Oliver Archut wrote on Thu, 16 December 2004 05:13 |
[...]the "locked stock" was released for final testing (the test circuit was developed by 'Schalltechnik', better known today as Schoeps.) |
Quote: |
here is some empirical data, from my 20-year experience with the tube: 1. Two out of three non-Neumann select AC701s (non-k) are not usable in microphones: they will have steady-state white noise or irregular discharges, beyond an acceptable level for critical recording situations. 2. One out of three non-Neumann select k are unusable, for the same reason. 3. One in 10 Neumann-select (in Neumann-box, with Neumann serial number on paper band around tube) are unusable. 4. Never judge an AC701 before at least a 48hr. burn-in (i.e. the tube is installed in the mic for which it is intended, and voltage-adjusted to the proper operating voltages): One in three tubes which were fine within the first hour of testing will develop discharges later on, especially once the tube has reached its thermal stability ( thermal stability = operating temperature of the tube, once the tube's heat dissipation through the heat sinking around it has stabilized, and the tube and its surroundings won't get any hotter). 5. Unlike tubes which you plug in, you cannot easily and thoroughly test an AC701 for noise outside of the mic, for example, with a tube tester. This tube needs to be soldered into the mic for testing. 6. Unfortunately, you rarely will be able to return AC701 tubes once you have installed them because the seller cannot easily sell an AC701 to the next customer as new, because its filament wires have already been cut and twisted for installation. This is especially true for Neumann KM-series. |