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Guitars, Gear, Tone!
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 Post subject: Vh4 bias issue
PostPosted: Wed, Apr 19, 2017 6:48pm 
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Plank Cranker Trainee

Joined: Sat, Oct 02, 2010 6:42pm
Posts: 585
Hi all! I have a 2002 vh4 and a newer I think 2013 vh4. I was biasing both of them and using my DMM at the output transformer. on the 2002 vh4 going between the red and blue and the red and yellow. with the 2002 with a matched quartet of JJ KT77, I would set the bias on 70 using the red and blue. I would then check the red and yellow which would be very close.

with my 2013, when I bias similarly from red and blue, then switch to the red and yellow to confirm close value, it's 15-20 mA off. I tested it with 3 sets of KT77 matched quartets and the same thing happened all 3 times.

Questions:
is there something I'm doing wrong?
is there something beyond my power here that requires a full amp tech check?
is it dangerous to have that difference between the two sets of wires (it sounds killer regardless:-)

thanks!


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 Post subject: Re: Vh4 bias issue
PostPosted: Sat, Apr 22, 2017 8:17am 
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Plank Cranker Trainee

Joined: Sat, Oct 02, 2010 6:42pm
Posts: 585
Anyone?


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 Post subject: Re: Vh4 bias issue
PostPosted: Sun, Apr 23, 2017 2:50am 
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Diezel Amplification
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Joined: Sun, Jul 02, 2006 5:43am
Posts: 4688
Please check the 1k screen resistors.


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 Post subject: Re: Vh4 bias issue
PostPosted: Sun, Apr 23, 2017 7:42am 
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Plank Cranker Trainee

Joined: Sat, Oct 02, 2010 6:42pm
Posts: 585
Thanks! I assume that's an issue I should take to the amp tech...will he need schematics or anything like that? Thx!


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