The WR1 is a German radio widely used by the German Army in WW2 as an entertainment receiver, and nicknamed “Rudi”. It had good performance and rugged construction. It was intended for front line use, so had a “universal” power supply. It was not intended for domestic use where mains power was available.

The radio was designed by Blaupunkt in1940, and used Telefunken metal valves. These were civilian valves, and had to be additionally military certified. This radio had the letter “T” stenciled at the top left hand corner of the front panel, so that the appropriate spares could be kept. The nameplate only showed WR1, but the model was generally known as WR1/T. The replacement 1941 model, used new glass valves developed by Philips, using loctal bases, and made by Valvo. Internally within Philips, they were known as “Rudi tubes”. This radio had the letter “P” stenciled at the top left hand corner of the front panel, and the model was generally known as WR1/P. Blaupunkt manufactured about 21,000 WR1/T models and about 4,000 WR1/P models. Philips manufactured about 13,000 WR1/P models.

Picture 1: Front View

The manual is not easy to read, as it is in German, and printed using a Gothic font. The WR1/P manual is dated 4.10.1941. It has a four page supplement, including a frequency chart of all the German radio stations, dated 28 October 1941. It also covers the additional filament batteries and the dropping resistor values. The batteries are 2 volt, 4 volt (14 ohm), 6 volt (28 ohm), 12 volt (75 ohm) with an adapter plate.

The radio is very heavy (26 kilos), as it comes in a wooden transit case with a protective front cover. When fitted with batteries, it is 6 kilos heavier. It was meant to be used anywhere, so the “universal” power supply has a variety of settings. It can run from an AC mains supply of 90-260 volts or a DC mains supply of 90-260 volts. It can also run from internal batteries, one 90 volt DC high tension battery (ANODEN BATTERIE) consuming 30 mA, and two 1.25 volts Nickel Cadmium filament batteries consuming 400 mA. It has no internal aerial but relies on an external long wire. It can also serve as a gramophone amplifier, and for announcements, has a microphone input as well.

It has three wavebands…………
Long wave (LANGE WELLE) 150 – 525 kHz (2000 – 706 m)
Medium wave (MITTEL WELLE) 517 – 1540 kHz (580 – 195 m)
Short wave (KURZ WELLE) 6.0 – 15.5 mHz (50 – 19.4 m)

Alternatively, there could be three other short wave bands fitted…..
KURZ II 21.7 – 10.5 mHz (13.8 – 28.5 m)
KURZ III 10.5 – 4.6 mHz (28.5 – 65 m)
KURZ IV 4.6 – 1.5 mHz (65 – 200 m)

The WR1/P uses glass loctal valves which have a 1.2 volt filament. The valves (RÖRHEN) are a DCH25 mixer/oscillator (hexode, triode), two DF25 IF amplifiers (pentodes), DAC25 detector and audio preamplifier (diode, triode), DC25 audio amplifier (triode), DDD25 push pull power amplifier (double triode), DF26 gramophone amplifier (pentode), OSRAM MS 50 voltage regulator (Glimm lampe), current regulator U 518 H (URDOX), and a selenium half wave rectifier.

Picture 2: Rear View

CONTROLS
The radio has a vertical aspect and has the speaker at the top left, and two battery shelves on the right. The batteries slide in, are secured by leather straps, and are covered by a small door. Below the battery compartments, is a space to stow the headphones and power cord. Above the speaker is a ventilation grill, and below the speaker is the main dial. Near the dial scale is a meter, which is used to set the voltage to the RED coloured safe zone. A press button on the meter shows the high tension voltage reading, which should be in the GREEN zone. Below the meter is the TONE control (TON-BLENDE). Below this is the VOLUME control (LAUT. STARKE), and next to it the TUNING control (ABSTIMMUNG). This is a two speed dial. It has a coarse tuning ratio, and when the station is reached, you turn the knob the other way, and it is has vernier ratio. In the centre at the bottom is the WAVEBAND switch (WELLEMBEREICH) which selects the three frequency ranges and also the gramophone input. To the left are three terminals, the left most is for a microphone input (MIKROPHON) and the right most for the gramophone input (TONABNEHMER). In the middle at the bottom is the nameplate.

