Switching 845 tubes - do they have to be matched precisely?

Discussion in 'Hi-Fi and General Audio' started by Dynamic Turtle, Mar 3, 2006.

  1. Dynamic Turtle

    Dynamic Turtle The Bydo Destroyer

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    Hi folks,

    I have some Ming-Da 845 monoblocks and want to switch the stock "wood & twine" Shuguang 845's that came with the amp with some of the new Full Music/Golden Dragon Premium 845's. Problem is, I don't know if this is a simple swap, as the GD 845's probably have different electrical characteristics to the Shuguangs.

    Does anyone have the MC845-C's? Would appreciate some guidance here.

    Rgds,
    DT

    Will also get round to rolling the 6SN7 & ECC83's at some point...
     
    Dynamic Turtle, Mar 3, 2006
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  2. Dynamic Turtle

    bottleneck talks a load of rubbish

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    it depends if your new amp biases automatically, or if it has fixed bias.

    You definately want to check this one!

    Fixed bias means your amp needs setting with a multimeter before you can change power tubes.


    What are your initial impressions of the amp?

    Cheers
    Chris
     
    bottleneck, Mar 3, 2006
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  3. Dynamic Turtle

    Dynamic Turtle The Bydo Destroyer

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    Not sure tbh bottleneck - I assume autobias requires some kind of control circuitry? If so - this is definitely fixed bias! No PCB's in this baby! I'll double check with the distributor though. There's no way I'm poking round this thing with a multimeter - that would be asking for trouble. Might have to get someone round to help in that regard.

    I'm reserving judgement on overall sound quality until I replace the stock chinese tubes (which as you can imagine, are hardly the last word) with something more worthy of the amp. It sounds very promising in its current form though; listening to the Living Stereo/Offenbach/Gaite Parisienne SACD last night was a religious experience.

    Rgds,
    DT
     
    Dynamic Turtle, Mar 6, 2006
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  4. Dynamic Turtle

    Anex Thermionic

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    Self bias doesn't require control circuitry- its done with a resistor between cathode and ground. Basically your creating a voltage drop with the resistor which gives the cathode a positive potential, so it is positive with respect to the grid (the thing you bias when you do it manually). Usually theres a cap involved too so the AC signal can still see ground. I'm afraid other than that i don't know any specifics about your amp
     
    Anex, Mar 6, 2006
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  5. Dynamic Turtle

    Dynamic Turtle The Bydo Destroyer

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    INteresing - thanks anex. Its just that most autobias boards I've seen are PCB based, hence my original thoughts...
     
    Dynamic Turtle, Mar 6, 2006
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  6. Dynamic Turtle

    Anex Thermionic

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    what amp was that in? I'd guess there may have been something else involved.
     
    Anex, Mar 6, 2006
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  7. Dynamic Turtle

    Dynamic Turtle The Bydo Destroyer

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    I've seen Prima Luna, Shanling and AudioValve amps with PCB autobias boards. An exercise in cost-saving perhaps?
     
    Dynamic Turtle, Mar 6, 2006
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  8. Dynamic Turtle

    Anex Thermionic

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    Primaluna use 'Adaptive Auto-Bias' where they monitor voltages etc. around the circuit and adjust on the fly. That requires control boards and what not, its far more complex than standard self-bias.
    AudioValve use 'smart bias' which I think is a similar arrangement.
    Not sure about Shanling though- I thought they were manual bias with pots?
     
    Anex, Mar 6, 2006
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  9. Dynamic Turtle

    Dynamic Turtle The Bydo Destroyer

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    OK

    Pretty sure the Shanbling spc-80 blocks are autobiasing.

    DT
     
    Dynamic Turtle, Mar 7, 2006
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