| Re: Telefunken AC 701 Tube Primer [message #229110 is a reply to message #34058 ] |
Mon, 12 March 2007 17:23   |
Lukas Heyer
Messages: 54
Registered: September 2005 |
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| 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.)
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Oliver, it would be very interesting to see the test circuit's schematics - can you or anyone else here please share it with the rest of us?
Many thanks,
Lukas
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| Re: Telefunken AC 701 Tube Primer [message #231027 is a reply to message #32580 ] |
Tue, 20 March 2007 08:04 |
 Frankenheimer
Messages: 26
Registered: March 2007
Location: Austria |
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Hello Klaus,
i found a tube from 1965 from the Ulmer Factory.
Details: U3206503, lfd. Nr.4333. (Bj. 1965).
Is it worth buying fo a C60 ?
The dealer told me that the tube is original, no thrown out neumann or AKG stock.
The cost is about 300¤.
Thanks in advance
Franz
Franz Skale
https://i.bin.dah.am
http://www.kolab.org
http://www.ardour.org
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| Re: Telefunken AC 701 Tube Primer [message #231096 is a reply to message #231027 ] |
Tue, 20 March 2007 12:42 |
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Klaus Heyne
Messages: 1955
Registered: April 2004 |
Platinum Member |
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Whether it's worth it depends on your love for the AKG C60 mic, and how much you have already invested.
You should read the beginning of this Stickie once more:
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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.
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Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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| Re: Telefunken AC 701 Tube Primer [message #250858 is a reply to message #250830 ] |
Sun, 10 June 2007 10:11 |
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Klaus Heyne
Messages: 1955
Registered: April 2004 |
Platinum Member |
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To my knowledge, there was no tube selection at the Neumann factory beyond the low-noise preselection which was performed regardless of final mic destination.
I.e., pair selection for tubes was probably not performed, as far as everything I have read and know.
So you should be fine once you have found a low-noise specimen AC701, even for a stereo mic application
Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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| Re: Telefunken AC 701 Tube Primer [message #291160 is a reply to message #32580 ] |
Wed, 21 November 2007 15:20 |
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Klaus Heyne
Messages: 1955
Registered: April 2004 |
Platinum Member |
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Not all genuine Telefunken tubes have the embossed diamond on the bottom. Besides, the AC 701 has four closely spaced filament wires sticking out of the bottom of the tube- there would be no space to add a diamond.
Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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| Re: Telefunken AC 701 Tube Primer [message #291161 is a reply to message #32580 ] |
Wed, 21 November 2007 15:20 |
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Klaus Heyne
Messages: 1955
Registered: April 2004 |
Platinum Member |
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Not all genuine Telefunken tubes have the embossed diamond on the bottom. Besides, the AC 701 has four closely spaced filament wires sticking out of the bottom of the tube- there would be no space to add a diamond.
Klaus Heyne
German Masterworks
www.GermanMasterworks.com
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