At the top right, next to the batteries are the HEADPHONE terminals (KÖPFHORER), and a little window to view the glowing regulator tube. There is a warning plate below this. The main switch is located here, and turns the radio OFF (AUS), or selects BATTERIES (BATT.) when turned anti-clockwise. When turned clock wise, it selects the MAINS supply (NETZ) and there are 12 positions that gradually increase the voltage, until the meter reading is in the small RED area. This is critical as it is the filament voltage. The high tension can be checked by pressing the button on the meter, and it should be in the GREEN area, which is much wider and less critical. There are two preset controls that can be set with a screwdriver. There is a lifting handle between them, that looks like a cupboard or drawer handle. The top preset is for tuning the aerial capacitor for the best match (SPERR KREIS ABSTIMMUNG). The bottom preset is also for aerial matching, and switches in an extra inductor (SPERR KREIS BEREICH). It has two positions labeled (I, II). At the bottom right hand side, are three terminals labeled, earth (GEGENGEWICHT), aerial (ANTENNE), tuned aerial (SPERR KRIES-ANTENNE).

The warning plate says
ACHTUNG!
BEI NETZBETRIEB DIESEN KNOPF
LANGSAM NUR SOWEIT NACH
RECHTS DREHEN BIS INSTRUMENTENZEIGER DIE
ROTE MARKE ERREICHT HAT

Literally……
ATTENTION!
WITH POWER OPERATION THIS BUTTON
SLOWLY TO THE EXTENT PERMITTED BY
TURN RIGHT HAND TO THE INSTRUMENT
RED BRAND HAS REACHED

Which means…..
WITH MAINS OPERATION,
TURN THE KNOB SOWLY
UNTIL THE NEEDLE POINTS TO THE RED AREA

If the radio did not have a meter fitted, then the voltage could be set by watching the voltage regulator through the little window, and adjusting the voltage. When the regulator valve glowed, the voltage was correct.

IMPROVEMENTS
The valves used in the WR1/T model were DCH11, DF11, DAF11, DC11, DDD11, and DAF11 metal valves. The P model used the newer glass loctal valves. Also introduced were five screw fixing, instead of two. The grip for extracting the chassis was improved. A window was provided to view the glowing regulator valve. The ventilator grill was altered. The filament battery could be changed to higher voltage (2 – 12 volt) lead acid type, and a battery heater added.

DIFFERENCES
Some models did not have the meter fitted.

The chassis has an extra valve hole and transformer hole punched, to enable a BFO to be fitted for CW reception. This used a DC25 valve, and a slug tuned transformer. The BFO was injected into the detector. The switch was screwdriver operated and positioned on the front panel between the TONE and VOLUME controls. It was labeled ON-OFF (EIN-AUS) and FEEDBACK (RÜCK-KOPPLUNG).

Figure 1: WR1/P-Rü Circuit

The marine version had the label KRAFTWERST next to the headphone terminals, which provided an output level to drive an external power amplifier.

Figure 2: WR1/P-Mar Circuit

There was another version that had a screwdriver operated audio switch and two terminals, positioned on the front panel between the TONE and VOLUME controls. The terminals provided low level transformer coupled audio output (AUSGANG) from the receiver for an external power amplifier. The switch controlled the input for the WR1 internal audio amplifier, and selected the normal receiver audio (EMPHANGER) or the microphone input. It did not use the microphone amplifier valve. Separating the RF and AF sections of the radio, made the operation more flexible.

Figure 3: WR1/P-Pk Circuit

DESIGN (MECHANICAL)
The radio is roughly divided in half, with the power supply at the top, and the receiver at the bottom. The front panel is heavy gauge steel, and painted grey. It is fitted with engraved labels for the controls.

The power supply occupies half the radio, as it has to cope with a variety of voltages, and battery power and also generate a hum free DC voltage for the filaments. There is no power transformer, but several dropping resistors are used, with taps selected by the voltage switch. At the very top are the mains fuses, chokes, and power resistors. The filter capacitors are beneath them. Some heat is generated when used on mains voltage, so there is a large ventilation grill at the top. There is a single section selenium diode, to rectify the AC mains voltage, a gaseous voltage regulator for the filament voltage, and a barrater for the filament current.

The bottom section has a vertical chassis, that holds the valve sockets, audio transformers, and IF cans. Between this and the front panel, are the RF and oscillator coils, on the RHS and wiring on the LHS. The coils plug in. The band switch is at the bottom. The complicated power supply coupled switches are between the two sections. Both the receiver and the power supply are insulated from the front panel.

