rectifier tube swap question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by nik, Apr 2, 2004.


  1. nik

    nik Member

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    Would an amp need to be rebiased if the stock Sovtek 5AR4/GZ34 was replaced with a NOS Mullard or Amperex? or are the tubes interchangeable?

    thanks.
     
  2. redjet55

    redjet55 Member

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    the rectifier does not need any bias adjustment. But you’re also not likely to hear a great deal of difference between rectifier tubes.

    Longevity is the real advantage nos over new build, a nos tube would likely outlast the amp.
     
  3. nik

    nik Member

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    Thanks for the info. Yeah, I was just going to change it for reliablity reasons, but wasn't sure if different brand recitifers could change the amount of power to the power tubes where a rebias would be needed...
     
  4. redjet55

    redjet55 Member

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    not a different brand but a different type rectifier could alter the voltage. That’s getting beyond my knowledge...
     
  5. PaulC

    PaulC Member

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    There "shouldn't" be any problems changing rect tubes. But one problem that does show up is some venders are not really selling what they say they are. Some of the tubes today are not even close to what they were in the past. A year or so ago I went through a pile of sovtek 5Y3's for a champ in the shop. The B+ was about 40 volts over what it should have been - even when adjusting the line voltage for the correct primary voltages. Found a NOS 5Y3, and the voltages were dead on.

    Coming from the tech side of things I never do anything to the amps pwr supply/output stage without cracking it open and checking things... PaulC
     
  6. VaughnC

    VaughnC Supporting Member

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    Being that a rectifier can change the voltage in an amp, I think it's a good idea to check the bias when replacing one, especially if you have an expensive set of output tubes in the amp. It would be sad to see them go into meltdown if the amp happened to be under biased due to a voltage change.

    Every tube amp owner should own a bias meter, if for nothing else, to keep an eye on things. Personally, I run a pair of RCA 6L6 blackplates in my amp and they are nearly $200/pair, if you can even find them. So, I figure the $90 I spent on my Allesandro bias meter was well spent.
     
  7. KLB

    KLB Member

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    There was a batch of Sovtek 5AR4 a few years ago that were more like a 5Y3 equivalent.

    I got a great deal on a JTM-45 reissue that had one of these in it. The previous owner never got to hear the amp at it's best. When I measured the low plate voltage (around 355v), I new something was wrong. I put in a real 5AR4, rebiased, and the amp came to life, with plate volts around 410.

    - Ken
     
  8. nik

    nik Member

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    That's what I suspected...

    Thanks for the info guys.
     

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