tube position question

Discussion in 'Amps and Cabs' started by tedisdead, Feb 18, 2009.


  1. tedisdead

    tedisdead Member

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    I've got a Crate VC20 that I just ordered new tubes for. I got two 12AT7's to replace the AX7's in position 1 and 2. So, how do I know which preamp tubes are postition 1 and 2? Are they labeled on the PCB? Is there a general rule for which is 1? IE: Left to right, or something. Any help is appreciated.

    Cheers,
    Ted
     
  2. plumcrazyfx

    plumcrazyfx Member

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    usually 1 & 2 will be the ones farthest from the power tubes.
     
  3. tedisdead

    tedisdead Member

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    That's what I thought. Just wanted to make sure. Thanks so much.
     
  4. nomadh

    nomadh Member

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    I've done things like that and didn't like it so much. Specially at7's. I like 5751 usually better. An at7 is supposed to be a good PI. Thats the last preamp tube nearest the power tubes. If you want to tame the gain maybe a single au7 in v1 or 2. I've been wanting to try a 12dw7 in my V30. Its half au7 half ax7. Good luck but 2 at7's in the pre is a radical change.
    Let us know how it effects the tone.
     
  5. tedisdead

    tedisdead Member

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    That's why I only got two. I'm also replacing both power tubes. I recently picked this little bad boy up, and it's noisy as hell right now. I figure I'll try out a few combinations and see which one works the best for me. Basically, I'm trying to get a good bedroom recording rig for my pedals. I like the sound now, but it's just so noisy. Hoping the new tubes help.
     
  6. tedisdead

    tedisdead Member

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    Sorry. Just noticed the "amp tech" forum. Sorry if this thread is in the wrong place. Mods, feel free to move.

    So, what exactly goes in which amp section? Any guidelines?

    Cheers.
     
  7. zombiwoof

    zombiwoof Supporting Member

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    That's right, you generally shouldn't use 12AT7's in gain positions, the tube is not designed for that. Use a 5751 there, instead, it has similar gain structure as the 12AT7. 12AT7's should be used for phase inverters and reverb drivers.

    Al
     
  8. tedisdead

    tedisdead Member

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    I wish I would have gone here first. The guy at thetubestore.com said the AT7's were a good idea, and also talked me out of EH power tubes.
    So, if I'm looking for a good clean tone at reasonable (apartment) bedroom levels, the AT7's aren't going to do it for me? I have a Marshall JCM900DR for louder stuff, so I'm not worried about loudness.

    Thanks again for all the help.
     
  9. tedisdead

    tedisdead Member

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    Well, I got them today and put them all in.
    It's definitly quieter now. No microphonics. Still sounds good, but different. I get quite a bit more gain before it breaks up now, and that give me a lot more tone to work with as far as the pedals go. I'm still relatively new to tube amps, having only owned two, but it sounds good to me. Very glassy and smooth using only the SD pickup booster.
    So, will the AT7's just not last as long, or is there something else? How is a tube affected by what it's "designed to do"? Pardon my ignorance with this, but I'm very interested.

    Thanks for the help so far.
     
  10. rockon1

    rockon1 Member

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    They will be fine. If it sounds good to you thats what counts. Generally I dont like AT7's in place of 12AX7's either-but thats just me. Too bright,thin. You usually dont get much gain reduction subbing a 12AT7 for a 12AX7 but you will get a different tone and in this case evudently less break up-which is what you were after. If your happy with the results thats the most important thing! Bob
     
  11. tedisdead

    tedisdead Member

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    After playing last night for a few hours, I'm starting to notice a bit of the thin-ness you're talking about. I'm going to put a 12AX7 back in P1 and see how that goes. Like I said, I'm still fairly new to the tube game. I guess ignorance is bliss at this point. Looking forward to becoming unsatisfied and broke.

    Cheers
     
  12. zombiwoof

    zombiwoof Supporting Member

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    Like I said, try 5751 instead of 12AT7 in the gain positions, it should do what you want. Keep the 12AT7's for phase inverter tubes.

    Al
     
  13. tedisdead

    tedisdead Member

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    The tube store said they would exchange them. That's cool. So, having only two preamp tubes, I don't have a phase inverter right? Pardon my ignorance on this one, but the help is greatly appreciated. Or, if you could point me to a thread that talks about preamp tube functions.
    Cheers.
     
  14. zombiwoof

    zombiwoof Supporting Member

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    I didn't realize that your amp only has two preamp tubes, but in that case V2 is probably the phase inverter. You can still use a 5751 there, if that is what you are getting, or a 12AX7, for that matter. If you haven't sent them back, keep one of those 12AT7's for the V2 position, and get the 5751 for V1. Does the Tubestore have 5751's? You really should get an NOS one for the best tone, there are not many new manufacture options for those. The GT 5751M is pretty good, but I know the Tubestore doesn't sell any GT products. I think there is a Sovtek/EH version, but I don't know how those sound. You could also leave the 12AX7 phase inverter and put an even lower gain 12AY7 in V1, or any combo of those tubes. The only new manufacture 12AY7 I think is the EH, I think an NOS tube would most likely sound better than those, but they would do the reduction in gain you're looking for. Sorry for the confusion, most amps these days have three preamp tubes, and I assumed yours did.

    Al
     
  15. rockon1

    rockon1 Member

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    Interesting. The schematic for the VC2112 shows 3 12AX7's. Checked some reviews on HC and one says it has 3 and another says it has 2? Redisgned along the way? Bob
     
  16. tedisdead

    tedisdead Member

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    tubestore has the sovtek 5751's. The problem is that neither position is labeled. I don't know which is V1 and V2. I still have the stock 12AX7's and I haven't sent back the 12AT7's, although I've pulled them out. Should I put one back in V2 with an AX7 in V1, or put two 5751's in? The AX7's are pretty noisy, so I'm thinking of using the 5751/AT7 option. Think that would work?
     
  17. tedisdead

    tedisdead Member

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    I have the 10" speaker version. There's an open position with no tube socket on the chasis, but I'm not there yet. haha
     
  18. rockon1

    rockon1 Member

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    The V1 is usually closest to the input jack. Bob
     
  19. tedisdead

    tedisdead Member

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    That would make sense. I've searched every seedy corner of the interweb for any shematics or labeling. Nothing. Not even Crate.

    I think I'm going to send back one 12AT7 and get a 5751. That way, I have one of each and can play around.
     
  20. zombiwoof

    zombiwoof Supporting Member

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    If you like the setup with the Sovtek 5751 and the AT7, keep your eyes peeled for a good NOS 5751, you can get them on Ebay for a good price if you keep looking. I'm sure the NOS will sound better than the Sovtek.

    Al
     

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