Why do some people dislike ultralinear?

[ray_moth]

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)?

[aletheian]

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.

[Eli Duttman]

Ray,

To squeeze the absolute maximum out of ultralinear topology, a separate screen grid winding connected to a dedicated/regulated supply is needed. The rationale is the same as for pure pentode mode. Such "iron" is costly.

[Salas]

As typically as it is implemented in amplifiers that have a triode/UL switch, the triode mode is sounding bigger, with less harshness, more depth & sonic info. Some say that UL screws the 1st Watt linearity although its total bench result seems best preferable.

[aletheian]

Originally posted by Eli Duttman
Ray,

To squeeze the absolute maximum out of ultralinear topology, a separate screen grid winding connected to a dedicated/regulated supply is needed. The rationale is the same as for pure pentode mode. Such "iron" is costly.

Is the requirement lessened any with KT88 and it's variants with a regulated plate supply and strice class A? I would think so.

[Eli Duttman]

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.

[aletheian]

Originally posted by Eli Duttman



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. [/URL]

Ah, i see... i was assuming that with regulation and avoiding the fluctuating current demand of class AB, the issue of screen regulation would be less important.

[Kent Smith]

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.

[tubelab.com]

As typically as it is implemented in amplifiers that have a triode/UL switch, the triode mode is sounding bigger, with less harshness, more depth & sonic info. Some say that UL screws the 1st Watt linearity although its total bench result seems best preferable.

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.

[ray_moth]

I wonder if the particular speakers used could have anything to do with it? Or maybe an inferior OP transformer would give unpleasing results?