Tischfernsprecher 38 Wehrmacht Telephone (1943)

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The Tischfernsprecher 38 (TF 38) is a german military telephone introduced in 1938 and used by Wehrmacht in WWII. On my samples the date 1943 is stamped on various components. There is no manufacturer's label. Some of these phones appear to have been produced by the Berlin factory "Heliowatt", others by "Mix & Genest": most probably the production was shared among several industries.

The telephone is a local-battery model (OB=Orstbatteriebetrieb). A 1.5-3 V battery is needed to energize the carbon microphone circuit. Normally the 1.5 V battery was installed inside the accessory junction box. The set can be also successfully used on a normal phone line to receive calls (the microphone battery is always needed). There is crank magneto generator to produce alternating current for the ringer. A push-to-talk button on the handset activates the microphone. It can be useful to reduce local noise when listening.

The induction coil and earpiece are wired in a Wheatstone-bridge circuit to cancel locally produced sounds.

Interesting links (telephones and other stuff)

		The schematic diagram on the tag fixed to the bottom. The numbers 1-8 specify the wire color coding (picture courtesy of Karlheinz Weber)
		Phonetic alphabet table (Buchstabiertabelle)
		Carbon microphone
		Click on the image and learn how I restored my phone step by step
		I have two phones. In one of them, to save precious strategic metal, the ringer bells were made from pyrex glass. The magneto generator is painted red. The induction coil is on the right.
		The first two posts from the left on the terminal strip are used to connect the microphone battery (labeled "MB"). One wire of the phone line must be connected either to the third (La/ZB for normal phone lines) or to the fourth post (La/OB/SB). The other wire goes to the last post on the right (Lb/E). The large 4-pin plug on top connects to the handset. The bipolar socket is for extra headphones.

Some diagrams useful for repair

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