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The 15W.S.E.b is one of my favorite Wehrmacht transceivers. It's relatively complex, powerful and is one of the few devices built to operate with the Feldfernschreiber.

When I received this unit, I knew that no one had touched it since 1943. There was a thick layer of dirt on it and the plexiglass on the frequency readout window was cracked. Cleaning the dirt off with soap and water revealed a nice original paint finish with a small amount of oxidation to the face-plate. The oxidation was immediately halted with silicon spray solution (lubricant), applied where needed on the face plate.

After taking the device out of the cover, I noticed it was in excellent and untouched condition. The trimmer covers were all intact - a sight not often seen on these units. This means no one messed with it after the war.

My next step was to replace the plexiglass covering the frequency window. Thinking it could have been accessed from the front, I unscrewed the four retaining screws, only to watch the old window drop down behind the face-plate. I then had to remove the faceplate, make a new plexiglass window, and install it. (Page 1)

My next step was to inspect the unit visually, to check if there were any visible problems with the components. Since the unit was not taken out of its case since the end of the war, the components were sealed inside and looked good.

A note about the 15 W.S.E.b

Bei den Geräten ab Nr. 067410 ist das Bremsgitter der Röhre Rö 1 nicht an Potential 17 (Anode), sondern an Potential 0 (Masse) angeschlossen.

Warning! On all transceivers with a serial number larger than 067410, the suppressor grid on vacuum tube 1 is not connected to the anode (Potential 17), it is connected to ground (Potential 0).


Lower cover removed. At first glance, everything looks good. Very interesting that each solder joint has pink lacquer on it. Just like the Soviet R-123.



Transmitter modulator section.



Second heterodyne stage.



Ü3 (transformer 3)



Drossel 8



On the top left is the low-frequency (audio) amplifier tube with related components. On the top right is the 2nd heterodyne, and below is the transmitter modulator section.



Interesting stamp below one of the variable tuning capacitor bulkheads "Temperiert" or tempered.



One of the several terminal boards in the unit. All screws were removed and contacts cleaned.



The 15W.S.E.b after additional cleanup. The original paint really looks great now. On the lower right is the new power cable that I made with an original connector. There are 9 wires in the cable.



Here is the original connector.



Photo of the male socket.



Power Connection Guide for 15W.S.E.b


Male socket numbers Female connector numbers Purpose Elect. properties My wire colors
0 9 - H receiver & -H transmitter
- A transmitter
Ground Green
1 6 + H transmitter +4.8 V (2.6 A) Blue
4 8 + H receiver +2.4 V (0.6 A) Red
12 5 + A transmitter +320 V (140-200mA)* Orange
30 4 + A receiver +90 V (10 mA) White
72 2 - A receiver -90 V Black
145 7 + voltage for microphone & relay R1 (key and telephone)* +2.4 V* (triggered at 1.2 volts) Yellow
163 3 + relay voltage for activating Ewe. or (E)f1 vibrating power supples +12 V Brown
Empty 1 NA NA NA


* Microphone relay voltage must be connected to ground or telegraph key be activated (see schematic: Bu1, Bu5 -> U4 -> R1)

This data was gathered from the LA8AK site.



The 15W.S.E.b uses ALL of my rack-mounted power supplies. Minuses (-) for -H receiver, -H transmitter, -A transmitter connected to each other AND to ground.



When testing the transmitter anode voltage, the microphone relay connector must be bridged to ground to create a circuit through the relay. This is equivalent to the radio operator activating the PTT button.



The yellow wire is connected to terminal #7 (relay voltage). Here the minus (-) is connected to ground and together they are connected to the common ground with the black wire. The voltage shown is about 1.7 volts DC. The relay triggered at around 1.2 volts. Since there is no documentation in both my manuals about the actual relay voltage, it can be assumed that it uses the 2.4 filament volts for the receiver.



Measuring at the tube sockets.



At the power supply. There are no tubes, but there is still some current draw (around 1 A) - will have to find the cause of this.



The 15W.S.E.b voltmeter reading - looks good.



2.4 Volts for the receiver filament power.



Reading at the tube sockets.



The 15W.S.E.b voltmeter reading - looks good.



Now the relay is activated to simulate the PTT microphone button or the telegraph key being pressed. This is an energy-saving feature of this transceiver.



280 Volts. The specifications of the 15W.S.E.b state 320 volts for the transmitter anode, but 280 is just fine.



Reading at the tube socket.



The 15W.S.E.b voltmeter reading - the arrow is just shy of being in the blue sector in the 'Sender' region because of the reduced voltage.



100 volts of anode power for the receiver.



Reading at the tube socket.



The 15W.S.E.b voltmeter reading - looks good.




