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    M125 anniversary look back

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    LeGrace

    Posts : 233
    Join date : 2016-08-07
    Location : Ontario, Canada

    M125 anniversary look back

    Post by LeGrace on Mon Sep 11, 2017 3:36 pm

    Elation all the way through to despair about describes it. Today am enjoying them greatly, but it wasn't always sunshine. I started out with zero knowledge of tube amps, just dove right in. What a difference a year makes!  

    I remember the sense of relief when I first turned them on and they worked! A high five for the very detailed and clear instructions. But I was downtrodden a week later when I flipped the switch, saw an arc flash, and one of the amps died. At that point I had no idea why. Just knew that I had spent a fair bit and one was already broken. This became my first lesson, actually two lessons. First one being M125's devour 5AR4's, secondly when it comes to tube amps, panic slowly! (and keep lots of spare fuses on hand) Because 3 weeks later it happened again! Panic attack! But with great help from this forum I learned about the yellow sheet diode mod and stouter rectifier options. (such as GZ37's!)

    So I'm thinking I'm good now after about 6 months of stable operation post diode mod. Wrong, the amps weren't done with me yet. Next a power tube goes. Tube will still fairly new and mainly I was feeling ripped off. But then I experience two red plate events in succession. confused Then another power tube goes. Paranoia ensues! Well all of it boiled down to crappy power tubes! Installed new ones recently and talk about an improvement. Bias used to swing all over but is now stable. Another lesson, stick to reputable tube outfits!

    Meanwhile through all of this I'm also experiencing varying levels of amplifier hum. Funny at first it didn't bother me much, but as I invested more and more into my audio system it really started to get on my nerves. My amps are dead quiet now, but I had to resort to cheater plugs. Currently looking for a safer solution and if I find one will definitely share.

    So finally my amps are  silent, they sound amazing, and they are stable. If you have just built a pair of these fantastic amps, are just getting into tubes like I was, then hopefully some of this can save you repeating some of the mistakes I made. FWIW.
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    corndog71

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    Re: M125 anniversary look back

    Post by corndog71 on Mon Sep 11, 2017 5:49 pm

    My first tube amp story went pretty much the same way. I picked up a used and rebuilt ST70 from a local hifi store and learned just about every which way things can go wrong. I went through lots of cheap rectifiers and power tubes. This was about 13 years ago. Since then I've built and rebuilt several tube amps and it never gets old. The simplicity, flexibility and sonic bliss were all factors with channeling my energy into these.
    Just wait until you see what I'm cooking up next!

    costerdock

    Posts : 35
    Join date : 2011-07-27

    Re: M125 anniversary look back

    Post by costerdock on Thu Sep 28, 2017 11:54 am

    As I posted in the other thread - I use humX devices (2) - work perfectly - much safer than cheater plugs.

    I also started out with some issues - learned from them - I've now replaced my original sovtek 88s with Gold Lions.  I was able to get 6 years out of the sovteks.   I've always kept my bias below 1.2 and below .6 and that has allowed me to keep the same rectifiers for years.  I haven't done the mod you are talking about - and perhaps will.  The new lower bias settings are now inline with what I've been using.  ex .5 for two tube setup - which I now prefer.
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    LeGrace

    Posts : 233
    Join date : 2016-08-07
    Location : Ontario, Canada

    Re: M125 anniversary look back

    Post by LeGrace on Thu Sep 28, 2017 3:32 pm

    Thanks, I'll look into humX. 6 years is really impressive! (assuming regular usage)
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    Bob Latino
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    Location : Massachusetts

    Re: M125 anniversary look back

    Post by Bob Latino on Thu Sep 28, 2017 4:52 pm

    costerdock wrote:I was able to get 6 years out of the sovteks.

    Unfortunately Sovtek stopped making their KT88's a few months ago. After a month of testing Sovtek's 6550WE output tubes here, I found that their 6550 output tubes are every bit as good as their KT88's with respect to sound quality and durability. All the VTA ST-120 and M-125 kit or wired amp customers that want a tube set with their amps now get shipped a matched quad (ST-120) or a matched octet (M-125) of the Sovtek 6550 output tubes. 6550's are about the same height as a KT88 but are straight walled tubes. They maybe don't look as "cool" as the coke bottle shaped KT88's but they do perform well. The Sovtek's are only about $28 - $32 each which is modestly priced compared to other 6550 or KT88 output tubes. The VTA ST-120 amp review from Home Theater and Hi-Fi below was with the standard VTA tube set with a matched quad of Sovtek 6550's.

    VTA ST-120 amp review using Sovtek 6550 output tubes

    Bob

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    deepee99

    Posts : 1759
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: M125 anniversary look back

    Post by deepee99 on Sat Oct 07, 2017 3:38 pm

    Bob Latino wrote:
    costerdock wrote:I was able to get 6 years out of the sovteks.

