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Re: Read the Tube Amp FAQ

2/7/2000 6:19 PM
Re: Read the Tube Amp FAQ
If a transformer was wound with the intention of presenting an 8k load when connected to an 8ohm speaker, it will also have a certain inductance and low frequency rolloff associated with it's design requirements. An 8k transformer requires substantially more core inductance than one wound for a 4k load requirement, in order to achieve the desired low frequency power response.  
If you deliberately load an 8k transformer to only 4k, the likelihood of core saturation inductance limiting is less, compared to the reverse, or trying to utilize a 4k-wound transformer for a circuit that desires an 8k load. The 4k transformer had enough inductance to maintain a certain low frequency power limit, it may likely have not enough when asked to maintain the same low frequency power response with an 8ohm load on the 4ohm tap to double its reflected impedance.  
Changing a transformer characteristic like primary inductance will have an effect on the amp's overall frequency response. At higher tube current swings, inductive loads produce elliptical load lines on the characteristic curves. Power output and harmonic distortion vary as the load line varies. Much of the reflected load characteristics is contingent on how the actual speaker's complex impedance behaves at each frequency & power level.  
So, matching a tube's required load by alternate reflected load connections (like using an 8k/8 transformer for use as a "4k" transformer) is ok to do. It won't hurt anything. But it will sound different, just like all transformers that are bigger/smaller, or have different layering/interleaving type construction, act differently and sound differently in the same tube output circuit.
2/8/2000 12:18 PM

Thanks, Doc,  
I suppose that's good to hear -- means there are still more variables to play with regarding original components (ie there IS a difference in a 4k ohm OT), which makes it all the more worthwhile tinkering around to find that individual tone recipe.  
By the way, any ideas about how I can alter the interactive Matchless Lightning tone stack/preamp (basically Vox TBX, I suppose) to make it more "Fender guitar friendly" and not so harsh with my Tele? A bit beefier from the preamp and not so shrill in the high end?  
All the best,  

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