#1
Hey guys, long time no speak!

Well its about time to re-tube my Jcm900 combo and I have no idea whether it needs re-biasing or not?!?!

Its the 100 watt High gain dual reverb 4102 2x12 model..........anyone have any ideas?

If not then I can just bang some new tubes in there.
Im thinking JJ's for the high gain stuff.

Also contemplating a gain boost mod on the circuit board, anyone done one of these and know if it sounds better?

Any help grately appreciated.

Tobz
Gibson SG (Heavily modded)
Fender USA Strat
Hohner 12 String-uber rare

Fender Silverface Twin

EHX Big Muff
Digitech badmonkey overdrive
Boss DS-1
Blackstar Distortion X
Dunlop Crybaby
Ibanez Delay
Digitech Whammy
#2
as long as they're the same type of tube as the ones you're replacing, no re-biasing is needed.

You will if you're changing tube types, however.
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#3
I think if you replace them with the same tubes you dont have to re-bias it .. however its probably a good idea to anyway .. but i could be wrong
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#4
You will need to re-bias your amp every time you change power tubes. Even if the tubes are of the same brand, line and make.

You could skip out on the re-biasing, as the adjustments you'll need to make are probably minimal, however if you want to maximise their sonic potential, you should re-bias.

If you are changing preamp tubes, you don't need to re-bias as the preamp section of all tube amps are Class A operation.
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Last edited by ragingkitty at Oct 13, 2009,
#5
The people who know how to bias their amp will tell you how important it is to do it.

The people who don't know how to bias their amp will tell you that it isn't necessary.
#6
now, i have never owned a tube amp (GASing for this http://www.straussamps.com/svt30.html ) so what exactly is biasing?
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#7
Quote by rocknroll93
now, i have never owned a tube amp (GASing for this http://www.straussamps.com/svt30.html ) so what exactly is biasing?


'ere you go...

http://tinyurl.com/yjmfc5u

that page has all the answers about biasing vacuum tubes. It's even got the answer to the meaning of life!
Quote by Blompcube
it's so cool to hate Gibson, even the federal Department of Justice hates them.

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( . .) This is Bunny. Copy and paste Bunny into your
C('')('') signature to help him gain world domination.
Last edited by ragingkitty at Oct 13, 2009,
#8
Thanks for the replies guys, gonna get some tubes and send it off for a bias in a few days time.

One thing is puzzling me though, is the 5881 tube the same thing as the 6L6?
Gibson SG (Heavily modded)
Fender USA Strat
Hohner 12 String-uber rare

Fender Silverface Twin

EHX Big Muff
Digitech badmonkey overdrive
Boss DS-1
Blackstar Distortion X
Dunlop Crybaby
Ibanez Delay
Digitech Whammy
#9
Just normal 6L6?

5881/6L6WGB are the same tube, if your amp needs or takes 6L6GC then DON'T use 5881 or 6L6WGB. They could melt down and damage your amp.
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Mesa Boogie Mini Rec 25
Mesa Boogie Rectifier 2x12 cab

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#10
always bias when you change your tubes even if they are the same kind
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