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    New tube combos help on VTA70 mod

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    Bigron865

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    New tube combos help on VTA70 mod

    Post by Bigron865 on Sun Mar 17, 2013 10:52 pm

    Hello all, just finished my vta 70 classic mod. Thanks to Bob for helping me with some newb mistakes. Started with sovtek el34s and a trio of JJ 12AU7s. I'm a little disappointed in the soundstage/bass and hi mids seem harsh right now. I'm hoping a tube swap will do the trick. I have been using a Sweet little 6v6 Stromberg Carlson ASR120. Maybe I'm just not used to the el's yet? Anyway...
    I ordered a quad of EH6CA7's for output and I have 2 RCA clear top 12AU7's on order (orange lettering) as well as 3 nos RCA long plate 5814A's and 2 GE 5814a's.
    What can I expect with all of these options and where should I start? All RCA, GE or mix them up?

    Bigron

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Mon Mar 18, 2013 12:10 pm

    BTW..I don't have a tube pre yet. Still using an NAD1600 SS pre. I'm hoping to get my hands on a PAS3 soon and try the TUBES4HIFI mods. How much difference can I expect with a PAS2 or 3 vs. the NAD? I'm using Klipsch RB61II refrerece speakers and all vinyl through a Thorens TD-160. So excited to be a part of the Tube World now!

    hawaii.ken

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    Re: New tube combos help on VTA70 mod

    Post by hawaii.ken on Mon Mar 18, 2013 1:12 pm

    If you're using PIO caps you might want to use the amp for while before doing any tube rolling. PIO caps take a while to "break-in".

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Mon Mar 18, 2013 1:26 pm

    I'm using the classic vta. Didn't go for the attenuators upgrade yet. The 6v6 SC I've had for a while just sounds more sparkley and wider soundstage. We'll see how the new tubes do for the vta70 mod. Thanks for replying!

    charlief64

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    Re: New tube combos help on VTA70 mod

    Post by charlief64 on Mon Mar 18, 2013 10:31 pm

    I think I'm quoting Mr. Latino here ... the center tube in the driver board can make a world of difference. I started with JJ's too, then I put in a trio of new Gold Lions and almost couldn't believe how much they improved the soundstage and highs and lows.
    charlie

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Mon Mar 18, 2013 10:43 pm

    Thanks Charlie. I'm excited about the new/old tubes that are on their way. I read several reviews about the EH6ca7 tubes so I ordered some of those too. Should have a whole new sound by the weekend!

    tubes4hifi
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    Re: New tube combos help on VTA70 mod

    Post by tubes4hifi on Tue Mar 19, 2013 1:09 am

    personally I love the big 6CA7s and the clear-top RCAs, but not saying that's the best combo, as I haven't tried alot of different tubes.
    BTW, a tube preamp will make even a bigger difference in your system than a tube amp does. It's like 4D instead of 3D ! Wink

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Tue Mar 19, 2013 12:56 pm

    Thanks for the reply. THAT 4D SOUND is what im after!!!
    Anyone know where I could look for a PAS2 or 3 other than *bay or Craigslist? I'd love to have one and start the upgrade project. BUT as most everyone else, I have limited funds since upgrading the ST70. Seems like they are sparce or too expensive on *-bay right now.

    tubes4hifi
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    Re: New tube combos help on VTA70 mod

    Post by tubes4hifi on Tue Mar 19, 2013 1:19 pm

    I like to remind everyone that if you want to buy a PAS3 only to totally mod it out, it's a waste of your money.
    You can buy a PAT4 on ebay for around $50-75, totally gut it out, then fill it up with the same exact PAS3 mods.
    Doing this saves you about $200 over doing the same thing to a PAS3.

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Tue Mar 19, 2013 1:27 pm

    Wow. that sounds great. I'll check it out. Thanks for the advice!

    Bob Latino
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    Re: New tube combos help on VTA70 mod

    Post by Bob Latino on Tue Mar 19, 2013 3:06 pm

    I agree completely with Roy. The PAS preamps require heavy modification to really sound good and when you heavily modify a PAS preamp - even though it will sound much better - you will devalue the preamp should you ever decide to sell it. If the best sound with a VTA amp (or any amp for that matter) is your objective, you are better off to do what Roy mentioned OR just sell the PAS preamp and use the money obtained to fund the purchase of one of Roy's SP series of preamp kits. See link below ..

    Tubes4hifi preamp kits ...

    Bob

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Tue Mar 19, 2013 6:08 pm

    Makes sense. Maybe I'll go that route.
    Just got my rca 5814a trio, a psi of RCA clear top 12au7's and a pair of GE jrc 5814a's. I have the trio of RCA in right now. Sounds better. Can I put any of these in the center position with a match on the others or does it even matter?

    tubes4hifi
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    Re: New tube combos help on VTA70 mod

    Post by tubes4hifi on Tue Mar 19, 2013 6:15 pm

    the two side tubes should match, the one in the center operates on both channels

    Bob Latino
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    Re: New tube combos help on VTA70 mod

    Post by Bob Latino on Tue Mar 19, 2013 6:21 pm

    What Roy has said is quite true .. keep the two side tubes the same ...

    Tubes that I have tried in all three positions are > 12AU7, 12BH7, 5814, 5963, 6189 and the Mullard CV4003. All work well.

