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    Triode/pentode switch question

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    xlr8

    Posts: 68
    Join date: 2010-02-09

    Triode/pentode switch question

    Post by xlr8 on Sun Feb 21, 2010 8:39 am

    Hello,

    I have been playing with 2 freshly rebuilt st-70's in a horizontal bi-amp configuration. I plan to go to vertical bi-amp and was wondering if it is safe to operate one channel in triode and the other in pentode. Any issues with this?

    Bob Latino
    Admin

    Posts: 1907
    Join date: 2008-11-27
    Location: Massachusetts

    Re: Triode/pentode switch question

    Post by Bob Latino on Sun Feb 21, 2010 9:22 am

    xlr8 wrote:Hello,

    I have been playing with 2 freshly rebuilt st-70's in a horizontal bi-amp configuration. I plan to go to vertical bi-amp and was wondering if it is safe to operate one channel in triode and the other in pentode. Any issues with this?

    xlr8,

    Yes - you can run one channel in pentode and the other in triode in a vertical biamp situation on either the ST-70 or ST-120. I have one customer who does just that in biamping with two ST-70's in his system. He uses the bass channel with KT88 tubes and the switch in pentode and the tweeter channel with KT77 tubes and the switch set in triode. Although you do lose some power with channel set in triode, he claims that he likes his system set up that way. See the link below on his biamp setup ...

    Biamping with two ST-70's

    One note - In the system at the link above he was horizontally biamping but at my suggestion he has now switched to vertical biamping with better (according to him) results. Explanation below ..

    Horizonatal biamping - You use one amp on the woofer of BOTH speakers and the other amp on the tweeter section of BOTH speakers.

    Vertical biamping - You use one amp on each stereo channel with one of the amp's channels on the woofer section and the other channel of the same amp on the tweeter section.

    Why is vertical biamping better if you use two ST-70 (or ST-120) tube amps to biamp?

    1. Greater signal isolation - there will be no crossover of a different musical signal from one channel of a stereo amp to the other since, in a vertical biamp situation, both channels of each stereo amp are carrying the SAME musical signal. The left stereo channel will be totally separated from the right stereo channel. The whole left stereo channel is on one amp while the whole right stereo channel is on the other amp. This is basically like a monoblock situation. Some listeners report hearing a greater sense of "space" in the music with a slightly larger soundstage in a vertical biamp setup.

    2. The power supplies of TWO amps will be able to handle the bass section. Bass sounds tax the power supplies of an amp much more than treble sounds. If you have just one amp handling the woofer sections of TWO speakers like in a horizontal biamp setup, you are overtaxing the power supply of that one amp while the other amp's power supply is loafing along just handling the two tweeter sections.

    IMHO it is always better to VERTICALLY biamp if you use two Dynaco stereo tube amps in your music system. That said, some people horizontally biamp with a big SOLID STATE amp on both woofer sections and a Dynaco tube amp on both tweeter sections - but that is a different situation.

    Bob

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