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    2 output tubes vs 4

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    LeGrace

    Posts : 126
    Join date : 2016-08-07

    2 output tubes vs 4

    Post by LeGrace on Thu Nov 03, 2016 9:19 am

    Recently took the big step of deciding to early retire. Some adjustments to spending habits will be necessary!

    That's the background story. Anyway, so this weekend I'm picking up some new to me Tannoy speakers. Sensitivity is spec'd at 93 db, 5 db more then my current speakers. I'm hoping this is enough that I can start running my M125's on only 2 output tubes. Once I factor in currency exchange, duty and VAT charges two quads of KT88's really add up. I will have a lot more time for listening (yay), but on the other hand it also means I'll be eating into tube life more quickly (boo) If I can get away with just 2 per amp servicing costs will be much more manageable.

    Anyone out there running their M125's on two for perhaps a similar reason? is 93 high enough to expect reasonable results?

    Bob Latino
    Admin

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    Location : Massachusetts

    Re: 2 output tubes vs 4

    Post by Bob Latino on Thu Nov 03, 2016 11:52 am

    Hi Legrace,

    If you do run just two output tubes per each M-125, I advise using the front two sockets. The two output tubes will be further away from the power transformer and will run a little cooler. You will get 65 watts per each monoblock. The amps set up like this and using 93 dB efficient speakers, should still have more power than you would need with plenty of headroom available for musical peaks.

    Bob

    sKiZo

    Posts : 1337
    Join date : 2013-04-01
    Location : Michigan USA

    Re: 2 output tubes vs 4

    Post by sKiZo on Thu Nov 03, 2016 3:01 pm

    Question

    Do you lose any dynamics or detail running half of a push/pull build? Seems to me that'd be mighty hard on the tubes, which I expect is why you pointed out potential heating issues.

    Bob Latino
    Admin

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    Re: 2 output tubes vs 4

    Post by Bob Latino on Thu Nov 03, 2016 3:25 pm

    sKiZo wrote: Question

    Do you lose any dynamics or detail running half of a push/pull build? Seems to me that'd be mighty hard on the tubes, which I expect is why you pointed out potential heating issues.

    You will lose about 3 dB of headroom on musical peaks by going from the 4 output tube mode to the 2 output tube mode on the M-125's. Whether you notice the loss of headroom is a question that would be more difficult to answer ?

    Bob

    10-E-C

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    Join date : 2014-02-12
    Age : 63
    Location : upper east tn

    Re: 2 output tubes vs 4

    Post by 10-E-C on Thu Nov 03, 2016 3:33 pm

    LeGrace wrote:Recently took the big step of deciding to early retire. Some adjustments to spending habits will be necessary!

    That's the background story. Anyway, so this weekend I'm picking up some new to me Tannoy speakers. Sensitivity is spec'd at 93 db, 5 db more then my current speakers. I'm hoping this is enough that I can start running my M125's on only 2 output tubes. Once I factor in currency exchange, duty and VAT charges two quads of KT88's really add up. I will have a lot more time for listening (yay), but on the other hand it also means I'll be eating into tube life more quickly (boo) If I can get away with just 2 per amp servicing costs will be much more manageable.  

    Anyone out there running their M125's on two for perhaps a similar reason? is 93 high enough to expect reasonable results?

    I run only two output tubes in my M125's, (KT120s)  my speakers are rated at 99 db. I can't tell any difference in two or four tubes, but my listening area is a little small.

    LeGrace

    Posts : 126
    Join date : 2016-08-07

    Re: 2 output tubes vs 4

    Post by LeGrace on Thu Nov 03, 2016 3:52 pm

    99 db is really high, no wonder you don't hear any difference. Are they Klipsch horns?

    sKiZo

    Posts : 1337
    Join date : 2013-04-01
    Location : Michigan USA

    Re: 2 output tubes vs 4

    Post by sKiZo on Thu Nov 03, 2016 4:00 pm

    Running 89db efficiency here ... I believe using the word "efficiency" is a bit of a misnomer in my case.

    That said, I plan on being buried with my McIntosh XR16's ... hellfire, I could be buried IN them.

    10-E-C

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    Age : 63
    Location : upper east tn

    Re: 2 output tubes vs 4

    Post by 10-E-C on Thu Nov 03, 2016 7:00 pm

    LeGrace wrote:99 db is really high, no wonder you don't hear any difference. Are they Klipsch horns?


    They are Zu Audio Omen Definitions, full range speakers (two 11 inch speakers) with a tweeter. no crossovers but one cap to roll off the low frequencies to the tweeter.