    Bob

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Tue Mar 19, 2013 6:32 pm

    Ok great. I just put one of the RCA clear tops in the center and seemed to get a little more separation and warmer vocals but it could be in my head. I still have the old Sovteks el84 in the output. The EH6CA7's won't be here till Friday. Maybe those will help too. I'm missing that 6v6 sound I had with the Stromberg Carlson but the bass on this vta70 is much tighter. Looking for that upper sparkle.

    Andy Jersey

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    Re: New tube combos help on VTA70 mod

    Post by Andy Jersey on Sat Mar 23, 2013 1:23 pm

    Just eleaborating on driver tube choices. First Ken and Bob are right PIOs take time to breakin. If you start rolling now you're chasing a moving target. I liked a tele au7 in the middle there is an oddball raytheon that sound similar (i don't remember the #) I've found BH7s sound better in the outside positions. I'm running KT120s in mine and then speakers, ears room acoustics make up a tremendous portion of the experience. Let the caps break in the continue the rolling, Sometimes overlooked for reasons that aren't clear to me. There are certain tubes that work better with other tubes so the best middle may not be the best with different outside tubes. Play around with it. The worst i thought for me were EH 12bh7s across all three. good luck and enjoy

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Sat Mar 23, 2013 1:42 pm

    Thanks. Good points. I tried 2 RCA 5814A's on the outside and the GE 5815A in the center last night! My wife and I have t had that much fun enjoying music in a long time. It seemed like a perfect combo but I won't leave well enough alone. Gonna try some different ones today.

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Mon Mar 25, 2013 2:34 am

    Spent the weekend with the new 6ca7's and rolling different combos of 12au7's and 5814a's. I definately like the RCA cleartop in the middle. Right now I have 2 GE 5814 on either side with it. Tried the JJ's and they sound good too. Do most of you use the same tube in all three sockets?

    nerpissad

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    Re: New tube combos help on VTA70 mod

    Post by nerpissad on Tue Mar 26, 2013 6:50 am

    I just ordered a telefunken ECC82/12AU7 to become the center tube and two mullard CV4003's for the sides. apparantly, these mullard's are mil. spec.
    I decided that if I was going to experiment with tube rolling I should get decent tubes and see what the fuss is about Wink
    if all goes well, the tubes will arrive tomorrow. so I'll let you know what my findings are.


    Last edited by nerpissad on Tue Mar 26, 2013 6:52 am; edited 1 time in total (Reason for editing : typo)

    peterh

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    Re: New tube combos help on VTA70 mod

    Post by peterh on Tue Mar 26, 2013 7:03 am

    Bigron865 wrote:Ok great. I just put one of the RCA clear tops in the center and seemed to get a little more separation and warmer vocals but it could be in my head. I still have the old Sovteks el84 in the output. The EH6CA7's won't be here till Friday. Maybe those will help too. I'm missing that 6v6 sound I had with the Stromberg Carlson but the bass on this vta70 is much tighter. Looking for that upper sparkle.

    You say "el84" but that must be a typo. Do uou mean el-34 ?

    Bigron865

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    Re: New tube combos help on VTA70 mod

    Post by Bigron865 on Tue Mar 26, 2013 7:13 am

    Yeah 34. Sorry

    pjp3

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    Re: New tube combos help on VTA70 mod

    Post by pjp3 on Wed Mar 27, 2013 4:35 pm

    What is the difference in 12AT7 or 12AX7 tubes verses 12AU7? Can these be used in the front position?

    Bob Latino
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    Re: New tube combos help on VTA70 mod

    Post by Bob Latino on Wed Mar 27, 2013 4:45 pm

    The difference between those three tubes is the GAIN level (mu) of the tube. Relatively speaking

    A 12AX7 has a gain level of 100
    A 12AT7 has a gain level of 60
    A 12AU7 has a gain level of 20
    A 12BH7 is a little lower than a 12AU7 - maybe about 17 .. but may be used in most circuits that call for a 12AU7.

    Substituting a higher gain level tube than the circuit requires is not good and can lead to instability of that part of the circuit. You might be able to use a tube that has a lower gain level but then the circuit may not be operating as it should.

    IMHO - use the proper tube and try different manufacturers of that tube to make subtle changes in the sound of the amp.

    Bob

    tubes4hifi
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    Re: New tube combos help on VTA70 mod

    Post by tubes4hifi on Thu Mar 28, 2013 1:51 pm

    there is more than just a gain difference to the tubes, they have totally difference electrical characteristics, which is why none should be substituted for any of the others, without making appropriate changes to the plate and cathode resistors.
    Also the 12BH7 requires twice as much filament current.

    peterh

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    Re: New tube combos help on VTA70 mod

    Post by peterh on Fri Mar 29, 2013 6:15 am

    Bob Latino wrote:What Roy has said is quite true .. keep the two side tubes the same ...

    Tubes that I have tried in all three positions are > 12AU7, 12BH7, 5814, 5963, 6189 and the Mullard CV4003. All work well.

    Bob

    I just replaced the 5963 shipped with the kit with plain ecc82. And the conclusion is that
    "Thou should not use computer stuff in audio gear".

    Anyone wanting 3 5963 ?

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