Which Power Tube ?

Discussion in 'Audio Hardware' started by iDigital, Apr 16, 2019.

  1. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    Hi All, I am just about to have a stereo set amp built, using available power transformer that was running a 6V6gt in set mode that I scavenged from a late 50’s to early 60’s console that I bought here in Australia, I could stick with the 6V6gt in set or, I could also use the original power transformer for either 6l6, el84 or el34, all in set mode, 6V6gt and el84 in set will produce 5 watts and the 6l6 and el34 will give 10 watts in set, I am tending to go with el34 for this project, but, I just don’t know, my room is small and I no longer play loud music, so power is not a issue here, is there a big difference from 5 watts to 10 watts with tubes mentioned ? I mainly now listen to bluegrass, folk country, the real old stuff, also include 1920’s to 1930’s blues and jazz, with some classic rock, some insights into these different power tubes to help me decide would be much appreciated. Thanks
     
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  2. Warren Jarrett

    Warren Jarrett Audio Note (UK) dealer in SoCal/LA-OC

    Location:
    Fullerton, CA
    I am using speakers that are about 97 dB efficiency, and I have compared using dual 2A3 amps ( running in parallel SET, producing 8 wpc), to dual 300B amps (also parallel SET, 18 wpc). Both were very similar in design and in their parts quality. I heard no improvement from the 300B's higher power, only the differences in sonic character between the different power tubes.

    In another comparison, using 88 dB efficiency speakers (and known to present a widely varying impedance curve to the amps, a "difficult" load), I compared 211 (45 wpc SET) to 6550 (120 wpc Push-Pull). In this case, I DID hear the greater power to its advantage, even though I was not playing loud enough that the power was necessary for overall loudness.
     
    Last edited: Apr 16, 2019
  3. Larry I

    Larry I Forum Resident

    Location:
    Washington, D.C.
    I like all three of the tube types you listed, although I like the 6L6 slightly more than the other two. In the right build, it can deliver a nice balance of dense, well-saturated (harmonically complete) sound and reasonable dynamics. I particularly like its cousin the 350 tube, but, that has become an ultra-expensive tube.

    The EL84 amps I've heard tend to be budget amps, but, most of the amps I heard with this tube sound very good--lively without being hard or bleached sounding.

    I've also heard a lot of EL34 amps that sound very good. But, I've heard some amps, particularly those pushing for extra power, sound just a bit too hard and brittle for my taste. Still, if you need a bit more juice, it is a nice tube to work with.

    I run 99 db/w speakers that I tend to play at lower volume levels. The tubes I currently run are pushpull 348's (similar to 6F6). The custom builder said it is good for around 5.5 watts per channel. This is plenty enough for me, even when playing something like Mahler's 8th symphony. I also own a parallel SET 2a3 amp (Audio Note Kageki) which is not much more powerful and it has enough output.
     
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  4. Subagent

    Subagent Forum Resident

    Location:
    Arlington, VA
    As I am running an amp that uses them, I am partial to 6L6's. I've never compared them to EL34 in the same amp, but do prefer them over the EL34 amps that I have run. One side benefit is being able to acquire a NOS quad (18 watts single-ended in my setup) for much less than NOS EL34's. But the primary reason is the sound.
     
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  5. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    I did come across some info last week that the 6v6 has 90% the linearity of a 45 tube and also, the EL34 is the only 8 pin tube that doesn’t have the suppressor grid internally connected to the cathode, which makes it possible to wire the tube as a true triode for SET
     
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  6. KT88

    KT88 Forum Resident

    Build it for the EL34 / KT88. You should be able to sub in a 6L6GC then if you like, but the higher power of the others is likely most beneficial. If you were talking about the advantage of a 100w amp vs a 200w amp, then I would agree that 100w is already overkill. But when you are limited by a 5w output, you are really limited. You'll get way more headroom and thus flexibility in speaker and room choices using the higher power tubes. With most speakers, 10w is pretty loud, 5w isn't always and it can also suffer from compression.
    -Bill
     
  7. allied333

    allied333 TUBE AMPLIFIER REBUILDER - inquire

    Location:
    MI
    I tested a lot of tetrode & pentode tubes. The best I ever heard and better than RCA 45 triode tube is a Sylvania JAN CHS 7C5 triode connected. It is a 6V6 in an octal socket. Other Sylvania 7C5 are not near as good and the JAN CHS 7C5 mentioned uses the same plate as expensive Sylvania 6V6G (coke bottle glass). Triode connected is about 3 watts for single tube (SET) or 6 watts for push-pull. If using a SET design, parallel two tubes for 6 watts output.

