Tischfernsprecher 38 Wehrmacht Telephone
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. 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) with provisions to operate also on a central-battery system (ZB.) A 1.5 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 still needed). There is crank magneto generator to produce alternating current for the ringer. A push-to-talk (PTT) button on the handset activates the microphone. It can be useful to reduce local noise when listening.
The TF38 was not intended for rough use as the FF33 field telephone. Tischfernsprecher means table top telephone, and in fact it was meant for use in offices and barracks, or even inside trains like in the photo below.
Hitler and Franco meet at Hendaye on October 23, 1940, aboard the Führersonderzug special train. A TF38 is between the two.
Interesting links (telephones and other stuff)
My two TF38s
My two phones appear to have been built in 1943-44. They were abandoned in Pisa in my parents' house in 1944 by retreating German troops. They are very well preserved and were used for some time with a private line inside the house. I remember very well that one had the connection/battery box (Beikasten) but that has been lost since a long time. Also, one had capacitor C1 shorted (maybe because of a contact with a power line) but this did not prevent it from working in a local-battery setup.
It is interesting that, in one of them, to save precious strategic metal, the ringer bells were made from pyrex glass. For both the base plate is bakelite but others have a metallic base. The magneto crank handle housing was also missing in both.
I stored these phones for more than 60 years. When I was a teenager I realized that the audio was very weak. I tried swapping on of the receivers with the one of my father's office phone (made by Siemens) and I discovered that the volume improved a lot, so I decided that the receiver permanent magnets had lost their magnetism and I confiscated the new one. Needless to say that the office had to call the serviceman and have the receiver replaced!
Occasionally in the past I checked the the phones and I realized that the internal wiring developed intermittent problems, probably because of loss of insulation (a very thin silk layer, I believe,) some capacitors developed leaks (and C1 was shorted since the beginning.) For me a vintage apparatus has some value as a collection item only when working properly (see my surplus radio gear pages) so I decided that a rewiring and re-capping of the phones was in order. Of course I tried to preserve the external appearance of the circuit components, and below is the result.
For Sale
I have now decided to part with these two phones, mainly because of lack of space to store my surplus gear, but also because I hope that those vintage items could be preserved in the future. They are now for sale on Ebay https://www.ebay.it/itm/146651083307 but please feel free to send me an email to inquire. My email address is iz5pqt (at) gmail,com.
TF38 #2 (left) and TF38 #1 (right), Both units are missing the crank handle housing which was usually fixed on top of the ringer with two screws (present in #1.)
On the test bench
TF 38#1 (left), TF38 #2 (right)
No maker's name for TF38 #1. Date is 1944. For TF38 #2 K stands for Kammerer and date is 1943.
The circuit diagram label is missing in TF38 #1
The Phonetic Alphabet Table (Buchstabiertabelle)
Below the schematic diagram. Note the three paper capacitors. the numbers represent the color coding of the wires.
The terminal bord is shown below. The first two posts from the left 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 central battery phone lines) or to the fourth post (La/OB/SB for local battery lines). When the line is connected to La/ZB and the handset is on hook capacitor C1 blocks the DC current from the central battery. Lifting the handset skips C1 allowing a DC current to flow through the ringer. The other line wire (or the earth connection) goes to the last post on the right (Lb/E). The large 4-pin socket on top is for the handset plug. There is also a bipolar socket for extra headphones. The screw terminals on the bottom row are for an extension ringer (W2) and for extra earset (F) and microphone (M).
TF38 #1
The chassis. At the rear of the chassis is the induction coil. The multicontact cradle switch is visible on the left photo.
The handset with the PTT button. The cloth covering the cord is a bit frayed but it works perfectly with no intermittent contacts or shorts. The microphone is original. The receiver has been replaced with a "modern" identical type (standardization in Germany was taken seriously.). The issue with the original receivers was the poor quality of the permanent magnets, that quickly lost magnetization.
Front of receiver #1. OLAP was an italian firm owned by Siemens & Halske.
TF38 #2
The bakelite case.
The case front. The K on the tag is the logo of Kammerer Telefonbau, München. The tags also shows the year (1943) and a serial number.
The chassis. At the rear of the chassis is the induction coil. The multicontact cradle switch is visible on the left photo.
The handsets with the PTT button. The cord cloth is a bit frayed but it works perfectly with no intermittent contacts or shorts. The microphone is original, the receiver has been replaced with an equivalent model. The quality of the permanent magnets in the original magnets was poor and they were quickly demagnetized.
The carbon microphone with the WaffenAmt stamp
The plug for TF38 #2 handset lacks a cover but it works ok.
Both phones have been completely rewired since the old insulation (very thin silk) was damaged and developed intermitten shorts. In one sample the C1 capacitor was shorted and was replaced with a new one.
The replaced C1 (left) on TF38 #1.
RESTORING OLD PAPER CAPACITORS
Some of the capacitors after 80 years became leaky. They were restored by substituting modern types, preserving the external appearance, These capacitors were typically of 1 or 2 μF. In this telephone there is also a dual capacitor with two 1 μF units inside the same can (C2 and C3). The can is potted with black tar (see the pictures below) which must be removed. Note that, unlike american "bathtub"capacitors, the cans are not hermetically sealed, which makes restoration simpler.
The terminal board (bakelite) is first removed, exposing the black tar, which is then molten. I used a heavy-duty soldering iron with flat tip. The internal parts are then removed and discarded, A very messy job!
What was inside!
The can interior is cleaned, then two 1 μF replacement plastic capacitors are soldered to the terminal lugs and the terminal board is put back in place. Hot glue keeps the two capacitors together to add some rigidity. Two bakelite rectangles glued to the can sides keep the board flush with the opening. Kerosene (petrolio bianco) can be used to wash away residual tar.
The restored dual capacitor.
Above: a DIN standard new capacitor as used in german phone sets of the 1950s-1960s. It is a direct replacement for the TF38 C1.
Some diagrams useful for repair
