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Tube Physics Question

At least I think it's Physics. 

Short version:  Is it logical that going to a less powerful power tube in an amp can yield better dynamics?  What's the Physics behind tube design/operation and their ability to reproduce the swing of musical dynamics?  What part does bias play?

Longer version:  A couple of years ago I acquired a used tube amp for a second system.  It came with three sets of power tubes - the original KT88s, a set of Gold Lion KT88s and a set of Tung Sol KT120s.  The amp had been biased for the 120s, and those are what I used and have been happy with.  More power = better, right?

Recently I swapped out the speakers in that system for a more efficient and transparent pair.  While the change was nice and an obvious speaker upgrade, I started hearing a little edginess in the treble.  Since I'd never checked the bias I put a meter on it and found it low (avg ~12mV vs. a recommended 45-50mV for KT120s).  Running the pots up to max only reached ~35mV, but it did improve the sound.  Called the mfr and he said not to worry about a lower bias setting, as it made little difference.

Not content, I swapped out the KT120s for the Gold Lion KT88s, checked/reset bias to 35mV (recommended for 88s) and wow, what an improvement they made.  Without getting into a bunch of hyperbole, what was immediately and most noticeable was the increase in dynamics.  So my question is, what about the design/production and implementation of a tube affects its ability to reproduce dynamics?  Or is it more likely that running a lower power tube at relatively higher bias causes the effect?
tmcclintock
mechans
3,048 posts
 
I think it was Nelson Pass who said or made famous the phrase "If the first watt is not good  why would you want many more of them?" Or 100s more of them etc. 
The answer to your question can be ascertained by looking up the parameters available from the current manufacturer. Try your question on tube forums, like audio asylum tube asylum, for additional discussion.

The real answer however  is simple. Magic! 
wolf_garcia
6,626 posts
 
The Tiger was kind of fun (a friend had one) and seriously cool but didn't handle so well.  From that era I preferred a Lotus Elan I was lucky to drive for a bit as those were REALLY fun, and felt very fast. 

Nelson Pass is too cool. Somebody wrote about hanging out with him listening to a First Watt amp with a meter showing how many watts were being used while listening to some fairly loud music…around 3 or 4 watts or so max, with not particularly efficient speakers. The "first watt" idea is completely correct and can be illustrated by any electric guitar player…try a 50's era Fender Tweed amp (Julian Lage uses 2 of these live…a beat up looking Champ and a Deluxe) and see what a first watt can sound like.


tmcclintock OP
35 posts
 
Thanks, glassandlight.  The part about not being able to adjust bias to the point spec'd for the 120s seems legitimate in my case and part of my original question.  The 88s operate in their range, the 120s don't.

As to what's physically different about the tubes, I'm OK with the magic answer.

Re: Sunbeam Tigers, revving up and dumping the clutch would make the leaf springs buckle like crazy.  No wheelie bars needed.  (currently checking out a hi-po 289 swap for my M3)
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