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    Tube store tube number

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    ValleySounds

    Posts : 20
    Join date : 2012-09-25
    Location : Calgary, Ab

    Tube store tube number

    Post by ValleySounds on Thu Oct 24, 2013 2:27 am

    I have a question about The Tube Store matching and numbers they put on their tubes.
    I know they match their tubes by measuring plate current draw.

    I have a Latino ST-120 and am going to purchase a new set of KT120'S from The Tube Store.
    Does anyone have any suggestions on what would be a good number to request from them for this amp.
    My current tubes are kt88's with a 44 number on them.

    I know the ST-120 has a large range to bias but I have had trouble with another amp in the past getting a number that was too high and I could not get it bias down to a safe range.

    Thanks,



    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Tube store tube number

    Post by peterh on Thu Oct 24, 2013 3:35 am

    ValleySounds wrote:I have a question about The Tube Store matching and numbers they put on their tubes.
    I know they match their tubes by measuring plate current draw.

    I have a Latino ST-120 and am going to purchase a new set of KT120'S from The Tube Store.
    Does anyone have any suggestions on what would be a good number to request from them for this amp.
    My current tubes are kt88's with a 44 number on them.

    I know the ST-120 has a large range to bias but I have had trouble with another amp in the past getting a number that was too high and I could not get it bias down to a safe range.

    Thanks,


    Don't care about their numbers, make them select tubes that are matched in Gm and bias at 450V ( the operating
    voltage of your amp).
    Any decent tubes will then be able to bias in your vta-120.

    Jim McShane

    Posts : 154
    Join date : 2011-10-19
    Location : South Suburban Chicago

    Re: Tube store tube number

    Post by Jim McShane on Thu Oct 24, 2013 9:16 am

    peterh wrote:
    ValleySounds wrote:I have a question about The Tube Store matching and numbers they put on their tubes.
    I know they match their tubes by measuring plate current draw.

    I have a Latino ST-120 and am going to purchase a new set of KT120'S from The Tube Store.
    Does anyone have any suggestions on what would be a good number to request from them for this amp.
    My current tubes are kt88's with a 44 number on them.

    I know the ST-120 has a large range to bias but I have had trouble with another amp in the past getting a number that was too high and I could not get it bias down to a safe range.

    Thanks,


    Don't care about their numbers, make them select tubes that are matched in Gm and bias at 450V ( the operating voltage of your amp).  
    Any decent tubes will then be able to bias in your vta-120.
    First off, you aren't going to "make them" do anything like that. Even for a small vendor like me it's nearly impossible to "custom match" like that. Second, matching by plate current only is not nearly as good as matching by cathode current. Why? See here: http://www.audioasylum.com/audio/tubes/messages/25/253369.html

    I match KT-120s and most other large octal power tubes (after a minimum of 24 hours run) in at 465 volts on the plate and screen with -50 on the grid. I selected that point because it is right in the area where most of these tubes operate in the real world. I also match for Gm (transconductance).

    I applaud Bob Latino for providing an amp with a good, wide range of bias adjustment. Since cathode current can vary by 100% or more in any given tube number, it is important that either the tube seller know what bias range tubes work well in the amp - or that the amp can accept a wide biasing range of tubes. For example, I have KT-120s on hand that have bias currents ranging from the mid 80 ma range to 135 ma. - measured as mentioned above. Some of that is variance in plate current, some is variance in screen current - but it all can be seen in the cathode current - which is why that is a far better way to match for bias current. DO look at the link i posted!

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Tube store tube number

    Post by corndog71 on Thu Oct 24, 2013 9:50 am

    I would recommend RAM Labs for this kind of investment.  http://www.tubeaudiostore.com/powertubes.html

    and for some more good reading - The Virtues of Power Tube Matching

    They recommend 40-60mA bias current.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Tube store tube number

    Post by peterh on Thu Oct 24, 2013 1:13 pm

    Jim McShane wrote:
    peterh wrote:
    ValleySounds wrote:I have a question about The Tube Store matching and numbers they put on their tubes.
    I know they match their tubes by measuring plate current draw.

    I have a Latino ST-120 and am going to purchase a new set of KT120'S from The Tube Store.
    Does anyone have any suggestions on what would be a good number to request from them for this amp.
    My current tubes are kt88's with a 44 number on them.

    I know the ST-120 has a large range to bias but I have had trouble with another amp in the past getting a number that was too high and I could not get it bias down to a safe range.

    Thanks,


    Don't care about their numbers, make them select tubes that are matched in Gm and bias at 450V ( the operating voltage of your amp).  
    Any decent tubes will then be able to bias in your vta-120.
    First off, you aren't going to "make them" do anything like that. Even for a small vendor like me it's nearly impossible to "custom match" like that. Second, matching by plate current only is not nearly as good as matching by cathode current. Why? See here: http://www.audioasylum.com/audio/tubes/messages/25/253369.html

    I match KT-120s and most other large octal power tubes (after a minimum of 24 hours run) in at 465 volts on the plate and screen with -50 on the grid. I selected that point because it is right in the area where most of these tubes operate in the real world. I also match for Gm (transconductance).

    I applaud Bob Latino for providing an amp with a good, wide range of bias adjustment. Since cathode current can vary by 100% or more in any given tube number, it is important that either the tube seller know what bias range tubes work well in the amp - or that the amp can accept a wide biasing range of tubes. For example, I have KT-120s on hand that have bias currents ranging from the mid 80 ma range to 135 ma. - measured as mentioned above. Some of that is variance in plate current, some is variance in screen current - but it all can be seen in the cathode current - which is why that is a far better way to match for bias current. DO look at the link i posted!
    Aggree, cathode current is the way to go, i was unclear about this.

