Nr. 35870

This receiver was manufactured in 1944, therefore one can expect inferior components and materials. The solder is usually of inferior quality, but is still better than the electro-fusion that took place in 1945. As were most post 1941 Ukw.E.e receivers, this one was a "Gelbstrichgerät", or "yellow-stripe device" with allowed it to be used through an intercom box without assistance of a power amplifier, since it used the detector as an amplifier circuit.

The restoration process is described below:




The receiver's face-plate. It has been cosmetically restored before I started working with it.



Someone soldered an ugly tantalum capacitor to compensate for the bad existing one in the audio output stage.



Also there was a disconnected solder joint from a capacitor in the power input circuit. All these silver box paper capacitors are bad and need to be "restored". They open quite easily and allow for a new small capacitor to be installed without much problem and are disguised very well.

The RV12P4000 tubes tested out very well (almost new) on the RPG 3/4, and the receiver worked very well, until Jacques came in to look at it. The reception sound faded to almost nothing over the course of 30 minutes, after which the receiver would not even turn on. The first problem was with the power switch. I had to take it apart. These power switches are meant to be disposable - throwaway, but since I don't have a Wehrmacht supply depot around the corner, I had to salvage this one.




Rear of the power and volume switch where the contacts burned out



The power switch, and the volume control potentiometer are connected together in one structure. Above you can see the power switch mechanism. When the power switch is turned on, the plastic lever arm snaps to the left, and two small rivets create contact with the four paddles on each side of the plastic plate.



The problem was, that one of the rivets burned a big hole in the plastic lever arm. This happened because of age, dirt, and therefore higher resistance of this rivet which generated heat. We had no choice but to make another plastic arm and insert another rivet into it.



Here's what the on/off switch looks like without the plastic arm. Notice the rainbow discolorations on one of the arms, this is due to extreme heat from the electric arcing.



After the switch was repaired, the receiver still lost about 90% of its volume. I started checking all capacitors for their values and for leaks. I found dozens of leaky capacitors, and ones that did not reflect their values. There were several resistors that also turned out bad. The mica capacitors were ok. The above photo shows a restored capacitor in the detector stage.



Here is a completely melted capacitor around the tank circuit of the second IF amplification stage. I call these caps "Tootsie Roll" capacitors for obvious reasons.



Here is a restored audio-output transformer capacitor.



I've now narrowed down the source of the problem to the 1st IF amplification stage. It was not easy, but I finally got to the toughest portion of the receiver.



The gutted HF amplification stage, ready for component testing and restoration.



Testing the coupling capacitor for leakage (it leaked).



Both 1st IF stage capacitors are restored here.



I narrowed down the cause of signal loss to the 1st IF amplification stage. The loss occurred immediately after the trimmer capacitor in the tank circuit of that stage. Since all components either test out good or were replaced with new ones in this stage, I just re-soldered the connections of the 2nd induction coil of the 1st IF stage, and the receiver roared to life!!!

It did not need much tuning after this, as it was already tuned from my first working with it.