TELEFUNKEN V-69a, F2a11 PP , 1952The Telefunken V-69 is an interesting amplifier of stringent symmetric design. The Telefunken V69 series is a typical German design of studio audio amplifiers made from the late 1940’s up to the 1960’s. Lots of such German amplifiers made use of the balanced phase inverter types, and very often so, to act as the driver as well. A thing that often puzzles me with regards to Western Electric designs and other push pull designs equipped with input transformers, is that this very input transformer is followed by some sort of electronic phase inverter. If you insist on an input transformer, why not use it as the phase splitter as well ? All we need is a centre tap. Telefunken were obviously thinking in the same terms and here the input transformer does indeed handle the phase splitting. Excellent….UPDATE: Due to a mail from Frank Blöhbaum, Germany, I have momentary withdrawn a large part of the vignette covering the V69a Amplifier. Frank Blöhbaum correctly pointed out that my analysis with regards to the feedback scheme was wrong. I apology for this mistake. It turned out I had made an incorrect drawing in my notes and was actually partly analysing the “wrong” amplifier.Thanks a lot to Frank Blöhbaum for spotting the mistake. I will upload the material again, once I have corrected it for the error.The EZ12 rectifier is an indirectly type developed by Telefunken and introduced in 1938. Although the Telefunken datasheets recommends the use of series resistors it was hardly mandatory as Telefunken themselves ignores that advice in the V69. EZ12 was the predecessor for GZ34 that came in 1954. Note that EZ12 uses German steel socket and 6,3V heater.EF804s is a special quality, low microphonic, low hum, long life, high reliability, tight tolerance, vibration shock proof, non interface cathode , – pentode…..phew…designed for LF applications. Socket is noval. It is vital for this valve that the heater voltage is kept as close to 6,3 volts as possible. I would apply regulated DC voltage – LM317 or similar. EF804s was a common used pentode in German sound studio and broadcast equipment.F2a11 is one of the best tetrodes developed for audio. A pair will easily provide you with 30-40 Watts in to a 5kΩ load. It is amazingly linear as a triode as well , some 20 Watt’s into the same output transformer. A single one may deliver some 5 Watts with less than 350V at the plate.V-69 was made in three versions. The last model V69b used efficient solid state diodes and swapped the loop bias into conventional active bias. The higher Voltage and lower regulation due to the solid state diodes increased the output power to 35 Watt’s and improved the distortion figures.Not more to say about the Telefunken V69 for now. A less known, but very similar design was used in the German ARD V44 introduced in the late 1940’s.
TELEFUNKEN V-69a, F2a11 PP , 1952The Telefunken V-69 is an interesting amplifier of stringent symmetric design. The Telefunken V69 series is a typical German design of studio audio amplifiers made from the late 1940’s up to the 1960’s. Lots of such German amplifiers made use of the balanced phase inverter types, and very often so, to act as the driver as well. A thing that often puzzles me with regards to Western Electric designs and other push pull designs equipped with input transformers, is that this very input transformer is followed by some sort of electronic phase inverter. If you insist on an input transformer, why not use it as the phase splitter as well ? All we need is a centre tap. Telefunken were obviously thinking in the same terms and here the input transformer does indeed handle the phase splitting. Excellent….UPDATE: Due to a mail from Frank Blöhbaum, Germany, I have momentary withdrawn a large part of the vignette covering the V69a Amplifier. Frank Blöhbaum correctly pointed out that my analysis with regards to the feedback scheme was wrong. I apology for this mistake. It turned out I had made an incorrect drawing in my notes and was actually partly analysing the “wrong” amplifier.Thanks a lot to Frank Blöhbaum for spotting the mistake. I will upload the material again, once I have corrected it for the error.The EZ12 rectifier is an indirectly type developed by Telefunken and introduced in 1938. Although the Telefunken datasheets recommends the use of series resistors it was hardly mandatory as Telefunken themselves ignores that advice in the V69. EZ12 was the predecessor for GZ34 that came in 1954. Note that EZ12 uses German steel socket and 6,3V heater.EF804s is a special quality, low microphonic, low hum, long life, high reliability, tight tolerance, vibration shock proof, non interface cathode , – pentode…..phew…designed for LF applications. Socket is noval. It is vital for this valve that the heater voltage is kept as close to 6,3 volts as possible. I would apply regulated DC voltage – LM317 or similar. EF804s was a common used pentode in German sound studio and broadcast equipment.F2a11 is one of the best tetrodes developed for audio. A pair will easily provide you with 30-40 Watts in to a 5kΩ load. It is amazingly linear as a triode as well , some 20 Watt’s into the same output transformer. A single one may deliver some 5 Watts with less than 350V at the plate.V-69 was made in three versions. The last model V69b used efficient solid state diodes and swapped the loop bias into conventional active bias. The higher Voltage and lower regulation due to the solid state diodes increased the output power to 35 Watt’s and improved the distortion figures.Not more to say about the Telefunken V69 for now. A less known, but very similar design was used in the German ARD V44 introduced in the late 1940’s.<br>
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