Phase inverter peramp tube question

Discussion in 'Amps & Cabs' started by Tazz3, Apr 2, 2016.

  1. Tazz3

    Tazz3 Active Member

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    my new bugera 22 has a phase inverter peramp tube along with 2 other
    Permap tubes ,i read that u could use any preamp tube in the phase inveteer
    Slot is this true?? Cause this place said u can just a question im not upgradeing yet lol

    http://www.eurotubes.com/store/pc/viewPrd.asp?idproduct=1508
     
  2. peejaybee

    peejaybee Well-Known Member

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  3. 67plexi

    67plexi Well-Known Member

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    The phase inverter tube to me is the most critical tube in the signal chain that would be V-3 that connects the pre amp to the power amp.
    I put a high reading NOS 10,000 hour tube in the PI it takes the most abuse. When I get a amp on my bench no sound 50% of the time it's a bad
    PI tube.
     
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  4. syscokid

    syscokid Well-Known Member

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    It's widely accepted that the preamp tube for the Phase Inverter should have matching or balanced triodes.
    What Eurotubes is stating is that because of the design of the Bugera 22, which has a Short-Tail phase inverter, a balanced PI tube is not necessary. So as long as the tube tests good, any 12AX7 or ECC83 should be fine.
    Hell... you can even use a preamp tube with a less gain-factor, like a 5751, 12AT7, 12AY7, or 12AU7 in there. But this is another can-of-worms that should be left to more knowledgeable amp geeks!
     
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  5. frankd

    frankd Well-Known Member

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    One thing for sure Tazz most amps new unless they are custom builds don't usauly
    come with good tubes and some decent tubes and a change can make a lot of difference in the
    amp it seems your off to a good start with your new tube amp asking good questions and preparing to
    CHANGE THOSE TUBES also be careful very careful!
     
  6. ivan H

    ivan H Well-Known Member

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    Hi, the V22 uses a concertina style phase inverter where one 1/2 of the output stage is fed from the anode of one triode, while the other 1/2 of the output stage is fed from the cathode of the same triode, so balanced triodes aren't necessary, however you do want a quality tube there if possible as this type of phase inverter can produce some ugly distortion artifacts if driven too hard. Hope this helps. Cheers
     
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  7. syscokid

    syscokid Well-Known Member

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    Yeah... What He said... :yesway:
     
  8. Tazz3

    Tazz3 Active Member

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    Thanks when i do the upgrade i will get 3 matched pair of the tun sol thanks
     
  9. ivan H

    ivan H Well-Known Member

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    Hi, if you are using new production tung sol's, I would probably use an ECC803S gold pin for the phase inverter (tested of course). Just my opinion. Cheers.
     
  10. ScottMarlowe

    ScottMarlowe Well-Known Member

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    Note that the PI part of the tube is normally running at unity voltage gain and is generally used to provide more current to drive the power tubes. For this reason tubes like 5751, 12AT7s etc are often a better choice as they are usually capable of delivering more current (esp 12AT7s). On a lot of amps that use 1/2 the PI tube for voltage gain and half for current gain/PI (Peavey Classic series for example) it's a balancing act of tone in the voltage gain section and current in the PI section.

    Right now all my amps use Sovtek 12AX7LPS (very neutral sounding) for PI but I've got a few other tubes to play with. However really testing out a PI involves cranking up the amp, something my apartment dwelling neighbors aren't fond of.
     
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  11. ivan H

    ivan H Well-Known Member

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    The triode of concertina type phase inverter's that do the actual phase splitting usually produce a little less than unity gain so the preceeding triode is used to boost the signal from the pre amp a little, to make up for the loss in the phase splitter. Another thing with these phase inverters is the cathode is sitting at kinda high DC potenial. Many new production tubes don't have great heater to cathode specs so its an idea to put one of the better spec'd tubes in this respect in there. Cheers
     
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  12. jtcnj

    jtcnj Well-Known Member

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    Maybe I misunderstood but you dont need to match preamp tubes, just power tubes. the two separate channels probably each use 1 preamp tube before and after the vol / tone pots, then both go through the PI, possibly using the first triode as a make up stage after the tone stack and the second as the cathodyne PI. I dont know that circuit, but the point is the power tubes are run in parallel off the PI.


    You CAN run different 9 pin tubes (but not EL84s) in the preamp stages, (the gain factors are different), BUT the circuit (plate voltages, bias resistors, etc.)
    is designed around the tube type it came with. They are not Equally interchangeable.


    http://www.thetubestore.com/Resources/Guitar-Amp-Info/Gain-Factor

    Dont overthink this just play it man, play it.
     
  13. ivan H

    ivan H Well-Known Member

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    Yes, that is right, you don't need balanced triodes in the pre amp, or concertina type phase inverters. Long tail pair type phase inverters on the other hand I personally think its preferable to have balanced triodes, but then, I also "tune" the plate load resistors here to get a specific DC voltage difference between the two plates so maybe I'm a bit fanatical. Cheers
     
  14. syscokid

    syscokid Well-Known Member

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    Most of us here, are too... :cheers:
     
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