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    M-125 Two tubes, or four?

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    LeGrace

    Posts : 218
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: M-125 Two tubes, or four?

    Post by LeGrace on Sun Mar 19, 2017 7:33 pm

    deepee99 wrote:I have heard no difference between a pair and a quad of KT-88s in my M-125s, but I have reasonably efficient (91 dB) speakers so maybe no need for the extra headroom. Too many other variables to consider, too, i.e. room size and acoustics, etc.
    Interestingly, the drop in rated watts is about the same going from ultralinear to triode mode with four tubes as it is with two tubes in ultralinear. Anyone made that comparison?

    This is where I have been noticing a difference. I prefer triode mode, but my room is quite large. So I found I needed to put the amps in UL mode for SPL, etc reasons. Now I'm back even on a power level basis as I was with the 2 on UL, but I still find more depth and smoothness despite the power being equivalent. Probably the mode.
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    deepee99

    Posts : 1696
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: M-125 Two tubes, or four?

    Post by deepee99 on Sun Mar 19, 2017 7:40 pm

    LeGrace wrote:They run fine either way, but such a waste not to be using them to their full capability.

    Reason I ask Steve I was a total tube newb when I started out. Main advice is do the yellow sheet mod right out of the gate. (ref diodes on the rectifier socket, see the sticky titled tube rectifier diode mod) I blew several rectifiers until I found out about this. Second buy good quality tubes from a reputable outfit. (ref my loose socket thread) Then enjoy! Keep us posted how things go.

    Excellent advice from LeGrace. Also, get the TDR (time-delay relay) option for $35 each, which can be installed during or after you've built the amps. These allow the filaments to heat up the tubes for ~15 seconds before the high B+ voltage kicks in. This will save your output tubes considerable stress at start-up. And plug everything into a 15-amp MANUAL RESET ground-fault current interrupter (GFCI) for about $20 to protect you from sudden on-off-on blips from the wall socket that can crash a rectifier (or worse). Make sure it's a manual-reset.


    Steve G

    Posts : 15
    Join date : 2017-03-17
    Location : Carson City, NV

    Re: M-125 Two tubes, or four?

    Post by Steve G on Mon Mar 20, 2017 2:58 pm

    I have one octet of KT-88's on the way, go big or go home. I know I wanted a full complement of tubes and after they burn in I may try it with two just to hear what they sound like.
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    LeGrace

    Posts : 218
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: M-125 Two tubes, or four?

    Post by LeGrace on Mon Mar 20, 2017 3:34 pm

    I ran two out of necessity and its a great fall back in the event of a tube failure. Each must decide.

    Steve G

    Posts : 15
    Join date : 2017-03-17
    Location : Carson City, NV

    Re: M-125 Two tubes, or four?

    Post by Steve G on Mon Mar 20, 2017 5:02 pm

    LeGrace wrote:I ran two out of necessity and its a great fall back in the event of a tube failure. But its definitely not the same. Each must decide.

    That's a good idea. Knowing how I am the empty sockets would drive me crazier.

    zx

    Posts : 197
    Join date : 2011-08-05

    Re: M-125 Two tubes, or four?

    Post by zx on Wed Mar 22, 2017 4:24 pm

    Older 1960 hhscott tube amps preamps, always been one the best tube sounds I have ever heard...
    One thing hhscott did was ran there heaters low....its even own there schematic ..small input tubes...5.7...output tubes 6.1..
    I have setup some Diy tube preamps with lower heaters 5.7-6.an I have found it has a sweeter sound..fuller tone..like with the Big Tone of 6SN7s
    I have found one of the biggest sound killers with newer tube amps preamps is High heaters ..6.8-7.3.
    I see know way that if-when you pull 2 output tube out of any tube amps output setup to run 4...that the heaters Volts well not rise....
    I am not saying pulling 2 of the output tube well sound bad...an this cant be done, we all know it can...an it well not damage the amps in anyway.....but for sure it well change the sound !
    I would think it would be hard to compare...sounds

    This is just one man finding



    thanks for the site Bob...................

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