Blackstar Series One Bias Advice Required.

Handsome_ChrisHandsome_Chris Frets: 3723
I need to change the power valves (4 x KT88) on my Blackstar Series One 200w.   I've never done this before, but I am an electronics technician.  I have biased transistor based amp circuits, quite a while ago, so I suspect the principles are the same but have their own peculiarities.

Thanks for any practical advice offered.
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  • meltedbuzzboxmeltedbuzzbox Frets: 7903
    Wow you have the 200w jobbie?

    I hear the volume on that thing is biblical. 
    The Bigsby was the first successful design of what is now called a whammy bar or tremolo arm, although vibrato is the technically correct term for the musical effect it produces. In standard usage, tremolo is a rapid fluctuation of the volume of a note, while vibrato is a fluctuation in pitch. The origin of this nonstandard usage of the term by electric guitarists is attributed to Leo Fender, who also used the term “vibrato” to refer to what is really a tremolo effect.
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  • impmannimpmann Frets: 7611
    Talk to Phil at Blackstar Service.

    Be careful there’s 700v flying about in there...
    Never Ever Bloody Anything Ever.

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  • MattBansheeMattBanshee Frets: 784
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  • ecc83ecc83 Frets: 868
    Hi Chris. I generally give a straight "howtododis" for B's amps but in this case , Impmann has it. The voltages inside a 200 are seriously lethal. Yes, you are an electronics tech but NOT a valve amp tech or you wouldn't be asking?  There are two other factors.
    1) I would have to look up the procedure since I cannot recall where you set the power control.
    2) There are some shit KT88s about. I had a set that lasted all of an hour (at 100W pink noise) No names but  a precious stone not diamond! Phil will know what to fit.  They are not cheap.

    If you are REALLY determined to do it, PM me. I am not putting this into the public domain.

    Dave.
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  • @ecc83 , cheers for the steer buddy.  I am quite happy to bow to experience and knowledge in this area.  I am quite happy to admit that I'm not a valve amp tech, which it probably more like electrical technician land due to the voltages involved.  I had to ask though before I started the whole have-a-goer thing with trying to set up the quiescent current, if that is a thing in valve amps.

    Thanks for the advice.
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  • ecc83ecc83 Frets: 868
    @ecc83 , cheers for the steer buddy.  I am quite happy to bow to experience and knowledge in this area.  I am quite happy to admit that I'm not a valve amp tech, which it probably more like electrical technician land due to the voltages involved.  I had to ask though before I started the whole have-a-goer thing with trying to set up the quiescent current, if that is a thing in valve amps.

    Thanks for the advice.
    Very welcome. So, what are you going to do?

    Dave.
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  • Handsome_ChrisHandsome_Chris Frets: 3723
    edited January 5
    I'll give Northampton a call on Monday.   If it was a JCM800 I'd feel a lot more comfortable about doing this; however,  I can't find many Blackstar schematics online, let only for my specific model.  Also this may not be the amp for me to cut my teeth on.

    I've read stuff in valve amp books which I understand, but I think in this case I'd prefer experience on my side.  Maybe building a few amps from kits would a great bit of personal development for me?

    Can valves suffer from thermal runaway?

    Also I live in North Oxfordshire, so it seems a bit of a shame not to take it back home for a bit of work.
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  • ecc83ecc83 Frets: 868
    Best way I think Chris. All the Series One chassis have the same bias access point but  you need to know where the bias pot is!

    The "problem" is not so much that you are likely to get a shock inside the 200 (didn't make it easy! ) so much as the likely outcome if you did,  Most of us old amp and telly techs have suffered a serious "jolt" in our time  and even from 300-450V but 700 volts really is pushing survivability even for a single event and there is more than an amp behind it and 220mfd of cap!

    They are also NOT the easiest head to put back in its case!

    Yes indeed valves can suffer thermal runaway. When you see red plating on vlaves that means they are close to the "tipping point". Valves, especially modern ones, have a tiny grid gurrent that opposes bias which has a positve temperature coeficient and in a fixed biased amp and can lead to destruction.  When you bias a FB amp it is good practice  to run the *its off it for 1/2 hr or so (into a load) then check the bias again.  If you are getting a kit can I suggest FB 6v6?

    BTW if you see PhIl ask him for a set of the right fuses. The anode HT is a sort of special, 1A FAST blow.

    Dave.
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  • I spoke to Phil this morning.  I'm off to visit tomorrow.
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  • impmannimpmann Frets: 7611
    edited January 7
    Good. :-)
    Never Ever Bloody Anything Ever.

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  • @ecc83 , @impmann and others concerned for my welfare, rest easy as my amp is in with Blackstar's finest.  

    @meltedbuzzbox , yes it's the 200w jobbie. :P 
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  • meltedbuzzboxmeltedbuzzbox Frets: 7903
    @ecc83 , @impmann and others concerned for my welfare, rest easy as my amp is in with Blackstar's finest.  

    @meltedbuzzbox , yes it's the 200w jobbie. :P 
    Me and @impmann know. We saw you yesterday ;-)


    The Bigsby was the first successful design of what is now called a whammy bar or tremolo arm, although vibrato is the technically correct term for the musical effect it produces. In standard usage, tremolo is a rapid fluctuation of the volume of a note, while vibrato is a fluctuation in pitch. The origin of this nonstandard usage of the term by electric guitarists is attributed to Leo Fender, who also used the term “vibrato” to refer to what is really a tremolo effect.
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  • Did you see me driving around Anglia Way, like a lost fool?   =) =) =)
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  • ecc83ecc83 Frets: 868
    Did you see me driving around Anglia Way, like a lost fool?   =) =) =)
    Ah. Did you not know they'ed moved?

    Dave.
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  • Handsome_ChrisHandsome_Chris Frets: 3723
    edited January 9
    No I did not and neither does the https://www.blackstaramps.com/uk/non-warranty-service-centres .

    Luckily I tried the other address, after a quick Google, and I was back on track.

    Next time, I'm bringing biscuits with me, if only because my amp was carried from the car to the workshop for me. Thanks guys.
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  • impmannimpmann Frets: 7611
    Biscuits are *always* appreciated.
    Never Ever Bloody Anything Ever.

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