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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 10:39 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 : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Triode/pentode switch question

    Post by Bob Latino on Sun Feb 21, 2010 11:22 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

    TPW

    Posts : 7
    Join date : 2015-09-18

    ST-120 Triode mode is good, Pentode mode has pops and crackles

    Post by TPW on Wed Sep 30, 2015 8:42 pm

    Hi All! I'm new here and not new to the stereo gig (50+ years). I built a ST-120 in '12 and I love it. Recently I replaced the stock output tubes with Gold Lion KT88s and I do like them. Last night I turned the amp on and noticed a bit of hiss (white noise) on the left channel so I listened a while and it popped and crackled loudly a couple of times. The amp was in pentode mode so I switched it to triode mode and it hasn't done that since. I'm loath to put it back in pentode mode because the popping was pretty violent and I don't want to damage my new Sonus fabers! All suggestions will be appreciated.

    Kentley

    Posts : 295
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Triode/pentode switch question

    Post by Kentley on Wed Sep 30, 2015 10:30 pm

    First, try a careful cleaning of the tube pins and sockets. DeOxit products are the best way to accomplish this. Before you replace the tube(s), make sure you retension the sockets. Take a jeweler's screwdriver to each hole and crimp the contact slightly so that each pin fits snugly. My guess is that the contacts on the "bad" tube have become corroded. It's always a good idea to work the tube in and out of the socket on a regular basis.
    And every tube batch of every brand may have slightly different diameter pins. Retension and clean often.

    GreggW

    Posts : 55
    Join date : 2015-07-15

    Re: Triode/pentode switch question

    Post by GreggW on Thu Oct 01, 2015 12:46 am

    My ST120 is a '12 model, so I cleaned the tube sockets with a pipe cleaner and DeOxit, then retentioned the pins. I also cleaned the tube pins with DeOxit, couldn't hurt. Double check the solder connections on the triode/pentode switches...

    Kentley

    Posts : 295
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Triode/pentode switch question

    Post by Kentley on Thu Oct 01, 2015 1:42 am

    His Eminence Sir Jim McShane, one of the Expert Tubologists in the country, has repeatedly stated that upwards of 90% of all new tube "problems" are due to these simple maintenance issues. Caveat Tuber. {Beware the Potato???}.

    TPW

    Posts : 7
    Join date : 2015-09-18

    Re: Triode/pentode switch question

    Post by TPW on Thu Oct 01, 2015 8:10 pm

    Thank you for the useful advise! What DeOxit product do you folks use?

    Kentley

    Posts : 295
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: Triode/pentode switch question

    Post by Kentley on Thu Oct 01, 2015 8:24 pm

    I found the "DeoxIT Audio/Visual SURVIVAL KIT", which contains three or four cleaner/lube/protectants in various forms (i.e. spray, liquid and drops) plus a plethora of brushes, cloths, and applicators, to cover every possible contingency. It is available from Amazon:

    http://www.amazon.com/CAIG-LABORATORIES-SK-AV35-DEOXIT-SURVIVAL/dp/B00DKYPNU0/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1443745365&sr=1-2-catcorr&keywords=deoxit+survival+kit

    TPW

    Posts : 7
    Join date : 2015-09-18

    Re: Triode/pentode switch question

    Post by TPW on Fri Oct 02, 2015 3:15 pm

    Much thanks! Just ordered it.

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Triode/pentode switch question

    Post by sKiZo on Fri Oct 02, 2015 6:14 pm

    These are handy too ...



    (Just gooOOoogle "needle bottle". I got mine from a clock repair dealer when I got some like ... uh ... clock repair stuff.)

    I just spray a bit of D5 into one and dribble it here and there as needed. Gets around any overspray issues as you dribble it about, here and there. Doesn't take much either ... just a drop on a pipe cleaner or q-tip will go a long way.

    Not a bad idea to follow up with canned air as well. If you do it right, you shouldn't get any cleaner spraying out ... just loose odds and ends that can find their way into the strangest places.

    And remember folks ... BEWARE THE POTATO!!

    (think I'm gonna get the t-shirt)

    Dale Stevens

    Posts : 76
    Join date : 2014-07-06
    Age : 67
    Location : Loris, SC

    Re: Triode/pentode switch question

    Post by Dale Stevens on Sat Oct 03, 2015 10:08 am

    sK, good point. Those are the same bottles that are sold at the tobacco VAPE shops; used to refill an electronic cig and should be on the cheap. Dale

    sKiZo

    Posts : 1285
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Triode/pentode switch question

    Post by sKiZo on Sat Oct 03, 2015 1:39 pm

    Just be sure to label them well ... I don't expect you'll get the intended results if you were to, say ... spray muriatic acid into a tube socket ... affraid

    Which brings up another point ... haven't found anything yet the bottles won't stand up to, and I expect in this day and age, they're considered safer than using old syringes found in a back alley somewhere.

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