Mesa D-180 Preamp Tubes

Discussion in 'Amps and Cabs [BG]' started by sincity, Oct 27, 2003.

  1. sincity


    Oct 16, 2002
    My D-180 seems to breakup and distort (farting) too quickly these days. I opened it up (first time), and checked out the preamp tubes.

    I have 4 Sovtek 12AX7LPS tubes installed. Inside the chassis the preamp tubes sockets are labeled from left to right,

    12AX7 12AX7 12AT7 12AX7

    I do not know what the installed 12AX7LPS tubes are compared to the 12AX7. Also, will not having the 12AT7 installed in the third tube position be affecting the tone and overall output?

    All my tubes including the power tubes were recently installed by the previous owner.

    Also, I am not sure of name of the power tubes, but they have a diamond insignia with the number 23 in the middle and what looks like russian writing 6n3C-E on the other side of the tube.
  2. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    What you may have for power tubes is this one:


    Many U.K valve dealers sell this valve under all sorts of numbers such as 6L6GT, 6L6GB, 6L6GC and even one world wide dealer has Even branded it KT66.
    This valve does not like even moderate voltages therefore cannot be recommend under any circumstances

    In Russian, the letter pronounced "p" looks kinda like a Greek pi, which looks a little like an "n", and the letter that looks like "C" is pronounced "s". I've heard bad things about this tube elsewhere, so I'd bet that completely replacing the power tubes could make a big difference to that amp.

    For good currently available 6L6s at a good price, IMO it's hard to beat JJs (see, but to get some other ideas, check out the reviews at

    As for the preamp tubes, 12AX7LPS is just one of Sovtek's 12AX7s; there's no compatibility issue, but not all 12AX7s sound alike, so you could play with swapping in others if you like. But it seems to me that using a 12AX7 in place of a 12AT7 could well mess up your gain structure, so I'd definitely swap that one out for the right tube if I were you.
  3. sincity


    Oct 16, 2002

    Do you know what manuafacturer makes this tube?

    Thanks for the advice on the power and preamp tubes. I think I am going to order a Sovtek 12AT7 preamp tube to start and see if that makes a difference.

    I really like this amp and want to keep it, even though I just got a Mesa 400+.

    Thanks again.
  4. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    No, I don't know who makes that 6P3S tube; I just know that a lot of people seem to hate it! I can practically guarantee that that's NOT the tube that Mesa originally shipped it with.

    JJ supposedly makes a decent 12AT7 too; if you were thinking of checking out 6L6s from them, you might try their 12AT7 at the same time (no, I don't get a kickback from them;) ).
  5. You're refering to the original designation for the old Soviet tubes that Sovtek sells as the 5881. They're actually good tube and very reliable, but unless you put much more voltage on them than a 6L6 circuit uses, they don't sound very good. They're made in the Reflektor factory, in other words, the main Sovtek plant in Russia.

    If you're looking for a good set of tubes to go in the amp, JJ Electronics is about the best current manufacturer of 12AX7's and 6L6GC's. BTW, if you change the third tube from a 12AT7 to a 12AX7 you will lower its distortion threshold and increase its noise.
  6. sincity


    Oct 16, 2002
    I have read alot of other posts regarding the JJ's, and I am leaning towards putting them in my 400+, but I really don't want to sink a ton of money into the D-180 (bias control, etc.)at the moment.

    The attachment below is not the exact power tube in my amp, but the diamond marking is similar.

    Russian Sovtek
  7. sincity


    Oct 16, 2002
    Thanks again Psycho Bass Guy,

    I am getting bummed out (no offense) by your information. I really did not want to drop alot of cash into the amp. But, maybe it is the best thing to do. I am assuming as with the 400+, that I will need to install a bias control for the JJ's or any other 6L6 tube I install? Unless there is a drop in replacement for the D-180?

    What you said about the 12AX7 being used instead of the 12AT7 makes alot of sense.
  8. sincity


    Oct 16, 2002
    Well, I talked to Bob at Eurotubes, and he is sending me four JJ preamp tubes.

    3 ECC83 S 12AX7
    1 ECC81 12AT7

    Bob told me that using a 12AX7 in the 12AT7 socket actually increases the gain of the amp by 40% which is limiting my amount of clean headroom.

    Also, I decided to retube my Mesa 400+ with JJ tubes.

    So, I will see how the preamp tubes work on the D-180, and when I get the 6L6GC tubes for the 400+, I will throw 6 of them in the D-180 to see how the sound compared to the Sovtek tubes that are in there now.
  9. john b carvalho

    john b carvalho Supporting Member

    Oct 26, 2001

    I had just e-mailed Bob this past weekend about tube replacement for my D-180.And with his recommendation of the JJ tubes the total was 130.00 shipped,you can't beat that.

  10. sincity


    Oct 16, 2002
    The prices seem pretty good. To retube my Mesa 400+ was $217.00 plus $6.00 shipping by priority mail.

    Bob said the JJ tubes were straight drop ins on both amps. I told him about this forum and how many guys on this site recommend that a bias control be installed for non Mesa Boogie tubes.

    He did not think it was necessary. After talking with him for awhile, I was convinced. I know others will have a different opinion on this one, but for my purposes and I am willing to give it a shot and see what the results are without the bias control mod.
  11. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts

    Yes, yes, yes.

    When I bought my D-180 someone had done the same boneheaded thing and it behaved in a manner similar to what you described plus the master volume worked oddly as well.
    Get a 12AT7 and your problem is solved.
  12. sincity


    Oct 16, 2002