC requires that 10% be the minimium amplitude of an AM station's carrier, which should permit some knee curvature of stations that aren't too weak (else signal to noise would make them unlistenable anyway).

Above is an AM radio, a GE C1432, that was designed and built using a base-collector strapped transistor as the detector. The AVC circuit provides the bias to overcome the diode drop. Stronger stations will produce AVC voltage which will change the bias voltage, but this change won't much matter as the stringer station will overcome any mismatch of the bias vs the diode drop voltage.

How to test a bipolar regular or SMD transistor with a DVM in diode mode, to tell it apart from a dual common anode or cathode diodes inside a 3 legged SMD devide.

You know the old loose bipolar NPN or PNP transistor test method of checking the PN junctions (with your DVM in diode mode), like from the base to the emitter, and then base to collector. You can figure out if it's an NPN or a PNP transistor (compare to a diode). And additionally, you can see some transistor activity by doing this following test: First, having one test lead on the emitter and the other on the base (but not the collector), in the direction you see a diode drop voltage, typically you'd see about 0.68V on a silicon transistor. Now while keeping the same test lead on the emitter, touch at the same time with the other lead both the base and the collector. You should see a lower voltage like 0.59V (around 85% lower). This test can also tell you, with surface mount devices, if you really have a transistor, or a device with two diodes, one with a common anode, or a common cathode on what would look like the base pin.