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77.43.10.3
In Reply to: RE: Novel Circlotron with 6 dB feedback posted by tesla on October 27, 2009 at 12:54:52
Dear Inmate,
I am quite convinced that SPICE does not lie.
In my personal experience if a circuit does not exhibit sound performance in simulations it will not work good in practice as well.
The schematic is quite new and, as right now it exhibits in my opinion too much distortion, I do not recommend to build it (unless you only desire to experiment with it or a practical way to overcome the known limitations is found). At the moment it should be considered as food for brain only. I have carried out some more investigations about the nature of the simulated distortion: it is mainly zero-crossing distortion (and this is bad new).
With the same components, at this time, there are better alternatives for OTL construction.
Best Regards
Luca Cellai
ecc230
because its models are lacking. As tubetvr mentions, there are no good models for 6C33s and there aren't any for 6AS7Gs either (although they like to make you think everything is fine). You'd think after nearly 20 years that they would have this sort of thing licked, but Microsoft has never been able to make Windows work in that some period either. As long as the software works 'good enough' to satisfy 95% of the industry, then the software company is likely satisfied not to go any further. It leaves people like yourself who want to do some serious 'fringe' modelling out in the cold.
You might try building one of these circuits and see what it **actually** does. It might be an eye-opener...
You are certainly right when you say that the only way to ascertain the goodness of a model is to build and listen (try some adjustments and re-listen). However my limited experience shows that the computer models I have used so far are quite accurate. When I say 'quite accurate' I mean that they are good enough for designing a good hi-fi tube amplifier (as I do not know the road to hi-end/excellence).
As a matter of fact I can not explain why I prefer listening to my OTL amplifier rather than the other one (with the output transformer) that I have built with the same tubes (12AT7, 6SN7 and 4x-6080/12AS7 per channel).
The transformer one is more powerful, it exhibits better measured performance but, whatever adjustment I have tried so far, I still prefer the OTL.
In conclusion, I think that the computer models are quite accurate in modeling electrical signal distortion, hum & bias, but they fail to model the real listening experience, which is a subjective very complex phenomenon.
Best Regards
Luca
ecc230
What spice model do you use for 6C33C? All models I have found on internet are useless and give very unrealistic results. The problem is that 6C33C doesn't behave like a normal trode at low currents and very negative bias, the (the curves are very bent). With available models distortion in simulations are too low by up to 10dB.
Sorry, I can not help, I have never tried any 6C33C model.
Best Regards
Luca
ecc230
Sorry, my mistake, I thought you where using 6C33C, (didn't you used that before?). Anyway, the problem with inaccurate spicemodels is valid for other power triodes like 6AS7, simulated distortion results are usually far away from reality and also sensitive to operating point. What model are you using for 6AS7?
See
http://www.duncanamps.com/technical/ltspice.html
The model of 6AS7 tube (tride model) can be freely downloaded in the LTSpice page at duncanamps.
Best Regards
Luca
ecc230
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