The DD101 is a double signal diode designed for AC or DC mains. The heater current rating is 200 mA for use within a heater chain.
These are a pair of screened signal diode with application in HF rectification or demodulation. The design dates to 1938 when low capacitance diodes suitable for television were being developed.
The lettering is damaged but the second D and 101 are clear.
The reverse of the envelope is plain zinc paint.
The classic envelope is 32 mm in diameter, and excluding the MO base pins is 67 mm tall.
References: Data-sheet & 1043. Type DD101 was first introduced in 1938. See also1938 adverts.