The valves are held in place by the loctal socket, and by felt pads in the rear of the wooden box, that press against the valves. Many resistors and capacitors are neatly mounted on insulated boards. Their ends are twisted together and melted, or welded! When wires are attached, they are soldered.

DESIGN (ELECTRICAL)
The radio is a three band super-heterodyne receiver. The RF and IF sections are conventional.

The chassis is floating, as for a normal transformer-less radio, but there is a counterpoise terminal (GEGENGEWICHT) on the front panel, that connects to the chassis through a capacitor. The aerial terminal (ANTENNE) is also connected through another capacitor to three switched aerial coil primaries. There are also three switched secondaries that connect to the mixer grid. Each RF transformer has a coupling capacitor across the top, adding extra coupling. There is a series LC circuit, and also a capacitor to ground, which behave like traps. The other aerial terminal (SPERR KREIS ANTENNE) has three components, a large inductor, a small inductor, and a variable capacitor. These can be selected, depending on the band in use and the aerial length or type. The variable capacitor (SPERR KREIS ABSTIMMUNG) is always in circuit and screwdriver adjusted, but the smaller inductor can be switched in or out (SPERR KREIS BEREICH) literally “lock circuit range”. So the thought put into the aerial matching circuits, is an attempt to match any aerial, of whatever is available or practical. There is no RF amplifier stage.

The mixer is a DCH25 hexode and has AGC on the grid. The valve also contains a triode, serving as the oscillator. There are three oscillator tuned circuits, and each one is switched completely in or out, as both the primary and secondary are switched. The IF amplifier consists of two DF25 pentodes, both with AGC on the grids. There are three IF tuned circuits, all slug tuned, the middle one is just a single coil, but the other two are transformers. The IF frequency is 468 kHz.

The detector and audio preamplifier is a DAC25, which is a diode and triode. The single diode rectifies the IF signal and generates the audio as well as AGC. The volume control feeds the audio to the grid, and it has a tap for a “loudness” control. The audio preamplifier triode, feeds another triode, type DC25, which uses a transformer to drive the audio power amplifier. This is a dual triode, type DDD25, arranged in push pull, which is transformer coupled to the internal speaker. There is a four position tone control, connected across the speaker transformer primary. This selects one of three capacitors, the fourth position has no capacitor, but relies on fixed capacitors across the primary. There is a resistor in each anode lead as well.

There is a terminal on the front panel to allow a gramophone pickup to be connected, and this goes to the volume control. The waveband switch selects this function, connecting the pickup, and disconnects the screen voltage to the IF and mixer valves. It also connects voltage to the filament of a DF26 pentode, which acts as a microphone amplifier, and its output also goes to the volume control. The microphone is connected to the other terminal, though a transformer.

HIGH TENSION POWER SUPPLY
The power supply is complex, so the battery supply will be considered first. The circuit shows the switches in the battery position. When switched to battery, the high tension battery positive connection has a bypass capacitor, then goes through a fuse to power the radio. The press button on the meter, when pushed, measures this voltage. The battery negative lead, goes through a bias network, which provides negative voltage for the power output valve, and through a diode for the audio amplifier, and also to the AGC line.

When switched to mains operation, the power input has a switch contact, fuse, choke and bypass capacitor on each line. One mains lead goes to two multi-tapped power resistors in series, and the voltage switch selects one of nine taps on them. This then goes to the selenium rectifier, and a capacitor choke combination, to generate the positive high tension. This replaces the battery voltage. The other mains lead is the power supply negative, and this connects to the negative of the battery, and through the bias network, but with an extra resistor switched into circuit.

LOW TENSION POWER SUPPLY
The circuit shows the switches in the battery position. The filaments are arranged in two circuits, and powered by two 1.2 volt batteries in series. The valves are shared on the two circuits. All the valves are powered while the radio is on, except the microphone amplifier, which is only on when needed. The centre connection of the two batteries goes to chassis. The meter shows the total battery voltage, that is, both batteries in series.

When switched to mains operation, the filament batteries are switched out of circuit, and two 50 ohm resistors are switched across each filament circuit. The meter circuit is switched to a different measurement point. The rectified voltage from the selenium diode, goes through another multi-tapped power resistor with 5 taps, and goes to a 65-75 volt gas regulator (Osram MS 50). This then goes to a 180 mA barrater current regulator (Urdox U 518 H) and to two smoothing chokes and two filter capacitors. It connects to the filaments and the meter.

