Carlo
 | Re: 3800 ohms!
Here's some info that i found:
Mike B mmbb@frontiernet.net 8/12/99 Re: Another spitfire question: OT
quote:
"The measured primary impedance on a Spitfire OT was around 4K (I think Doc measured 3.8K)... Why does it sound better? For a given tube type, there is an optimum impedance that provides a reasonably high level of output power with a reasonably low level of harmonic distortion. The 8K value is what the tube manufacturers specified as the compromise to achieve a good power to distortion ratio for the El84/6BQ5 (for hi-fi, not guitar!). By lowering the primary Z, distortion and power are both increased. It appears that Mark Sampson, the designer of Matchless amps, did a lot of experimenting with this to find the optimum value for guitar. I have played around with this quite a bit myself, and I agree with your findings - lower primary Z results in a 'beefier' tone, for lack of a better word. Switching back to 8K thins the tone out. There is probably a better technical explanation for exactly what's going on here, so hopefully someone can shed some more light on this. From a purely practical point of view I design all my EL84-based amps with a 4K primary Z, since the tonal difference is significant, at least to my ears. Hope this helps..." |
SpeedRacer 8/12/99 Re: Another spitfire question: OT
quote:
"To elaborate more on Mike's excellent post, the distortion and power do vary with load imp, and more to the point (of tone) the MIX of harmonics changes.. typically you have a greater % of 2nd at lower loads, which drops as you increase the load and while that occurs, the odd order HD tends to increase. Your max power point is (generally) a point where the 2nd HD is trailing and the 3rd (and higher) hasn't really climbed yet. There's a great chart in one of the RCA books with the 6L6's reponse at given loads. Your harmonic mix can have a profound effect on the tone of the transformer and how it reacts to the rest of your amp circuit. I say "can" rather than "does" BC I've found in my own research that load changes of as little as 10% can be very audible when incorporated into the wind of a tranny, but I've also mis-loaded the 2ndary (say on a Fender) by a factor of 100% and not noticed as big a change.. It's very peculiar. Reliability-wise, low loads will tend to increase plate current and can lead to reliability issues (as noted)." |
Thanks for the info guys!
Carlo
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1/25/2000 10:12 PM