Phase Inverter

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Dave B, Jul 14, 2004.


  1. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    Would replacing the 12AX7 phase inverter really make that much of a difference in my amp? If it does, is it something I would hear more, or feel more? Knowing the different gain factors for the 12A*7 series, which one(s) would you recomend trying first where I'd notice something? I think I have the gamut of low gain 12AU7's through a few different brands of high gain 12AX7's laying around, and even have a 12DW7 in the stash somewhere.

    I know someone will say to try them all, but I was wondering what some of you guys settled on and why? And what technically is going on here that the different gain levels have an effect on (in layman's terms, please)?
     
  2. Troy T. Blues

    Troy T. Blues Comstock Station

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    First of all, what is your amp and what (brand/type) are you using now?
     
  3. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    See my equipment line in my posts for my gear. I have a 12AX7 in there now, but don't remember which brand it is. I'll have to look at it and get back to you.

    Actually, the Dual Stage 30 has two phase inverters. One is for the 6L6 power amp section, and one is for the EL84 section. Maybe different preamp tubes do various things tonally with the different power tubes?
     
  4. Troy T. Blues

    Troy T. Blues Comstock Station

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    Duh...sorry Dave...I didn't notice that. Does the amp call for a 12AX7 in the PI?? I'm not too familair with that amp. I would like to know what brand it is as well.

    BTW, how do you like the Blue Collar?
     
  5. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    Just looked, and it has two JJ ECC83S tubes in the two phase inverter slots, which I put in there new last fall when I bought, and subsequently immediately retubed, the amp. It probably came with two Sovtek 12AX7A tubes originally, which were in my Twinmaster when I bought it new a few years back.

    I like the Blue Collar, especially with the presence control. It allows you to get sounds out of it that you can't with all the other 4558 chip driven overdrives that just have the single tone control. But I still haven't found anything like the Real Tube. It has more tightness to it than any other pedal I've tried. The Blue Collar sounds great on its own, but when I A/B it in a Boss Line Selector, it sounds looser. Guess it depends upon which flavor you like, eh? I like 'em both. Just depends on which sound I'm chasing at a particular moment.
     
  6. Dr Rico

    Dr Rico Member

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    I'm not familiar with the Dual Stage up close and personal like, but I've wanted to meet one. If if you want to trade it for something else to try, please let me know. I trade amps like a Bedouin...

    As for PIs, it depends on the amp, but in general you want a healthy PI tube to drive the back end. Some amps (like them of the wreckoid lineage) rely on the PI for some of the special sauce.

    I'd get a few and muck around and takes notes if I were you. But I'm like that...
     
  7. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    Well, Dr., I guess I'll go ahead and experiment. Sounds like you're saying I should keep the more powerful tubes lined up for the PI and ditch the weaker ones. And I'll take notes, because I'm like that, too, sometimes. Did it with a ton of preamp tubes in my Twinmaster a few years back. That helped me out a lot with picking them for the Dual Stage.

    But I'm sorry, Dr., I'm keeping the DS30 for now. Heard they only got about 50 or so out the door before Mesa Boogie stopped them.

    If you are really interested in learning about one of these, see the few reviews on Harmony Central. They are pretty good and cover all the bases. I would add that I'm enamored with the foot-switchable tube power amp sections (major tonal differences between the 6L6's and the EL84's), the foot-switchable speaker outs (I have my 6L6's going to the 2x10 open back top half of the cab for a very clean Fender-y sound, and the EL84's going to the 2x12 closed back bottom half for a more rugged Plexi sound), and the built in attenuator for the EL84's and the pseudo-master volume for the 6L6's (to allow you to balance out the volume levels coming out of your two sets of tubes).

    Sorry if I rambled, but there is a good bit of versatility in this thing. I won't say I'd never get rid of this, but if I do, it will not be in the near future. If I ever was interested in swapping, is there any other amp out there that may be similar to this other than a Road King or Blue Angel? I'm not that familiar with all the amps that you guys mention here on the forums.
     
  8. BritPaul

    BritPaul Guest

    I have a Dual stage 30 4x10 (SN 0009). Are you sure it has 2 PI's? Mine has only 3 preamp valves.

    I have tried various valve combinations and currently have Harma STR 12 AX 7 in V1 and V2 and a Military spec Mullard Ecc 83 in V3. I had Mullard throughout but found this made both Power sections sound to much alike. I tried a RCA 12Ax7,Mullard,Mullard set up-very vintage sounding.
    For power tubes I have RCA 6L6 GC and Mullard EL 84's,this gives one very Fendery stage and one Plexi. I also put some Brimar EL 84's in - very aggressive with edgy overdrive.

    I'm still running the sovtek rectifier but have a Raytheon to put in it.