All new tubes arrived. All tubes tested excellent on the RPG 4-3. Inserted the tubes, turned on the receiver - no sound. First problem discovered was the LF stage was not receiving a signal from the detector. Passing a 5000 Hz signal from the anode of the detector did not not register any sound. Applying the same signal to the anode of the LF tube socket registered a clear tone on the speaker. Next step is to troubleshoot the the detector stage. The problem turned out to be a bad tube in the LF stage. It was replaced and the following results were obtained:


Input Signal Sensitivity Frequency Scale Set To
3000 kHz 10 µV 3020 kHz
3900 kHz 3 µV 3920 kHz
4800 KHz 10 µV 4830 kHz
4700 kHz 30 µV 4710 kHz
6100 kHz 30 µV 6110 kHz
7500 kHz 30 µV 7515 kHz


Each frequency range was measured at the bottom, the middle and at the top of the range. The antenna tuning control was adjusted accordingly to attain maximum performance at each measurement point. The input signal was 5000 Hz with 50% modulation.

It is clear that both frequency ranges have drifted. The first range drifted +20 kHz and the second range drifted +10 to +15 kHz. This is very very good for a radio receiver which has not operated since the 40s or 50s. The upper frequency range is also less sensitive than the lower, and this may be the result of being de-tuned. Next step is to tune the 15 W.S.E.b




Tuning Procedure

(as translated from D 1025/6)


VII. Makeshift Frequency Testing

(reproduced here from D 979/8 "Pamphlet about the tuning of transceivers")

Frequency testing and tuning is necessary

1. When frequency deviation is noticed,
2. After replacing vacuum tubes, especially the oscillator tube of the transmitter and the first heterodyne (local oscillator) tube of the receiver,
3. After a major repair.

For frequency testing with the test device SE 15 b refer to D 9011/5, "Pamphlet for operating the test device SE 15 b".
If an SE 15 b is not available, makeshift frequency testing may be performed with the 15W.S.E.a or the Frequency measurement device a.

On the 15W.S.E.b, remove the transceiver from its case, and prepare it for operation but without the antenna or ground connection. Connect the telegraph key and headphones. Attach the Dummy Load 15 to the antenna connection "A" and ground protrusion "G". Set the mode selector switch to "Senden / Empfang Tg" and set the indicator of the "Empfänger=Nachstimmung" to the "O" position.

Makeshift Frequency Testing with the 15W.S.E.a

Configure the 15W.S.E.a (refer to D 1025/5) with the dummy load antenna 15 a, telegraph key and headphones. Position the 15W.S.E.a approximately 4 meters from a 15W.S.E.b (test subject) which is ready to operate. In small radio detachments "f" (motorized) (kleinen Funktrupp f) the devices will be in vehicles, then drive apart to reach the necessary distance.
For testing the transmitter by using the 15W.S.E.a as the test receiver, configure it as a test transmitter for receiver testing. On the 15W.S.E.a, set the mode switch to "Frequenzprüfung" (Frequency Testing) and the indicator knob "Empfänger=Nachstimmung" to the "O" position.

Use the following frequencies:

In frequency range I 4500 kHz (blue point) and 3000 kHz (blue sector), in frequency range II 6750 kHz (blue point) and 5250 kHz (blue sector). Test frequency first on the scale, then follow the below instructions exactly:



Test Device SE 15

A. Introduction

The test device SE 15 b serves for the frequency testing of the 15W.S.E.b and operates from the same power source as the transceiver.

Weight of the test device SE 15 b: 1,93 kg.

B. Technical Construction

I. Outer construction (illustrations 12 and 13)

The test device is comprised of:
a) the tester SE 15 b with one vacuum tube RV2,4P700 and one quartz of 750 kHz,
b) a power connection cable to feed off the transceiver's power supply (illustrations 14 and 15),
c) a 90 cm long antenna cable with one single male banana plug 4 mm in diameter for coupling with the transceiver,
d) A wooden box for containing items a-c.

II. Internal construction of the tester SE 15 b (illustration 16)

The control grid circuit of the tube RV2,4P700 is in a triode configuration. The oscillator quartz Q2 is connected in parallel with resistor W3 in the anode circuit as an oscillator. The inductor L4 together with the trimmer capacitor C5 establish the natural frequency of 750 kHz that the quartz is configured for. Over the capacitor C6 reach the high frequency oscillations onto the cathode of the tube RV2,4P700. The anode circuit is connected to the primary winding of the low-frequency transformer Ü8, which is bridged through the cathode with capacitor C7, and the secondary winding connected to the headphone jacks T. The antenna cable, and power connections for -H, -A, +H, +A are connected through the capacitor C6.
The tester SE15b represents a crystal-controlled transmitter that does not just oscillate at the natural frequency of its crystal, but also on the multiples of the fundamental frequency. This is how the 15W.S.E.b can be tested at the 3000, 4500, 5250 and 6750 kHz.

