The ADY20 is a PNP germanium transistor produced by Siemens. It is very similar to the ADY13. Both transistors offer a maximum blocking voltage of 45V and a maximum collector current of 600mA. One difference is the amplification factor, which is specified as 60-100 for the ADY20 and only 40-70 for the ADY13. As a side note, the base-emitter breakdown voltage of the ADY20 is slightly higher at 15V than the ADY13 which only allows 10V. 2H is probably a date code typical for Siemens, which would refer to the year 1976.
Unlike the ADY13, the ADY20 does not have a hole in the housing. Here, the housing has been filled with a desiccant that has accumulated on one side.
The design is very similar to the ADY13, which also uses a heatspreader. However, the emitter potential is supplied by a piece of wire and no longer by a metal strip.
The transistor was coated with a kind of protective lacquer.
The surface structure of the emitter contact suggests that different solder materials were used.
The surface structure of the germanium crystal is barely visible through the protective coating.
As with the ADY13, the germanium crystal is located on the dome of the heat spreader. At 70µm, the thickness of the germanium crystal hardly differs from the ADY13.
Here you can see a second ADY20. The housing looked exactly like the housing of the first ADY20 and a drying agent had also been used here.
Compared to the first ADY20, the protective lacquer is somewhat clearer here. Here, too, two different solder materials can be recognized.
However, the surface structure of the germanium crystal is just as difficult to recognize.
Here there is significantly more protective lacquer on the underside of the transistor. The contours of the germanium crystal are barely visible.
https://www.richis-lab.de/BipolarA56.htm 
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