I have sometimes read that people who have tried ultralinear PP "didn't like it" and preferred triode PP operation, despite the loss of 50% of the power. I've even read cases where pentode mode sounded better than UL. However, I've never read any explanation for these findings.
If we are to believe the copious material has been published in support of UL since it became popular, it should be the "best of both worlds", in terms of distortion, power, output load flexibility and damping. Does anyone know any reasons for avoiding UL (assuming the OPT used is good enough for the job)?
If we are to believe the copious material has been published in support of UL since it became popular, it should be the "best of both worlds", in terms of distortion, power, output load flexibility and damping. Does anyone know any reasons for avoiding UL (assuming the OPT used is good enough for the job)?
i can't say that i personally 'don't like it', but I have never gotten the results the the published data sheet circuits suggest. Maybe the topology is more sensitive to other circuit variables than other topologies.... dunno, I am just a tinkerer. i have done my best to read all the associated literature and ancient articles, but despite all the published info and internet info from other builders, a catfight seems to erupt whenever the subject is brought up.
Is the requirement lessened any with KT88 and it's variants with a regulated plate supply and strice class A? I would think so.
I don't see where regulated plate B+ and Class "A" matter. When the instantaneous plate voltage drops below the screen voltage, linearity is poor. UL topology is just another form of local NFB. All NFB works best when things are reasonably linear to begin with.
Since KT88 variants were mentioned, look at the TT21. You can really max. out the plate/g2 differential with that tube. Somebody with "deep pockets" could come up with a VERY nice amp using TT21s and separate screen grid winding "iron".
TT21 data sheet here.
Since KT88 variants were mentioned, look at the TT21. You can really max. out the plate/g2 differential with that tube. Somebody with "deep pockets" could come up with a VERY nice amp using TT21s and separate screen grid winding "iron".
TT21 data sheet here.
I like UL, but it's not a perfect cure-all fix. Using the standard transformer taps, I usually have to tweak it with some series resistance to get it right.... or add global negative feedback. Pentode mode with good screen supply and some nfb can sound really good too. I dunno.... guess it depends on tube, topology, and preferences as to which path to follow. You can make a good or a bad sounding amp with any method.
There may be some truth in this statement, but I think that there is more going on here. I have built an SE amplifier that has a triode - UL - pentode mode switch. It also has switchable cathode feedback in the output stage. This amp has made the rounds of several listening sessions, and amp "sound off" tests. In a few cases the same people were present, but the room, speakers, and some of the music was different. In all but one case the preferences were not the same for each listener.
I use this amp in two situations. My living room is 12 by 14 feet. My speakers are made by puting modern Silver Iris drivers into a pair of 60 year old Zenith console radios. Sensitivity is 96 db. These speakers are loud with about 5 watts, so I usually use triode mode without cathode feedback. When I want to get really loud, I use UL with CFB.
My lab has Yamaha NS-10M studio monitors the efficiency is 86db. You need maximum power to drive these,so I use UL with CFB.
We took the amp to a friends house who had some 106db speakers. UL sounded terrible on these speakers. The amp played nicely all afternoon long in triode with no feedback.
There are experiments being caried out in another thread to determine if ul could be improved upon.
See the distributed load thread.
With sound systems in general, the good matching of drive-load-room-program, the well thought out system architectural priorities and the successful catering for them, can create synergy that can baffle our almost practically proven technical cornerstones.
But it should not baffle us at all, since these are two plains of thought that belong to a different level.
But it should not baffle us at all, since these are two plains of thought that belong to a different level.
The pentode or to a lesser degree UL sonic mark, owes a lot to global feedback (& local screen FB for UL). There is a cap in the pf range most of times on top of the FB return resistor. Many times its ceramic. Although on a scope screen it is adjusted to eliminate ringing to the trail of a 10kHz square wave and looks technically solid, I have experienced it producing moderate midhigh pinch and blackening of the soundstage. I would suggest experimentation with the quality of that cap.
I don't understand where this business of "U/L screws up the first Watt" comes from, particularly when coupled with comments about the linearity of a pentode when the anode voltage falls below the screen grid voltage. The anode voltage only falls below the screen grid voltage on negative peaks at maximum power - not minimum power...
I am with you on this one. Most recently a friend built an open loop U-L amp. 807's with a 10k a-a load. Three taps to choose from at 20, 30 and 40%. He has fairly efficient speakers( that are comfortable with SE2A3's ), and the First Watt is often in play. Can't say I heard anything I didn't like.
I build U-L amps as well, though they're E-Linear 2-stage types that have a fair bit of FB due to the E-Linear driver/PI connection. I don't think I've found the First Watt to be troubled with these amps. The speaker sensitivity is ~100dB 1W-1m and I am often in the sub-Watt power output range.
I don't remember reading *ANYTHING* about how U-L could screw up the first Watt until fairly recently. I think it is just a bunch ov propaganda or dogma...
I think I'll use my Truck-ma to deal with *THAT* dogma...
cheers,
Douglas
I build U-L amps as well, though they're E-Linear 2-stage types that have a fair bit of FB due to the E-Linear driver/PI connection. I don't think I've found the First Watt to be troubled with these amps. The speaker sensitivity is ~100dB 1W-1m and I am often in the sub-Watt power output range.
I don't remember reading *ANYTHING* about how U-L could screw up the first Watt until fairly recently. I think it is just a bunch ov propaganda or dogma...
I think I'll use my Truck-ma to deal with *THAT* dogma...
cheers,
Douglas
Reality check- at least a million UL amps have been sold or built. They've been around for 50 years. If there were truly a fundamental flaw, you'd think it would have been noticed by now.
It really gets down to the output transformer. UL is more critical than other topologies to how tightly the primary is coupled. Use a mediocre OPT and ultralinear will sound absolutely terrible. And then you can go on the internet and tell everyone that the topology is the cause.
It really gets down to the output transformer. UL is more critical than other topologies to how tightly the primary is coupled. Use a mediocre OPT and ultralinear will sound absolutely terrible. And then you can go on the internet and tell everyone that the topology is the cause.
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