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Triode, UL or Pentode connection? What do you prefer?

Which mode?

  • Triode

    Votes: 36 44.4%

  • Tetrode/Pentode

    Votes: 19 23.5%

  • UL

    Votes: 12 14.8%

  • CFB

    Votes: 10 12.3%

  • Plate-to-Grid FB

    Votes: 9 11.1%

  • G2/Twin Drive

    Votes: 3 3.7%

  • Inverted Triode FB

    Votes: 1 1.2%

  • None of the above

    Votes: 3 3.7%
  • Total voters
    81
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kodabmx

kodabmx

Member
Joined 2011
#1
Taking inspiration from the AC or DC thread I'm posting this poll to promote hopefully a similar level of discussion.

Which do you prefer and why? Do you switch? The poll is multiple choice.
 
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#2
Pentode with feedback to the 1'St grid. Pentode has too hbigh output resistance to drive speakers, UL is ultra-nonlinear because feedback and control go through paths with different transfer curves, triode connection is like pentode with feedback to control grid with non-linear ratio. So, the best is, pentode with local feedback to the control grid. We already discussed it here many times during many years, and even back in 1938 Otto Schade advertised this approach in his famous article that people keep forgetting being hypnotized by fashion of triode connection and the word "Ultra" in UL name. 😀
 
#4
Pentode/tetrode, or real triode. I almost always use a bit of global negative feedback, so tetrode or pentode works fantastic for me. If I want a triode amplifier I'll generally go for a real triode, and I'm partial to the 6AS7G for that, however, triode connected 6V6 amplifiers give me a stiffy 🙂

For whatever reason I never really cared for UL. I always prefer pentode/tetrode to it when I've used it in the past.
 
#6
Lingwendil said:
Pentode/tetrode, or real triode. I almost always use a bit of global negative feedback, so tetrode or pentode works fantastic for me. If I want a triode amplifier I'll generally go for a real triode, and I'm partial to the 6AS7G for that, however, triode connected 6V6 amplifiers give me a stiffy 🙂

For whatever reason I never really cared for UL. I always prefer pentode/tetrode to it when I've used it in the past.
Click to expand...


My only UL amp is a KT88 100W using 60W OPTs. I like the sound better than tetrode connection but I wasn't using a regulated screen supply on that amp.


Generally I prefer triode connection, but where a cheap and cheerful 10W amp is needed, a 6P1P in tetrode works great.
 
#7
Any thoughts on CFB? Discusions on CFB should be as valid in this context as UL Have not tried or heard it but find the concept facinating. From what I read it need pentode or slight UL.feedback due to mu requirement.
 
#9
As is with global NFB, I believe it's all about the implementation. UL, pentode and triode modes can all sound good, when implemented well. And therein lies also the reason I don't believe in switching between modes, since no amplifier can be perfectly optimised for two or three modes at the same time. If you want UL, design for UL. If you want triode, design for triode. And so on...
 
#12
Adolf Corkscrew said:
As is with global NFB, I believe it's all about the implementation. UL, pentode and triode modes can all sound good, when implemented well. And therein lies also the reason I don't believe in switching between modes, since no amplifier can be perfectly optimised for two or three modes at the same time. If you want UL, design for UL. If you want triode, design for triode. And so on...
Click to expand...

Well put, and sort of how I like to do things. I like versatile designs, but each mode of operation has its own sweet spots, so to speak. I'm not a fan of switchable triode/pentode mode, or adjustable feedback. I prefer to set it all up a way that works/sounds best, and leave it.

Also, multiple modes is an excuse to guild multiple amplifiers, which is reason enough to do things this way 🙂
 
#14
Having tried them all at various stages, to me the most musical is class A triode. KT88's triode connected can supply about 18 watts. The amplifier to which I refer had triode stages, viz a triode connected EF86, a 6CG7 cathode coupled phase splitter, the KT88's. 20DB of feedback from the first cathode to the secondary of the output transformer.
 
#15
I used to do a triode, tetrode, UL switch on a PPP 6P3S amp, but eventually I realized I left it in triode all the time. The switch switched relays to short the extra biasing resistors, too. 6L6 in cathode biased tetrode is 9k Ra-a, triode is 8k Ra-a, so it worked well. Now I have a Yorkville AP1200 for when I need more power.
 
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