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Why do some people dislike ultralinear?

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#362
I have to say this thread has certainly been thought provoking. I have never had a problem with my 49 year old UL amp SQ wise and I reckon its about as good as you get for a 30W PP EL34 UL design with huge (for tubes amps) GNFB. So now my challenge is can I do similar, but with more power, but also exploring the trade offs between more power vs control of overload. Towit. On my current speakers 30W is not quite enough. You need that 6dB of headroom on classical that a 100W gives you. But as long as the 1-5W range is low (0.1%ish) THD does is actually matter if those short peaks are 2%? And this is where I am fascinated by the work done on this forum with TV tubes as, other than the EAR509 there has been very little commercial interest that I know of.

Mildly OT, but the more exploration of triode vs UL vs Pentode there is the better for all of us. Esp once you look at the more advanced circuits with some added sand to help things along. tis a good time to experiment with tubes 🙂
 
#363
Ufudu: thanks for the 60% UL curves. One can see the effective Mu change and the "knee" move down versus higher UL. Looks like the UL "knee" follows the diode curve down on the left of the pentode traces.

This uTracer is quite useful for evaluating UL curves. (needs the % screen current added in yet I guess) For the 1st time we have a good picture of what is going on with UL. One can make some intelligent choices for optimization.

It would be nice if the uTracer software allowed a specific measurement trace along a specified load line (and bias), with some analysis of gain versus input V.
One could play with load lines for any tube then, and find the optimum power or distortion pathes.
 
#364
Hylle said:
Gingertube I would like to know how low outputresistance/low dampingfactor is possible with the designs you describe without global feedback?
Click to expand...
I am typically getting a damping factor of around 2 without global feedback, not great but sufficient, close to typical SET amp values with the Ultralinear + balanced shunt feedback (Baby Huey) scheme. I hope to do better by adding cathode feedback in to the mix.
I have some Plitron VDV-2100-CFBH output trannies to play with. They have 30% UL taps and 10% cathode feedback windings. When using both, the UL feedback effectively becomes 30% + 10% = 40% (as stated by Johan above).
Cheers,
Ian
 
#365
obseedian said:
Of all the amps I have built so far, the best ones were push-pull DHT stages with well filtered B+ supplies, or PP pentode stages with G2 voltages far below B+. My sims showed that UL stages did offer lower overall distortion but only for lower order components, higher order components become much more prominent. Also, a PP pentode stage with regulated G2 is far less susceptible to B+ ripple inter-modulating with the signal because of its high plate resistance, again confirmed with simulation. Interestingly, this advantage is nullified when using plate-to-grid (Schade) feedback because the B+ ripple is now fed into the driver stage.

My 807-based pentode-connected Williamson sounded far better than I expected. Originally that amp was going to be UL but I switched it to pentode because B+ was too high to put on 807 screens. It was a total revelation and made me question all the various audio fads and orthodoxies about amp design.

Personally, I think the success of UL has nothing to do with sound quality and everything to do with economics.
Click to expand...

agreed, also my experience with TV scanning tubes, am also one who favors pentode mode with G2 supply fed from a low impedance voltage source, regulated is better...
 
#366
AJT said:
... am also one who favors pentode mode with G2 supply fed from a low impedance voltage source, regulated is better...
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what do you mean by low impedance, is it sufficient to have a big cap decoupling the screen supply to ground ?

what sonic penalty do you hear if the scree supply is not low impedance ? - I have a tetrode spud amp I'm playing with and it would be easy to do some experiments.
 
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