I bought this radio from a friend. The case looked nice and stylish, but a bit scratched and a few small pieces of veneer had come off. My friend told me the rectifier had a broken heater, so I thought it would be an easy repair.
After replacing the electrolytics, I tried the radio. No sound at all. When I checked the output transformer, it turned out to have an interrupted primary winding. I looked at the schematic and saw a possible explanation: the terminals for an external loudspeaker on this radio are connected to the primary of the output transformer, not to the secondary. This means things go wrong if you connect a low-impedance speaker or accidentally short one of the loudspeaker terminals to ground. I found a suitable replacement transformer, though I was not sure of the impedance. It turned out to work, but the sound was distorted and the supply voltage was low. After 5 minutes, one of the HF filter capacitors across the HV winding overheated and started sizzling. I turned quickly off the radio and hoped the power transformer would not be damaged. For the moment I decided to do without the HF filter capacitors and tried the radio without them.
I measured the current through the output valve, which was about 100&nsp;mA. This meant he vale had ample emission, which is good, and the coupling capacitor from the AF pre-amplifier was leaky, which is bad. I measured only 2 MΩ resistance. I checked a number of other capacitors, and these were very leaky, too. Actually, testing with my HV power supply set to 250 V, the total of the leakage currents was 3 mA. So I decided to replace most of the paper capacitors. Fortunately, these RFT capacitors are relatively easy to fix invisibly: they are encased in a glass tube, sealed with pitch. I heated the pitch with a soldering iron, pull the old capacitor out and fit a polyesther capacitor in. Because all of the paper capacitors were 500 V types, I used 500 or 630 V polyesther capacitors.
The loudspeaker is a type with a field coil instead of a permanent magnet. This field coil is also used as the power supply choke. I temporarily replaced the choke with a spare choke to be able to test the chassis outside the case without having the the clumsy loudspeaker and baffle on my workbench. When I turned on the radio I was surprised to see the supply voltage rise to a staggering 480 V, to drop to 320 V after warming up, which was still quite high. I realised this was not the intended plate voltage, the loudspeaker would cause a 100 V voltage drop because its field coil has a resistance of 1500 Ω. That is much more than the resistance of the choke I was using. Now I understood why all the capacitors had such a high voltage rating! The power transformer delivers a higher voltage to compensate for the voltage drop across the loudspeaker's field coil. All the capacitors must be able to withstand the 20 second voltage surge at startup, that's why they are 450V and 500V types.
The radio was playing again, though not very impressively. Om MW, I received a few stations in the 500 kHz range, and hardly any at higher frequencies. I decided to realign the coils.
The general condition of the valves is quite good actually, as can be seen on the photograph of the EM11 tuning indicator, which is still very bright.