Picture 3: Regulator valves

There is a relay in the voltage regulator cathode, which removes the mains input if the current is too high. There is a relay across the mains input, that operates if the mains voltage is too high. The voltage select switch is very complicated and is actually three switches, operating together. One switch selects Batteries, Off, or Mains, and the other switch selects all the voltage taps. There is a mains toggle switch as well. They are all mechanically connected together and operated by only one knob.

Picture 4: Power Switch

RESTORATION
The top ventilator had been removed with a hacksaw, and the radio was full of metal fillings, and some dead spiders. There was also plenty of dust. An extensive cleaning operation was performed, and a magnet used to remove all the metal particles, particularly from around the speaker. The speaker was removed, cleaned and tested. The cloth bag over the speaker had protected it to a large extent.

Picture 5: Metal Filings, Dust and Spider

Several large wire wound resistors, had broken clamps and taps, and the wire had un-spooled and become a tangled mess. New clamps and taps were made, and the wire rewound and fixed in place. The values were checked against the circuit.

Picture 6: Wire Wound Resistors

The radio chassis was cleaned, and some rusty areas were protected. A broken valve socket was glued back together. Two carbon resistors were broken, and were replaced with new ones, which were a close physical match.

The filament dropping resistor for the microphone amplifier, had a 50 ohm resistor fitted. The circuit said it should be 25 ohms. It was physically broken and needed replacing. I checked with a replacment 50 ohm resistor and it gave almost the correct voltage. The WR1/P-Rü circuit shows a 40 ohm resistor.

The front panel was extensively scratched, and also had a name scratched into the front. It needed repainting. The ventilator grill was missing, and some photographs showed a square grill, and other photographs showed a sloping grill. A new front panel was found, and it had the square grill, but also had the sloping grill on the back. It was painted the correct grey colour. A stencil was made and a “P” was stenciled on the front. The dial cover had shrunk, was dis-coloured, and was loose in the bezel. It had also warped and the dial pointer had scratched it. A new cover was made from thick clear plastic. The dial was scanned on a computer, and the letters and numbers repaired pixel by pixel. The scratches were removed. A colour decal was printed in reverse, so that it could be affixed to the inside of the dial cover. The wooden case was in good condition, but had plenty of scratches, so it was left as it was.

Two of the valves were missing, the DAC25 was easy to locate. The DCH25 mixer was difficult to find, but with the help of a friend, one was eventually located. The selenium rectifier was also missing, so I assumed it had failed and been removed. During a visit to the Friedrichshafen Ham Radio meeting in June 2013, an identical replacement was found in a junk box. It proved to be 115 k ohms in both directions, a rather poor front to back ratio for a diode, so it was fitted to give the correct look, and a 1N4007 silicon diode was hidden behind it.

The IF was aligned to 468 kHz. The bottom slug in the two IF transformers cannot be reached from the rear of the chassis. The top slug has a large hole in it. It is so large, that a long plastic screwdriver can reach through the top slug, and engage in the bottom slug. So both slugs can be adjusted from the top side of the chassis. It was a long way off tune, and aligned nicely.

Figure 4: Circuit WR1/PFig4_WR1P_cct

Figure 5: Circuit WR1/T

CONCLUSIONS
The radio is a horrible mechanical design, using many pressed steel panels and brackets. Many components are difficult to access and replace. A more logical and simple design would make construction easier, and servicing better. It is not as rugged as a military designed radio. An RF amplifier would help, and the audio section could be simplified if two pentodes were used instead of three triodes. The controls are simple. The aerial matching circuits are good. The plug in coils are a good design. Valve access is easy. The lack of a BFO is normal for an entertainment receiver, but it has provision for it, if one is required. The wooden box provides good protection. The universal power supply will suit all areas, and can even be used in arctic climates.

Picture 7: Photo of Field Use (Courtesy of Helge Fyse)

REFERENCES
Manual, Wehrmacht Rundfunkemphangers 1, WR1/P, D1029/1, 1/7/43
Manual, Wehrmacht Rundfunkemphangers, WR1/P, D1029/6, 4/10/41
Museums Bote, Des Ersten Osterreichishen Funk – und Radiomuseums, Nr 132, Nov –Dec 2005, Werner Thote, Radeberg.
RKK Radio museum, exhibit 431 and 463

OTHER VIEWS

Picture 8: Left Hand Side

Picture 9: Right Hand Side

Picture 10: Front Panel Removed

Picture 11: Top

Picture 12: Bottom

Copyright
Ray Robinson vk2no

INDEX