Frequency testing of the transmitter: The high frequency oscillations of the transmitter (test frequencies) come from the dummy load antenna over the antenna cable onto the control grid of the tube RV2,4P700 of the tester and overlap with it's own oscillations. The overlap tone is heard through transformer Ü8 and through the headphones

Frequency testing of the receiver: The high frequency oscillations of the tester occur over the antenna cable and dummy load antenna and respectively over the power cable of the receiver. The detector oscillates by itself in the mode of "Tg", and overlays itself onto the testing frequencies. The overlay tone is heard through the headphones when connected to the the transceiver.

C. Testing the 15W.S.E.b with the Test Device SE 15 b (instructions)

Frequency testing and tuning of the 15W.S.E.b is necessary when:

    1. When frequency deviates during use.
    2. After replacing tubes, especially the transmitter oscillator RL4,8P15 and the 1st heterodyne tube RV2,4P700 of the receiver.
    3. After a major repair job.

I. Preparing the device (Photos 14 and 15)

1. Take the 15W.S.E.b out of its enclosure by unscrewing the four bolts that hold them together. Attach the dummy load antenna 15a, and attach the connection cable from the test device SE15b to the transceiver and a power source (Photos 3 and 4). Connect the antenna cable to the test device. Loosely overlay the antenna cable over the dummy load antenna. Switch the mode of the 15W.S.E.b to "Senden/Empfang, Tg" (transmit/receive, telegraphy). Wait about 5 minutes until the whole configuration has thoroughly warmed up.




II. Testing the frequency of the transmitter (Photo 14)

Connect the headphones to the test device SE15b.
Tune the device to exactly 4500 kHz (blue point). Depress the key and adjust the dummy load antenna to its maximum current setting. With the key depressed, adjust the trimmer on the right side of the transceiver ("Frequenzprüfung-Sender, Bereich I") with a screwdriver so that the local oscillator's tone is of maximum volume. Now set the frequency to 3000 kHz and tune the antenna again. The 'beat gap' of the occurring oscillator tone must lay inside the blue sectors of the scale. If not, the transceiver is very misconfigured and must be sent away for a deeper repair.
Next, frequency testing of frequency range II is performed at 6750 kHz (blue point) and cross-checked with the frequency of 5250 kHz (blue sector) in is made in a similar way with the tuning trimmer "Bereich II".

III. Frequency testing of the receiver (Photo 15)

Connect the headphones to the transceiver, set the indicator knob "Empfänger=Nachstimmung" to the "O" position.
Although the frequency testing is similar to section II, use the trimmers marked "Frequenzprüfung-Empfänger", "Bereich I" and "Bereich II" on the left side. Set the volume to an audible level.
When frequency-testing the receiver, leave the key circuit open. However, before each setup of the test frequencies, tune the antenna by using the transmitter as described in section II.

IV. Makeshift frequency testing of the 15W.S.E.b with the 15W.S.E.a and Frquenzmeßgerät a

Refer to D 1025/6, "Pamphlet for the operation of the 15W.S.E.b".


This is what's visible after removing the the cover marked "Frequenzprüfung-Empfänger / Bereich I Bereich II". Although I could rotate trimmer C53 with some difficulty using my fingers, trimmer C51 would not budge. So finally, I used my "patented" trimmer loosening tool to make it move. Remember NEVER use a screwdriver on these types of trimmers. Always either use your fingers or my tool shown below. Never use pliers tweezers or any other metallic tool on these trimmers - as they WILL break.



After tuning the trimmers for both frequency ranges, the results are indicated in the table below. This is much better performance.



Input Signal Sensitivity Frequency Scale Set To
3000 kHz 3 µV 3005 kHz
3900 kHz 3 µV 3900 kHz
4800 KHz 3 µV 4800 kHz
4700 kHz 3 µV 4700 kHz
6100 kHz 5 µV 6100 kHz
7500 kHz 5 µV 7500 kHz

Transmitter Repair


When tested, the transmitter was dead. There was no output from both of the final stage tubes. There was also no signal generated from the carrier wave generator (local oscillator). Turns out there was no voltage between the screen grid and ground. After testing the components of the oscillator screen grid circuit, I found that resistor W2 (large black one in the photo was completely dead (open line across it). After installinganother equivalent resistor, the generator started to provide a carrier signal again.



Then I could proceed with tuning the transmitter on both frequency ranges. C13 and C15 above were used to tune Bereich 1 and Bereich 2 respectively.



Untuned frequency generated by the transmitter's oscillator

(attenuation = 50 dB, bandwidth = 30 kHz, scan/division = 100 kHz, center frequency = 3 MHz)