The Dynaco Tube Audio Forum

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


    Triode vs. Pentode

    Share

    VikeMan

    Posts : 3
    Join date : 2010-11-21

    Triode vs. Pentode

    Post by VikeMan on Tue Nov 23, 2010 10:09 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
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Triode vs. Pentode

    Post by Bob Latino on Wed Nov 24, 2010 5:11 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

    ejc

    Posts : 32
    Join date : 2010-10-16
    Age : 65
    Location : Connecticut

    Re: Triode vs. Pentode

    Post by ejc on Wed Nov 24, 2010 2:07 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
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Triode vs. Pentode

    Post by Bob Latino on Wed Nov 24, 2010 3:02 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

    Disles1

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

    Re: Triode vs. Pentode

    Post by Disles1 on 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
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Triode vs. Pentode

    Post by Bob Latino on 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

    Sponsored content

    Re: Triode vs. Pentode

    Post by Sponsored content Today at 11:21 am


      Current date/time is Wed Dec 07, 2016 11:21 am