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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 21 May 2019, 17:02

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PostPosted: 15 May 2019, 02:42 
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Joined: 24 Oct 2010, 07:05
Posts: 288
In my opinion the regulator is fine, you have the values of C27 and C30 too low. C27 should be 100 times or more bigger in value (10mF or more), C30 - 1mF or more. That is why you have too low input voltage for the regulator and too big differences between loaded and unloaded.
I also think that the current rating for heaters secondary is rather low. The rated power for the secondary is 8 x 1.5 = 12W. Tubes draw 1.2A x 6.3V (7.6W). LT1085 needs at least 1V dropout, so draws 1.2A x 1V = 1.2W more. Rectifier diodes draw 1.2A x 0.7V x 2 = 1.7W. The typical transformer of the range has around 8% regulation, so the 8% comes to the heat dissipation in the transformer. Total draw in your case is (7.6+1.2+1.7) x 1.08 = 11.3W. In reality the output was higher (to preserve a margin for mains fluctuations) and you easily exceed the ratings.


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PostPosted: 15 May 2019, 10:38 
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Joined: 04 Jun 2008, 20:59
Posts: 3960
Location: Arizona, USA
Hi, The math is right, but the transformer is more robust than it would seem. I use them in the 5 tube version and have done so for about 7 years now with no ill effects. The 5 tube versions are used in my main system and a number of beta versions floating around and never have had any problems. I did not look at the exact circuit values the poster used (my bad) but the values in the posted project work well. BTW the commercial preamps that are nearly ready for laund (finally) use the same transformers.

Good listening
Bruce

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