Dr. Z Delta 88 bias

Discussion in 'Amps and Cabs' started by myles111, Dec 6, 2005.


  1. myles111

    myles111 Member

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    I have done a bit of experimentation by changing the bias on the Delta 88. I looked at the data sheets for the KT88S, SC, and SV. These tubes are very strong, stronger than any 6550 as an example.

    These tubes are rated at 50 watts on the plates and 8 watts on Grid 2 (screen). The book design spec allows for 59 watts (this is not a typo) per tube in class A/B. On a Marshall Major we easily get over 120 watts per duet or 250 or so watts out of the quad in the amp.

    The plate voltage max is 800 and the screens are rated at 600 volts.

    In a typical Z Delta 88 with about 500 plate volts, 50% idle dissapation setting would be 50mA per tube, or almost two times what the amps may be set at from the factory. This would be general accepted spec for a KT88S, SC, or SV in this application.

    If you reset the bias to 50mA you will notice quite a bit more clean headroom and overall output. The amp will be a "different" amp in many regards and give any "100 watt Marshall type amp" a run for it's money to say the least. The Delta 88 will also perform better with any pedals than your typical cascade gain amp such as the Marshall, Mesa, Bogner, etc., to many folks ears.

    This amp is quite a monster when unleashed. I do not know if this may void any type of warranty so you may want to check with the good Doctor first (the tubes would be warrantied by the way if they are the stock GT tubes).

    The data sheet on the output tube used in the Delta 88 can be downloaded or viewed at:

    http://www.guitaramplifierblueprinting.com/Tube/KT88S.pdf
     
  2. The Whiz

    The Whiz Member

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    Not enough clean headroom!
    :mad:

    ;)
     
  3. myles111

    myles111 Member

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    The Delta 88 used to have less clean headroom than the KT-45 (which had as much or close to a Fender Twin ... while still being able to also do the Vox AC-50 tones and Hiwatt tones) with the factory Delta 88 bias. Now you will find it has even more clean headroom than a KT-45 and more than a Marshall 100 watter 1959 but also loves pedals even more due to the pentode front end and it also utilizes an ultra linear output section which is not the case on the KT-45. I measured well over 100 watts in these amps. They are more defined and articulate than the Marshall as there is not as much in the signal path ... only ONE preamp tube before you hit the phase inverter ... and not a lot of "pots" to pass signal through .... only bass and treble ... no presence or mid control and no cascading gain topology. Yet, if you want more front end gain just jack up the two tone controls and drop down the volume (sort of like a master volume amp).
     
  4. The Whiz

    The Whiz Member

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    I have a Z28. I know all about those cool ass tone controls. Always considering a bigger Z though.
     
  5. BIGGERSTAFF

    BIGGERSTAFF Member

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    The Delta 88 is a phenomenal amp!
     
  6. The Whiz

    The Whiz Member

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    Do you know of any clips of it anywhere?
     
  7. Laroosco!

    Laroosco! Member

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    +1000,000
     
  8. myles111

    myles111 Member

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    I know of no clips but Michael Burks has some CDs out that will show his style .... and from this link at Amazon there are usually clips.

    Not 88 clips but this is a guy that plays these ....

    http://www.michaelburks.com/music.html


    [​IMG]

    (don't be fooled by the KT-45 front panels .... this shot was before the Delta 88 panels were done and these were some of the first (if not the first) Delta 88s
     
  9. BIGGERSTAFF

    BIGGERSTAFF Member

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    Unfortunately I don't, and I don't have any clips of mine to post.
     
  10. Jim Fairbairn

    Jim Fairbairn Member

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    Roger,

    I know you've played alot of the Z stuff. How does the Delta 88 compare to the Route 66 from a tone perspective? I owned a Route 66, and although it had the "milkshake" tone, I wanted some more high end. Is the Delta 88 similar from that perspective?

    Jim
     
  11. BIGGERSTAFF

    BIGGERSTAFF Member

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    Jim, I haven't played the Rt 66 enough to say for sure. I can tell you that the Delta 88 has milkshake tone as well. I think a fair comparison tonewise would be-
    Rt 66 more in the JTM ballpark, whereas the 88 is more in the Major ballpark. There are no harsh tones to be found in the 88, but I wouldn't consider it an overly dark amp if that's what you're wanting to know.

    Rog
     
  12. myles111

    myles111 Member

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    Rog ....

    I agree with your JTM vs Major analogy.

    The 88 is not dark at all and in fact it was initially too bright for me in some ways. The tone controls are very effective so that is a blessing.
     
  13. Buckyboy

    Buckyboy Member

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    Do you mean that after a certain date the Delta 88 was revised to have more clean headroom than the KT45 or that rebiasing to 50mA gives it more clean headroom? If it was a cerain date do you know when the Delta 88 was revised to have more headroom or after what serial number?
     
  14. conundrum

    conundrum Member

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    If the Delta 88 is running so coldly biased from the factor, what is preventing the horrible crossover distortion I would imagine would be a result? Something to do with running it in Ultralinear?
     
  15. myles111

    myles111 Member

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    I find my KT-45 has more clean headroom than my Delta 88 even when the 88 is biased at 50% ID at 50mA
     
  16. myles111

    myles111 Member

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    Actually, there is xover distortion and when you run the bias higher you will find the amp less grainy.

    But .... at the factory settings the amp will sound crunchy and have a cool rock tone at lower levels.
     
  17. bluesmain

    bluesmain Member

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    I'm wanting to test drive both the 66 and 88. No Dr. Z's around our neck of the woods( Jackson, MS) though.The only dealer here does not stock them. Maybe someone would trade me for a used one ...say for a Victoria 35115.

    Johnny
     

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