    Unfortunately Sovtek stopped making their KT88's a few months ago. After a month of testing Sovtek's 6550WE output tubes here, I found that their 6550 output tubes are every bit as good as their KT88's with respect to sound quality and durability. All the VTA ST-120 and M-125 kit or wired amp customers that want a tube set with their amps now get shipped a matched quad (ST-120) or a matched octet (M-125) of the Sovtek 6550 output tubes. 6550's are about the same height as a KT88 but are straight walled tubes. They maybe don't look as "cool" as the coke bottle shaped KT88's but they do perform well. The Sovtek's are only about $28 - $32 each which is modestly priced compared to other 6550 or KT88 output tubes. The VTA ST-120 amp review from Home Theater and Hi-Fi below was with the standard VTA tube set with a matched quad of Sovtek 6550's.

    VTA ST-120 amp review using Sovtek 6550 output tubes

    Bob


    Great review, but I do have a problem with:
    "Nothing much to this – plug in the tubes (they’re keyed only go in one way, so you can’t mess it up), set the output tube bias (a multimeter & small screwdriver will be required), hook up the speakers & inputs, turn it on – and instant music!"
    Sequence should be speakers hooked up first, turn the amp(s) on, then set the bias. Then shut down, power-up the preamp and peripherals. Turn the latter on first and then re-power the amps. I know, picky-picky-picky. Unless there's something I don't know about setting bias with the power off...


    Last edited by deepee99 on Sun Oct 08, 2017 1:40 pm; edited 1 time in total

    Dogstar

    Posts : 287
    Join date : 2014-06-23

    Re: M125 anniversary look back

    Post by Dogstar on Sun Oct 08, 2017 1:22 pm

    Bob Latino wrote:
    costerdock wrote:I was able to get 6 years out of the sovteks.

    Unfortunately Sovtek stopped making their KT88's a few months ago. After a month of testing Sovtek's 6550WE output tubes here, I found that their 6550 output tubes are every bit as good as their KT88's with respect to sound quality and durability. All the VTA ST-120 and M-125 kit or wired amp customers that want a tube set with their amps now get shipped a matched quad (ST-120) or a matched octet (M-125) of the Sovtek 6550 output tubes. 6550's are about the same height as a KT88 but are straight walled tubes. They maybe don't look as "cool" as the coke bottle shaped KT88's but they do perform well. The Sovtek's are only about $28 - $32 each which is modestly priced compared to other 6550 or KT88 output tubes. The VTA ST-120 amp review from Home Theater and Hi-Fi below was with the standard VTA tube set with a matched quad of Sovtek 6550's.

    VTA ST-120 amp review using Sovtek 6550 output tubes

    Bob


    After reading Bob's announcement about Sovtek not making KT-88's any longer I navigated to the TubeDepot.com web site to see what other companies make 6550's and noticed that Tung Sol also seems to not make KT-88's but they are supposedly offering a coke bottle shaped 6550 tube. I'm pretty sure I had seen that TungSol made KT-88's in the past but I only have TungSol 12AU7's and KT-120's.
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    deepee99

    Posts : 1759
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: M125 anniversary look back

    Post by deepee99 on Sun Oct 08, 2017 1:50 pm

    costerdock wrote:As I posted in the other thread - I use humX devices (2) - work perfectly - much safer than cheater plugs.

    I also started out with some issues - learned from them - I've now replaced my original sovtek 88s with Gold Lions.  I was able to get 6 years out of the sovteks.   I've always kept my bias below 1.2 and below .6 and that has allowed me to keep the same rectifiers for years.  I haven't done the mod you are talking about - and perhaps will.  The new lower bias settings are now inline with what I've been using.  ex .5 for two tube setup - which I now prefer.

    IIRC, Bob L. not long ago recommended 1.1 (.55/tube) for the M-125s. I found the reduced settings changed absolutely nothing sound-wise and takes a bit of stress off everything. Tube guru Andy Bowman recommends, if you're using new vintage TS 6550s or Brit KT-88s, starting bias at .45/tube given the VTAs' plate voltages and work very slowly up from there to maybe .5.
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    Bob Latino
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    Posts : 2578
    Join date : 2008-11-26
    Location : Massachusetts

    Re: M125 anniversary look back

    Post by Bob Latino on Sun Oct 08, 2017 3:11 pm

    deepee99 wrote:

    IIRC, Bob L. not long ago recommended 1.1 (.55/tube) for the M-125s.

    The current recommended bias setting for the M-125's is 1.00 VDC for each side which give a bias current of 50 milliamps per each output tube.

    Bob
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    deepee99

    Posts : 1759
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: M125 anniversary look back

    Post by deepee99 on Sun Oct 08, 2017 3:16 pm

    Bob Latino wrote:
    deepee99 wrote:

    IIRC, Bob L. not long ago recommended 1.1 (.55/tube) for the M-125s.

    The current recommended bias setting for the M-125's is 1.00 VDC for each side which give a bias current of 50 milliamps per each output tube.

    Bob
    I stand corrected, good Sir. I remembered you had lowered them from 0.6. 0.5 works for me.

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