Amp Biasing

[iceman79]

I just put in new power tubes without having the amp biased. Is it crucial to have the amp biased by a tech before changing power tubes? The tube type is the same (EL84), I just wanted to try a different brand.

 

[TwilightOdyssey]

Re: Amp Biasing

Theoretically, yes, you should have the amp re-biased when you switch tubes. If you're only doing a compare/contrast, and they are the same type, you should be fine, but once you decide, have the amp biased by a professional.

 

[Edgecrusher]

Re: Amp Biasing

Actually most amps using EL84 tubes are cathode biased. General consensus is they dont need biasing when putting in new tubes as the circuit to an extent is self regulating. Sometimes you hear it referred to as "self biasing"... But that being said I still check the bias to make sure they arent too far out of spec. Sometimes they will run too hot and you need a larger value cathode resistor installed. This will just maximize the tube life.

 

[Scott_F]

Re: Amp Biasing

Just to let you know how far off some tubes can be from each other. I took out some JJ's and put in some TAD 6L6 tubes and they idle current went up to almost double!

So, biasing is hugely important.

Now what was said about EL84's it mostly true. I can't think of any EL84 amp I've owned that was not cathode (self) biased. What amp is it?

 

[Edgecrusher]

Re: Amp Biasing

Now what was said about EL84's it mostly true. I can't think of any EL84 amp I've owned that was not cathode (self) biased.

Was some of my info wrong? I only ask as I dont want to repeat bad info.

 

[iceman79]

Re: Amp Biasing

I changed the tubes in my Mesa/Boogie Studio .22+

 

[Quencho092]

Re: Amp Biasing

whats a decent biasing tool for DIY?

 

[Fiber-Optics]

Re: Amp Biasing

whats a decent biasing tool for DIY?

I think you should take it to a tech if you don't know exactly what you are doing. I have heard that a shock or something that the amp produces can be fatal.

 

[Quencho092]

Re: Amp Biasing

just want to get my hands on the tool so my cousin who's an electrical engineer could check it out and get my amp biased.

 

[Curly]

Re: Amp Biasing

I'd take a look at the Bias Rite over on Weber VSTs site. You'll probably want to ask Ted which version you need.

 

[aleclee]

Re: Amp Biasing

I'd take a look at the Bias Rite over on Weber VSTs site. You'll probably want to ask Ted which version you need.

+1 That's what I use.

 

[Curly]

Re: Amp Biasing

just a follow up note:
you want one that reads directly in milliamps, so you don't have to do any conversion

 

[mrid]

Re: Amp Biasing

whats a decent biasing tool for DIY?

I use this: http://www.srs-webstore.com/music/biastool.html

It's cheaper that Weber, and works perfectly.