Neumann.Berlin U48 User's Manual
Contents
1. Conversion of Neumann U 47 and U 48 microphones to nuvistor tubes nuvistor 13 CW 4 instead of tube VF 14 U 47 960 02 01 In view of the fact that Telefunken quite some time ago discontinued manufacture of the VF 14 tube used in the U 47 and U 48 microphones Neumann has devised a means of converting these microphones from the VF 14 tube to another tube Due to the fact that no completely equivalent tube is available on today s market the following changes have to be made 1 Remove VF 14 2 Remove the leads red blue yellow green black from the tube holder at U 48 remove also 29 Q resistor Remove the tube holder after unscrewing six screws in the three bars Two of the three plastic holders supplied have to be inserted into the screw holes Put the AR 47 upside down into these holders and fix it by inserting the third plastic holder The AR 47 side with three soldering points shows towards the front of the microphone 6 Resolder the leads according to the sketch below at U 48 resolder also the 29 Q resistor 7 Insert nuvistor 13 CW 4 into the socket The NG pwer supply must have a small change of wiring due to the greater heater current required by the nuvistor a Replace resistor R 2 1 kQ power resistor coming from terminal of rectifier by a solid wire connection between the first two electrolytic capacitors b Install this same R 2 in parallel with R 3 an identical resistor next in the RC f2. ilter chain thereby making its total resistance value 500 Q After conversion the U 47 U 48 microphone will have an output level 2 3 dB lower than previously Due to the very high output level of these microphones this is of no dis advantage Should you now have some microphones converted and others unconverted the power supplies and microphones must be marked to prevent confusion ELECTROACUSTIC 12BERLIN 61 WEST GEORG NEUMANN GMBH 427 June 68 Printed in Germany U 47 960 02 01 Should you desire complete interchangeability of converted and unconverted microphones you may wish to do the following a Convert all your power supplies as described above b Install in those U 47 U 48 microphones still equipped with the VF 14 tubes a 1500 2 3W resistor directly at the back of pin 5 B terminal of the micro phone base connector in series with the red lead c Remove this resistor at any time that you subsequently convert to the nuvistor adapter in these microphones NG power supply schematic before conversion after conversion Auf die Lotanschlisse gesehen vorn Soldering side view front gn grn nur bei U48 for U48 only rt red ge yel
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