    I cannot overstate how great this amp sounds and how versatile the 2 power sections are.
    Have fun trying out different valve cominations-the DS30 really does respond to tweaking.
     
  9. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    BritPaul,

    Thanks for the cool tube trial info. I'm looking forward to futzing around with my PI's a bit to see how they interact with each power amp section. I still use the 12AX7WB in V1. I haven't found anything as creamy when pushing the volume. I have RCA's for my 6L6's, and JJ's for the EL84's. Since they sound like a good bet, guess I'll be looking for some Mullards to try in the future. And I was thinking of trying a Copper Cap rectifier, as sometimes mine rattles a good bit (as it did on my Twinmaster).

    As an FYI, I found and bought a 1x12 combo version of this amp last fall, and then had Jeff Bober build me an empty head shell so I could use it more 'properly' with the Budda 1210 cabinet. When I went to his Budda shop in Baltimore to pick it up, I asked him about the preamp tube configuration in their amps. Here's what he said.

    For the DS30, the Normal input uses the first half of V1, and the High Gain input uses both the first and second half of V1 (same here for the Stringmaster, Twinmaster, and Verbmaster). V2 is the phase inverter for the 6L6's, and V3 is the phase inverter for the EL84's (or vice versa). All their other amps only have one phase inverter. If I remember correctly, the third tube (both halves) in the Verbmaster is for the reverb, and the third tube (both halves) in the Stringmaster is for the parallel effects loop, and since it has a level control, you can use it as a boost. I'd love to hear one of these, but I'm guessing they didn't make many more of these than the DS30's.

    Thanks again for your tube insights!
     
  10. BritPaul

    BritPaul Guest

    Cheers for the amp info !!!

    I'm going to try the RCA 7025 in V2

    I have an original Orange 4x12 that needs a bit of TLC- I'm going to hook that up to the Mullards.

    Its definately worth hunting down some decent EL 84's, I tried JJs first off but didn't like them. The Brimars sound unreal-my favourite set up is Russian pre's and Brimars. The Mullards are lovely and smooth,specially with a decent wah (I got a Budwah thrown in).

    Nice to find another DS owner.
    Keep in touch with your findings.

    Paul.
     
  11. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    Never heard of Brimars before. How aggressive and edgy? I don't want anything that's too nasty (though others might). I like the Plexi grind coming from the High Gain side through the EL84's, and would not want to sacrifice those dynamics for something a little to brittle.

    Where can I get them? Are they still made? NOS? Or do you just have to hunt for some used ones? I guess if they are easy enough to procure and don't cost me my first-born, I should get some to try out.

    BTW, how do your 4x10's sound? Is is open back, or semi-open? Have you ever hooked your chassis up to other configurations? I love using my 6L6's through the open back top half with the 2x10's. I can get lost in a trance and play through there for hours using my H2O and not switch to the EL84's or the closed 2x12's.

    I'm wondering how this 6L6 configuration stacks up against all the other great Fender circuit/amp clones everyone rants about here on the board. I can't say I've heard any of the other amps, not counting clips. Have you had a chance to hear Aikens, Carrs, Victorias, etc?
     
  12. BritPaul

    BritPaul Guest

    They're definately not brittle,they break up a bit earlier than the Mullards,in fact you can come off the attenuator one or 2 clicks,which is where I guess the extra attack comes from.


    They're NOS,made in East Germany by RFT,who went on to make Telefunken tubes btw,I sourced mine here in the UK for GBP 35 a matched quad.
    Watford Valves stock them for GPB 30 EACH!!! and have this to say about them "Good definition,high gain and when run hard distort evenly"
    I really liked them with the stock pre amp tubes.



    It's a semi-open cabinet. I've used a Marshall 4x12 with the Brimar EL 84 set up-could'nt stop playing "Communication Breakdown" : )
    I've got NOS RCA 6L6's in atm-they sound really big with a ZVexx SHO-Boogie like middly grind or back off the guitar and a classic Fender rythym sound.
    I use a '72 Strat with Frahlin pick ups btw.


    I've heard a few "Boutique" amps around the shows and I have to say that the DS is up there with the best,let alone the 2 power stages.
    I've been playing in a band recently where the bass player is a sound engineer-he swears it the best amp he's recorded.
     
  13. Dave B

    Dave B Exit... Dual Stage Left Silver Supporting Member

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    Are both halves of the preamp tube in the phase inverter used, or does it just use the first half or the second half?
     
  14. malabarmusic

    malabarmusic Member

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    Both halves, which is why some favor "balanced" triodes for phase inverters. I'm agnostic as to whether that's a good thing or not. Some say it's crucial, others say it's hooey. I don't have a clue. :)

    - DB
     

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