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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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    Triode vs. Pentode

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    VikeMan


    Posts : 3
    Join date : 2010-11-21

    Triode vs. Pentode Empty Triode vs. Pentode

    Post by VikeMan Tue Nov 23, 2010 11:09 pm

    So my ST70/VTA70 arrived today and I put it through its paces. So far I'm pretty happy! I did notice something I wasn't expecting though... I listened to one song (Porcupine Tree's 'Shesmovedon') several times, in pentode and triode mode. I was expecting the bass to more or less disappear in Triode. But it didn't...in fact I'm more than half convinced that the bass was more prominent in Triode. Now, I'm talking about bass guitar here, which goes down to roughly 40 hz, and not pipe organ, but still... more comparisons are in order I think.

    Anyone experience anything similar?

    ---VikeMan
    Bob Latino
    Bob Latino
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    Posts : 3258
    Join date : 2008-11-26
    Location : Massachusetts

    Triode vs. Pentode Empty Re: Triode vs. Pentode

    Post by Bob Latino Wed Nov 24, 2010 6:11 am

    VikeMan,

    In pentode/ultralinear mode, your VTA ST-70 amp is flat to about 17 HZ. In triode mode it is flat to maybe 20 - 25 Hz. Most speakers don't go down to that range anyhow. As such, the bass rolloff is virtually unnoticeable when you switch to triode mode. You don't have less bass in triode but you do have less bass POWER and less bass headroom in triode.

    In triode it appears (to me at least) that the mid-range comes "forward" in the soundstage just a little. Some people like the effect and maybe some don't. Triode is really nice for vocals and acoustic jazz. If you are a rock fan then you would probably prefer pentode/ultralinear mode which has more power and bass "slam".

    Bob
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    ejc


    Posts : 33
    Join date : 2010-10-16
    Age : 73
    Location : Connecticut

    Triode vs. Pentode Empty Re: Triode vs. Pentode

    Post by ejc Wed Nov 24, 2010 3:07 pm

    Bob Latino wrote:VikeMan,

    In pentode/ultralinear mode, your VTA ST-70 amp is flat to about 17 HZ. In triode mode it is flat to maybe 20 - 25 Hz. Most speakers don't go down to that range anyhow. As such, the bass rolloff is virtually unnoticeable when you switch to triode mode. You don't have less bass in triode but you do have less bass POWER and less bass headroom in triode.

    In triode it appears (to me at least) that the mid-range comes "forward" in the soundstage just a little. Some people like the effect and maybe some don't. Triode is really nice for vocals and acoustic jazz. If you are a rock fan then you would probably prefer pentode/ultralinear mode which has more power and bass "slam".

    Bob

    Can you switch fro triode to pentode on the fly or do you have to shut down and restart
    Bob Latino
    Bob Latino
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    Triode vs. Pentode Empty Re: Triode vs. Pentode

    Post by Bob Latino Wed Nov 24, 2010 4:02 pm

    Can you switch from triode to pentode on the fly or do you have to shut down and restart ?

    On the VTA ST-70 or ST-120 kits you can switch from triode to pentode or pentode to triode on the fly. It is not necessary to shut the amp off to make the switch.

    Bob
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    Disles1


    Posts : 17
    Join date : 2010-12-21
    Location : Calgary, Alberta

    Triode vs. Pentode Empty Re: Triode vs. Pentode

    Post by Disles1 Sat Mar 19, 2011 10:11 am

    Bob Latino wrote:

    In triode it appears (to me at least) that the mid-range comes "forward" in the soundstage just a little. Some people like the effect and maybe some don't. Triode is really nice for vocals and acoustic jazz. If you are a rock fan then you would probably prefer pentode/ultralinear mode which has more power and bass "slam".

    Bob

    Bob, I listened to an LP yesterday of Mike McDonald former singer with Doobie Brothers, in both triode and pentode mode. Mike has a nice somewhat-soft bluesy voice; the selection had a good strong drum beat. I think the type of music on this album helped me distinguish the difference between triode and pentode in my system so I thought I would add another interpretation to your note that the "mid-range comes forward." In some peoples' minds that comment may mean something different than what you intended. When I listened to the music on this LP, I found that in triode mode the drum beat was a little less strong than in pentode mode - as if the drummer reduced the power of his whacks - allowing Mike's voice to be the prime focus. This may be what you mean by "coming forward" however in my mind the voice doesn't come forward, it just becomes more the focus than the drum beat. Ken
    Bob Latino
    Bob Latino
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    Triode vs. Pentode Empty Re: Triode vs. Pentode

    Post by Bob Latino Sat Mar 19, 2011 10:40 am

    Hi Ken,

    You have a point there ... In triode mode the extreme top and bottom end is rolled off very slightly. When you combine this with the lowered output of triode (triode mode only has about 60% the power of ultralinear mode) you have less bottom end extension AND less dynamic headroom in the bass. On some speakers with limited low frequency extension this lowered triode mode bass extension is barely noticeable. On other larger speakers with greater bass extension, the effect would be more noticeable.

    Bob

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    Triode vs. Pentode Empty Re: Triode vs. Pentode

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