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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: RE: A tube journey with lesson learned, Re; KT88 & KT150 posted by hahax@verizon.net on February 1, 2024 at 20:44:22:
Usual thing isn't it.
If you check you will find ALL valve amps measure FR and distortion at 1W into a resistive load (although you won't see it admitted).
I always measure mine at -2dB from maximum load with both sine and square wave into a genuine inductive/capacitive load (a speaker array) at all frequencies from 40hz-25khz..
(it's LOUD!).
One thing that immediately came across was the very astonishing difference in measured waveforms across the load depending on the amount of negative feedback.
That tells you that the obsession with damping factor is manifest rubbish.
It also tells you current drive (which has v high damping factor) can well resolve speaker driver reactions at medium to high frequencies - but of course NOT such stuff as ESL capacitive loads.
Driving into resistive loads (dummy 50W resistor mounted on a large heatsink), tells you sweet zilch,especially at 1W which is why this entire industry is full of fakery and BS.
A 5W amp running at 1W with a small transformer and cathode bias+loop NFB is a very different animal from a 100W amp running a large transformer at 1W..and mainly running CFB.
..never mind the very large differences in magnetic flux and reactivity on some of the older classics like UTC LS or Partridge compared with modern stuff with the much harsher sounding winding and core technologies.
It's why Partridge based British stuff, Citation, Scott or Fisher or certain Bogen have "that sound" which you can't do today.
FYI I use Scott OPT in my modern PPP amp, and they are fantastic.
Trancendar cloned them but they are gone now.
Both measurements and listeners agreed on them.
Clean v low IMD and v low THD.
Measure good - sound good.
ie.
Very far from the muffled distorting rubbish that's knocked out by people like Jadis for megabucks...
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Follow Ups
- RE: A tube journey with lesson learned, Re; KT88 & KT150 - ivan_terrible 22:20:58 02/01/24 (0)
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