Pulling power tubes and bias...

[75lespaul]

Okay, so I'm going to get the Eurotubes pro bias adjuster thingy because I don't wanna fry myself. On my much talked about Bugera 333 combo, I've pulled the two middle power tubes to bring this down to 60 watts because one of the tubes came fried. Changed the ohms setting from sixteen to eight as you are supposed to do. So when biasing, does anything change with half power like that, or do you bias to the same settings whether two or four tubes? Also, if I get the quad, is the volume really going to be that much louder, or will the tone be better and worth the extra wattage? Thanks everyone.

 

[Surgeon]

Re: Pulling power tubes and bias...

IME the bias current will change as the current draw is less with two tubes vs. 4. With my 2204, I had to readjust when I pulled tubes since it started popping the breaker when I removed or added tubes without rebiasing. That being said, if you biased it very conservatively from the start, there MAY (keyword) not be a need to do it. However, since you have bought the proper equipment, I say just rebias accordingly. There's no "devide" or "multiply" in such a case, just bias each tube as you would normally if there were 4 tubes.

As for tone change with tubes pulled or not: having double the wattage will be approx 3db more, which isn't that much. You're going to notice a change in headroom mostly, which will have an impact on tone. What you prefer is strictly personal though.

Have fun!

 

[allbutromeo]

Re: Pulling power tubes and bias...

Good call on the Euro tubes bias probe/meter. It's one of the best investments I've ever made.

 

[Demanic]

Re: Pulling power tubes and bias...

Heebus! If you're going to buy the biasing meter, why not just spend the extra on at least a duo for the middle if not for a matched quad set. It's worth it. Then you can just set your output back to normal for the cab you're running and have much better, noticeable at least, headroom.

 

[75lespaul]

Re: Pulling power tubes and bias...

Heebus! If you're going to buy the biasing meter, why not just spend the extra on at least a duo for the middle if not for a matched quad set. It's worth it. Then you can just set your output back to normal for the cab you're running and have much better, noticeable at least, headroom.

Actually, that's what I'm going to do. I was going to get a duo, but decided to just spend the additional thirty eight bucks and get the quad. At worst, I'll only use two now and save the others as spares. Actually, the amp has great headroom now with half power. I'm really happy with it as is.

 

[Demanic]

Re: Pulling power tubes and bias...

^^
Excellent decision.

 

[75lespaul]

Re: Pulling power tubes and bias...

^^
Excellent decision.

Thank you sir :cool2:

 

[zzmoore]

Re: Pulling power tubes and bias...

You may not notice much "Volume" difference at all.
Impedance at the OT will not effect the way you bias your tubes, their spec for max dissipation will not change. If you are asking.....Should you check the bias after yanking two tubes, then Yes.
There is no answer to what You Will Think the improvement may or may not when switching from a pair to a quad.
good luck