    There are five new JAN CHS 7C5 for sale in your country right now and advertised on USA ebay for $25.
     
  8. SandAndGlass

    SandAndGlass Twilight Forum Resident

    The EL34 is a true Pentode. I believe that tubes that have the suppressor grid internally connected to the cathode are beam tetrode designs.

    I have a Decware 3.9-Watt dual mono 6V6GT based Single Ended Pentode.

    The 6V6GT is not as powerful as the 6L6, but they are nicer sounding tubes.
     
  9. TarnishedEars

    TarnishedEars Forum Resident

    Location:
    Seattle, WA
    I would go with a 6L6GC design myself. The tube rolling options within that family of tubes is better than just about any other tube today.
     
  10. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    After some more deliberation, I am still feeling that the el34 in set mode is the way to go, but, I am becoming very curious also, about how the 6v6 in set mode would compare, any thoughts and/or suggestions on this ?
     
  11. Marshall_SLX

    Marshall_SLX Forum Resident

    KT88 (6550 almost as good) would be the ultimate for the flattest response IMO but out of the ones mentioned ide say the 6L6 suits your listening habbits better than EL34... only because it tends to be a bit warmer with more bloom and extension in the low end and sounds sweeter in the highs... mids are smoother and more relaxed than EL34... for classic rock with barky guitars EL34 does it better... less extension but a firmer tighter low end... forward mids with great depth and detail... somewhat analytical highs with pleanty of sizzle but thats tube dependant some have sweeter highs... i use 6CA7 tubes which are a drop in replacement for EL34 but present as a bit of a halfway point in sound between EL34 and 6L6... same low end sound with better extension... still forward mids but not as fatiguing... sweeter highs though still not quite as nice as 6l6, 6550 or KT88... theres also the KT77 which is in the EL34 family though its not quite a drop in replacement... i havnt much experience here but i believe its darker with a much fuller low end... similar highs and more muscular mids... though some find it muddy
     
  12. TarnishedEars

    TarnishedEars Forum Resident

    Location:
    Seattle, WA
    EL34s can sound wonderful in the mids. But in my experience they are more load sensitive than are 6L6s. It just seems like EL34s are more speaker dependent than are other output tubes. But I've never heard a 6L6 run in triode mode. So for all I know they could easily stink in that application.
     
  13. allied333

    allied333 TUBE AMPLIFIER REBUILDER - inquire

    Location:
    MI
    For what my experience is worth, perhaps nothing but the 7C5 I mentioned will blow the EL34 away.
     
  14. SandAndGlass

    SandAndGlass Twilight Forum Resident

    You don't mention the sensitivity of your Hitachi Floorstander's?

    If these speakers are of conventional direct radiator's design, then they might fall in somewhere around 88-90 dB.

    I really don't see how you are going to have any power, control or dynamic impact with either 5 or 10 watts using speakers of this design.

    I have several tower speakers that I use or have used and I never power them with tube amplifiers (Except for the sensitive Zu, Omen Definition's), only SS power and plenty of it.

    I can run the Vintage Altec Lansing A7's off of 3.9-Watts because they are high sensitivity horn speaker's, with a sensitivity of around 103-dB.

    [​IMG]

    Even then, I still use at least a 300-Watt 12" home powered sub. With 3.9-Watts I can get nice room filling volume, but I wouldn't be blowing any doors off.

    I think you will need more power than a small 5-10 Watt SET.

    I think you will be better served running the power tube of your choice in class A/B.
     
  15. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    Hi, I plan to change my speakers to suit the amp, plus, I don’t play loud no more
     
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  16. SandAndGlass

    SandAndGlass Twilight Forum Resident

    It is not a question of playing loud. Without really efficient speakers, you are not going to get anywhere loud with a 5-Watt amp. A 10-Watt amp will give you an extra 3 dB.

    You either need power or high sensitivity speakers when you get in the 5-10 Watt SET type amps.

    You want to produce a big, full sound with impressive dynamics.

    Even then, I need a moderate size subwoofer to provide the needed bass.

    My horn loaded cabinets are highly sensitive, but the Altec 828 bass bin's only play down to about 48-Hz. at their -3dB. point (which is fine), plus, it simply takes more power to reproduce sound at lower frequencies, that you can hear.
     
  17. Rolltide

    Rolltide Forum Resident

    Location:
    Vallejo, CA
    Something to keep in mind is I don't believe anybody makes a true EL34 Pentode tube anymore, and NOS "real" EL34 tubes are very expensive now. I personally am not a fan of any current production EL34/6CA7/KT77 tube. I think you should definitely factor in the actual tubes you'll use and where you'd source them from when making your decision.
     
