Note: This text is a summary of the content of the original German documents
The transistor radio was a sensational German invention. The first transistor radio in the world was made in February 1948 by Robert Denk, a Sudeten German refugee, in Witzenhausen near Kassel (Germany) in refugee barracks. The circuit, a single-tuned receiver, essentially consisted of a pass-band capacitor with a coil, a selenium dry rectifier, a transformer and an electrolyte capacity. The main element was a cylindrical aluminium casing, which housed an electrode made of a silver alloy, which was covered by a oxide coating, a central section between a detector crystal and a radio tube. This was the first radio that worked as soon as it was switched on. The operating voltage was 13 V. The reception range was phenomenal, the selectivity excellent and the sound quality superb. However, it did need a good mains filter. The volume was very high even with low input power. The electrode had a very long service life. As a result of the simplicity of the design, any tube radio could be converted into a tubeless radio.
Originally Denk did not want his invention, the cold cathode, to become public knowledge since he was afraid of an "attack" by the radio tube factories and other interested parties. Work was being carried out in many places around the world on the problem of the tubeless radio and palpable success then forced the inventor to disclose his secret after all, so that the truth could come out that the first tubeless radio in the world was built in February 1948 in Witzenhausen on the River Werra in Germany. Although it is possible that tests in this field being conducted at the same time in other parts of the world had reached a similar stage, the electrician Robert Denk can still claim to be the inventor of the tubeless radio.
This ground-breaking invention came about when Denk made a sensational discovery from a bad contact in 1942. Two exposed and oxidised wires meant that the radio continued to work although two tubes had been switched off. From this time he did not rest until he had completed his invention, until, after 400 failed attempts, he finally hit the nail on the head. It was not until after he fled his home that he was able to analyse the results. The actual tests were started in November 1947 when Denk had to flee from Sudetenland and, after wandering aimlessly, finally found refuge in Witzenhausen. Robert Denk told everybody that he never imagined that he could earn money from his invention whilst he was conducting his tests, but necessity then forced him to apply for the patent.
When the press informed the world's population about the invention of the tubeless radio in November 1948, Robert Denk, who was 32 years of age at the time, was suddenly thrust into the spotlight of public interest. He had managed to achieve what the world of science had failed to do for years. This invention could have resulted in the total and radical change of the whole radio industry. But it did not. At the start of 1949, Denk completed a further development of his invention, a tubeless radio for three wavebands that he was able to hold in his hand and demonstrate before the critical eyes of the radio world. At this time many people both within Germany and throughout the world were attracted by Denk's invention. Denk was unable to withstand all this interest and his health suffered. He wanted to gain time and consider his options in peace. In his despair he destroyed the only existing model so that it could not be stolen. Perhaps it would have been best if Denk had accepted one of the offers made to him from America. But he did not want to do that at any price, he wanted the invention to stay in Germany. Finally he fell into the hands of an irresponsible chancer. The company with which Denk finally signed a contract, told him a short time later that it would have to stop its payments, "since his invention did not work". It dropped Denk gradually until it became insolvent after the discovery of this fraud. Although Denk later destroyed all the documents, it is clear that the radio worked perfectly. Scientific report have also confirmed this. Nobody was able to help him get over this desperate disappointment, however. In the early morning of 19 December 1950 Robert Denk disappeared without trace from his home. He left a letter to his wife in which he said that he intended to take his life and a letter to the authorities in which he asked them to look after his family. On Christmas Day 1950, he returned to his family. From this time the inventor of the tubeless radio went downhill fast. The hopelessness and despair about his fate finally drove him to take his last terrible step. On 12 February 1953 he was found hanged in the old refugee barracks. Later the barracks were demolished as part of an eyesore removal programme. Perhaps this story once again illustrates the tragedy of the inventor who sank into poverty and obscurity whilst others exploited his work for their own good.