    Matching for simular bias AND Gm is what i want. That's what i do. So i guess we have the same way of "doing it".

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Tube store tube number

    Post by sKiZo on Thu Oct 24, 2013 6:02 pm

    Jim McShane wrote:I applaud Bob Latino for providing an amp with a good, wide range of bias adjustment.
    +1 ... Not to mention an easy way of doing it ...



    As far as the Tube Store numbers go, long as they match, you're golden. Only complaint I had about a set of KT120's I got from them was the big blue stickers they slapped onto those pretty chrome bases. Wrote an email asking how to get their silly stickers off the tubes? They wrote back, "We don't have silly stickers." To which my reply was, "So, how do I get the stickers off your silly tubes??"

    (I probably got lucky and ran into the dude who designed the silly stickers in the first place) tongue 

    Short version ... use a heat gun or blow dryer ... they peel right off then. Just stick them on the boxes for reference.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Tube store tube number

    Post by tubes4hifi on Thu Oct 24, 2013 6:14 pm

    I agree with Jim on this, and want to add that the best tube tester I've ever found is my own VTA70 amplifier.
    I've bought and sold 4 tubes testers over the past ten years, dont' need them.
    I can tell at a glance how close the tubes are, and 90% of the time just buying a set of unmatched tubes and putting them in the amp,
    they are usually within 5-10%, on the other hand, sometimes you get an odd tube that is 20-30% off from the others.
    Buying a matched pair or quad is easy and cheap, but you can also do your own tube matching with the amp.
    Just install the tubes, and watch where the bias pots end up at once you've got the cathode bias readings matched.
    If you're a "numbers" person and you need a number, once they are matched for bias reading, just go ahead and read the grid voltage off the output cap that goes to that tube.
    Then you'll know the plate voltage (the amp B+, which in the VTA70 is around 420vdc), the grid voltage (usually around -40vdc), and the cathode bias (0.400vdc recommended).
    And it never hurts to buy an extra tube or an extra pair of tubes. Out of six tubes I'd be amazed if you didn't find 4 that were a near perfect match.

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Tube store tube number

    Post by sKiZo on Fri Oct 25, 2013 12:10 am

    Do you have to let cryogenic tubes thaw out before testing them? scratch 

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: Tube store tube number

    Post by mantha3 on Fri Oct 25, 2013 7:24 am

    I go to TCTUBES.com

    Tell them what you want and they deliver

    Captain Coconut

    Posts : 213
    Join date : 2009-10-13
    Age : 64
    Location : Great White North

    Re: Tube store tube number

    Post by Captain Coconut on Fri Oct 25, 2013 3:17 pm

    I once bought a quad of EL84's from the Tube Store where three were closely matched and the fourth was way off. They said the "odd" one was probably disturbed during shipping. Since I had them past the 90 day warranty period, I couldn't return them. They had been sitting around for 5 months before I used them, but too bad, 90 days were up. Then I discovered Jim, and bought a quad from him - they are still matched within 1.5% a year and a half later.

    I don't think the Tube Store is diligent enough with their testing.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Tube store tube number

    Post by tubes4hifi on Fri Oct 25, 2013 6:10 pm

    I primary use TubeDepot and Jim McShane for tube purchases. Always keep your receipt and your tube boxes for at least 90 days.
    I've only had to return 3-4 tubes in the past two years, but NEVER had any problem with getting a replacement within that time period.

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: Tube store tube number

    Post by mantha3 on Fri Oct 25, 2013 7:13 pm

    www.TCTUBES.com operates out of the Minneapolis / St Paul area. It is ran by a husband and wife. Call them and talk to Tyler about what you are looking for in the tubes. They have 100s of KT120 tubes and test each and every one on an amplitrex at1000 digital tester.

    If you have specific test #s you are looking for in a quad of KT120s they would do that for you. I have had them do that for me. I have been to the home of the owners and they are excellent to do business with.


    ruffian

    Posts : 43
    Join date : 2010-02-26

    Re: Tube store tube number

    Post by ruffian on Sat Oct 26, 2013 2:18 am

    tubes4hifi wrote:I primary use TubeDepot and Jim McShane for tube purchases.   Always keep your receipt and your tube boxes for at least 90 days.
    I've only had to return 3-4 tubes in the past two years, but NEVER had any problem with getting a replacement within that time period.
    The only time that I have returned tubes to Jim was the time he sent me someone elses order by mistake. We are not always perfect but Jim is top notch.

    ValleySounds

    Posts : 20
    Join date : 2012-09-25
    Location : Calgary, Ab

    Re: Tube store tube number

    Post by ValleySounds on Sat Oct 26, 2013 11:25 am

    Thanks for the info guys.

    I like to use The Tube Store because they are located in Canada like me. No duties or cross border shipping hassles. So far they have been great to me for customer service. I ordered a EHKT-88 quad from them that didnt work in my amp (too much current draw to bias properly). I figured it was my amp and not the tubes. I put my old 6550 back in the amp and let the new tubes sit on the shelf for 8 months while I tried to build more knowledge into this whole tube thing. Long story short they took them back no problems and exchanged them for the proper tubes after more then half a year.

    There seems to be quite a number of tube venders out there. I will do some research and see if any of the Canadian companies are matching the cathode current. There are 3 companies up here that I have purchased from and will ask them all some questions.
    The Tube Store
    Parts Connexion
    Grant Fidelity

    Thanks again for helping out.

    Steve

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