    Kentley

    Posts : 359
    Join date : 2015-03-06
    Age : 64
    Location : Worcester, MA

    Re: 2 output tubes vs 4

    Post by Kentley on Thu Nov 03, 2016 10:56 pm

    LeGrace {great name -c'est vrai!} - I think a bit of perspective might put ton ame at rest.
    The decibel scale is somewhat misleading, in that it's a logarithmic scale. That means that every increase represents a yooge increase. Without going into the mathy details, a "90 db efficiency" rating effectively "costs" way less than a 93 db rating. We're talking half the energy or so.
    I just jumped from a 90 db rated speaker to an 88, with the ST-120 (which is effectively equivalent to the M-125s driven with two output tubes.)
    After dealing with the issue of tired tubes (read elsewhere) I STILL have the ability to blow the windows out - of my neighbor's house - with crystal clear nuclear force. Your Tannoys are capable of FOUR TIMES the sound pressure level with the same 60 watts per. Worry not. Tu est d'or. Or something like that.... santa

    LeGrace

    Posts : 126
    Join date : 2016-08-07

    Re: 2 output tubes vs 4

    Post by LeGrace on Fri Nov 04, 2016 7:19 am

    10-E-C wrote:
    LeGrace wrote:99 db is really high, no wonder you don't hear any difference. Are they Klipsch horns?
    They are Zu Audio Omen Definitions, full range speakers (two 11 inch speakers) with a tweeter. no crossovers but one cap to roll off the low frequencies to the tweeter.

    Cool, quickly scanned a couple reviews. Somewhat similar design concept to the Tannoys (two 10 inch speakers). Both differing a lot from my Polks. The Polks will join my 7.1 AV setup as front speakers, a big upgrade for this system.

    In terms of my stereo setup the driver approach of the Tannoys and Zus of the world seems like a more natural approach to sound reproduction, versus the multi driver take the sound apart and put it back together approach common in so many designs today. Certainly was an important factor in choosing these as opposed to something else.    

    And thanks Kentley for your comments, certainly helps put my mind at ease!

    bluemeanies

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    Join date : 2015-02-09
    Age : 66
    Location : Folsom Pa.

    Re: 2 output tubes vs 4

    Post by bluemeanies on Sun Nov 06, 2016 8:26 pm

    I have the m125's with four KT88's and the Mullard GZ34 in a room that is 25' long, two widths 8'-10' with two ceiling heights 6'3"-7'...speaker B&W803Diamonds.
    The room is filled with music....
    The other side of the coin is that I feel the same way with two KT88's....the difference between the two IMO was the headroom with four output tubes.
    The bass, sonics, tonal qualities and life like performance are sublime with both setups. I cannot say that I won't go back to two KT88's
    Just wanted to mention my experience.

    LeGrace

    Posts : 126
    Join date : 2016-08-07

    Re: 2 output tubes vs 4

    Post by LeGrace on Mon Nov 07, 2016 2:49 pm

    Thanks for all the help!

    deepee99

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    Re: 2 output tubes vs 4

    Post by deepee99 on Mon Nov 07, 2016 3:24 pm

    It does depend on speaker efficiency. As Kentley has mentioned, dB is a logarithmic measurement. If your speakers are in the 90 dB area (as are mine) just the two tubes out front will do the trick for all but the largest rooms. Generally, in the summer I just use the two front holes; in the winter when the house needs heat, I'll fill the two back sockets, too.
    There are also budgetary considerations. Two tubes in each M-125 will last twice as long as four tubes, because the omitted pair are in their boxes. So if your funds are constrained, just run two tubes (in the front sockets) of each amp. Again, I'm assuming you aren't trying light up the whole neighbourhood, and that your speaks are in the 90 dB range.
    Also, experiment with bias. You may want to up it a tad if you're just using the front pair. Start with .4v/tube (.8VDC on the pot) and crank it up to .55VDC/tube (1.1 on the pot), see what sounds best. The age of your tubes, ranging from antique Tung-Sols to modern re-issue Gold Lion KT-88s
    is also a factor. The old guys like a little lower setting.



    LeGrace

    Posts : 126
    Join date : 2016-08-07

    Re: 2 output tubes vs 4

    Post by LeGrace on Mon Nov 07, 2016 3:47 pm

    Wasn't even aware of the voltage marker numbers on the top of the pots! Just looked and I see them. Coarse indication at best however. Speakers are 93 db and seem to be quite content on just 2 output tubes.

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