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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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It is currently 19 Oct 2019, 06:10

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PostPosted: 26 Mar 2019, 11:37 
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Joined: 12 Jan 2018, 21:17
Posts: 10
Location: Dublin. Ireland
Thanks Bruce
Thats what I will do.

Steven


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PostPosted: 18 Oct 2019, 06:43 
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Joined: 31 Jan 2015, 17:59
Posts: 10
What is the best value for cathode resistors with ecc81? I have a lot of them.
Thanks


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PostPosted: 18 Oct 2019, 15:26 
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Joined: 04 Jun 2008, 20:59
Posts: 4032
Location: Arizona, USA
Hi, At the given voltages (180-225 B+) IMO there is no best value. There are several issues with ECC81s in this circuit. First the gain is way too much (instead of 7 it is 25). Too much for a line stage. Second the output impedance will be high....about 6.5K. It would be OK for a tube amp input of say 50K or more but might be unsuitable for a lot of solid state gear. All that said if you wish the best values I can determine are for both cathode resistors to be 100 ohms. This gives an idle current of 5.2 ma at 220volts. Output voltage into 50K is about +47/-31. Since you really need only about 1-3 volts it ought to be OK. The non-symmetrical range is likely to cause some harmonic distortion, but I have no way to tell short of building it. My guess would be that 1-3 volts output it should be in the sub 1% range. You can not bypass the lower cathode as the symmetry really gets bad there. I didn't check for higher B+ but it would seem to put the tube in a better range. Let me know what you have available and I re check it.

Good listening
Bruce

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