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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Very important! posted by Allen Wright on May 20, 2009 at 05:21:52:
Hey! Let me be the biggest poop disturber. If you have a long tailed phase inverter, one output is taken from the Plate, whilst the other is taken from the Cathode. These will have different impedances, so the frequency response cannot be the same. The phase inverter won't be perfectly balanced, and the output transformer won't be perfectly balanced, so what are you worried about? Get it close, but don't lose sleep about getting it to within .00025% or better.
Here is another fun experiment you can do to really mess with your thinking. Set your bias. Get the two output tubes idling EXACTLY the same. Go through 912 tubes to find two this closely matched, but this is worth it. Now where is your bias voltage at? If you have a CAV50, it may well be about -38VDC. Now set the bias to -35VDC and then -45VDC. Did the static Plate currents track each other in a linear fashion? Of course not. Your input signal will vary the bias just as you did.
My attitude has always been 'get it close without taking forever, and then stop worrying'. The tubes will also age differently, so if by a one-in-a-million chance you found two tubes that tracked each other perfectly, in ninety days they won't. Be realistic and get it as good as you can in a timely manner, and if you don't have differential stages in YOUR amplifier, that's all you can do.
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Follow Ups
- RE: Very important! - Mr. Droopy-Drawers 18:34:49 05/20/09 (5)
- Um, wrong terminology..... - JimL 20:31:26 05/20/09 (0)
- long-tailed PAIR - TimFox 19:29:14 05/20/09 (3)
- RE: long-tailed PAIR - Mr. Droopy-Drawers 17:45:58 05/21/09 (2)
- RE: long-tailed PAIR - PakProtector 17:28:25 05/26/09 (1)
- RE: long-tailed PAIR - Mr. Droopy-Drawers 19:08:04 05/27/09 (0)
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