Biasing Tubes vs Self Biased Amps.

[Brian27]

For the last 2 days or so i have been doing a little research on somethings and one of them was Biasing Tubes. I looked at 2 companies products. Peavey and Traynor. Some of the amps are Self Biasing and some arent. What are yalls opinions on the topic of biasing Tubes?

[Walker done done]

I've heard that it's good to bias each time you change tubes, but I've also heard if you're using the same tubes as before there's no need.  I don't know enough about it to say either way, but I do think that it's good to bias every so often (1-2 years).

[sour d]

I've heard that it's good to bias each time you change tubes, but I've also heard if you're using the same tubes as before there's no need.  I don't know enough about it to say either way, but I do think that it's good to bias every so often (1-2 years).

Walker you should definetly bias each time you change tubes. Some makers do say you don't need to if you use the same tubes as before but in my experience this is not true at all. I recently re-tubed a HRD with the same groove tubes and when I checked the bias they were running way colder than the set I had just replaced. Plus you can really change the personality of an amp by running your tubes a little hotter or colder. I can show you how to do it sometime if you don't already know how.
I guess a self biasing amp would offer the benefit of just slapping some tubes in and assuming they are running where you want them to be but I think being able to tweak your amp to your liking is what most of us are looking for. There are also amps that are "fixed bias" and these amps require you to change a resistor if you feel the bias isn't right. My musicmaster bass amp is like that. I know there are several videos on youtube that can show you how to safely bias your tube amp.
Here is a link to some info

http://www.justinholton.com/hotrod/bias.html

[Happyorange27]

Self biasing otherwise know as cathode biasing never need adjusted and have a more compressed sound.  Think Fender champ or some Vox amps.  On the other hand you have fixed bias which means the manufacturer fixed the bias to what they though was most suitable.  The wiring is obviously different and more complex.  It's getting it's bias off of a separate negative voltage area of the circuit.  However we all know that it's fun to optimize a bias so you can add a pot in the fixed bias circuit and that's how you turn fixed bias into adjustable bias.  Then you can experiment all day.
My BJ was fixed at 100% hot when I bought it so I installed a pot to make it adjustable.  Now it's down to like 70% and the tubes will last much longer.