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  18. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    I did wonder about that
     
  19. iDigital

    iDigital Well-Known Member Thread Starter

    Location:
    Australia
    So, to reiterate, if no one makes a true el34 pentode, then, what are they making ?
     
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  20. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Good question?
     
  21. Marshall_SLX

    Marshall_SLX Forum Resident

    So is an EL34 you get from JJ right now not faithful to the NOS stuff?
     
  22. IanL

    IanL Forum Resident

    Location:
    Oneonta, NY USA
    6L6GC. I love GEs overall, and for their dimensionality, but RCA black plates are also very nice and dig deeper in the bass if you need it.
     
  23. Rolltide

    Rolltide Forum Resident

    Location:
    Vallejo, CA
    Beam Tetrodes. Something to note here is that a Beam Tetrode is "better" then a Pentode. What the square quotes imply is that while today we're nostalgic for the tones of tube amps and their second order harmonics, the goal in those days was to make a better mousetrap, defined as more linear with less distortion. In other words, the goal was to make tubes less tubey and more transistory. To me, a lot of these current issue tubes in modern amps end up sounding like solid state amps. Which is fine, but defeats the purpose and joys of using baroque technology that could explode at any minute.
     
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  24. SandAndGlass

    SandAndGlass Twilight Forum Resident

    When the Pentode had been invented in England (I believe), the design was patented.

    In America, they came up with an alternate take on the pentode, which was a sort of a pentode, but not technically speaking.

    The design was known as a Beam Tetrode, which turned out to be an actual improvement on the pentode design.

    "The problem of secondary emission from the anode (US: plate) in the tetrode tube was solved by Philips/Mullard with the introduction of a suppressor grid which resulted in the pentode design. Since Philips held a patent on this design, other manufacturers were keen to produce pentode type tubes without infringing the patent. In the UK, two EMI engineers, Cabot Bull and Sidney Rodda, produced and patented an alternate design in 1932.[2] Their design had the following features (compared to the normal pentode).

    • The control and screen grids were wound so that the pitches were the same and the wires were in alignment (the pentode used different pitches).
    • A pair of beam-forming plates was added at the two ends of the oval grid structure to focus the electron stream into a pair of beams 180 degrees apart (the pentode added a third grid). These plates are normally connected to the cathode.
    The design is today known as the beam tetrode but historically was also known as a kinkless tetrode, since it is a four-electrode device without the negative resistance kink in the anode current vs anode voltage characteristic curves of a true tetrode. Some authorities, notably outside the United Kingdom, argue that the beam plates constitute a fifth electrode.[3][4]

    The EMI design had the following advantages over the pentode:
    • The screen grid current was about 5-10% of the anode current compared with about 20% for the pentode, thus the beam tetrode was more power-efficient.
    • The design introduced significantly less third-harmonic distortion into the signal than did the pentode.[5]
    • The design produced more output power than a similar pentode.
    Disadvantages of the beam tetrode were:
    • It had higher inherent intermodulation distortion than the pentode. It could be reduced by adopting an ultra-linear design in a push-pullcircuit. This connection links the screen grids to taps on the output transformer. Negative feedback also reduced harmonic and intermodulation distortion.
    • The beam tetrode had smaller transconductance than a similar pentode and therefore required a larger input signal at the control grid for a given output power.
    • The beam tetrode had more tendency to oscillate than a pentode if the circuit was not designed and laid out properly.
    The MOV (Marconi-Osram Valve) company, under the joint ownership of EMI and GEC, considered the design too difficult to manufacture due to the need for good alignment of the grid wires. As MOV had a design-share agreement with RCA of America, the design was passed to that company. RCA had the resources to produce a workable design resulting in the 6L6. Not long after, the beam tetrode appeared in a variety of offerings, including the 6V6 in December 1936, the MOV KT66 in 1937 and the KT88 in 1956, designed specifically for audio and highly prized by collectors today.

    Some tubes described as pentodes are actually beam tetrodes. The ubiquitous Mullard EL34 (6CA7), although manufactured by Mullard as a pentode, was also produced by other manufacturers as a beam tetrode instead.
     
    Last edited: Apr 19, 2019
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  25. allied333

    allied333 TUBE AMPLIFIER REBUILDER - inquire

    Location:
    MI
    The USA tetrode was patented. So, Europe came up with the pentode to avoid tetrode patent infringement.
     

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