Bias question

[iknowjohnny]

safety factor aside, do you think it's better tonally to bias colder, say 50-60% if the amp is always played at loud levels?

[Andy Le Blanc]

Nope....

Most bias % are arbitrary and qualitative depending whom ever's opinion.

If you what it to sound like a crap fender go for it, see what I mean.


You need to know your signal in and get a I min and a I max out of
you amp and do the math to figure the harmonic content for your tube type and load.
Sucks like that. Every thing else is BS.

Do the math, I max and min can also tell you efficiency and where in AB land
your amp is in relative to load.

[Structo]

Take my D'lite for example.
It has a pair of RCA 6L6GC tubes in it.

The plate voltage hovers around 437-440v.

I set the idle bias at 36ma.

That's a bit on the cool side if you consider it a 30w tube.
But if you lower your max watts to 25 which I think is safer then it is closer to around 65% of a max of 70%.

I don't subtract the screen current from that.
So that is probably 4-5ma less than the current measured at the cathode.

But, if you run your volume high at gig volumes all the time, then setting it conservatively will probably make your power tubes last longer.

I haven't wanted to push these tubes too hard since I was very lucky to get these from a friend.
But he doesn't have a tube amps so he gave them to me.

Yesterday when I was messing around with it I had my meter plugged into the bias test points and turned the amp up to gig volume and slammed some power chords and the meter went up to 65ma.

Not sure how accurate that is but according to the Va x Ik it is around 56 watts.

[iknowjohnny]

Yesterday when I was messing around with it I had my meter plugged into the bias test points and turned the amp up to gig volume and slammed some power chords and the meter went up to 65ma.

Yeah, thats why i asked.I thought it would sound better at loud levels biased colder so that the bias would average a lower current. Mainly because if it goes close to or over 100% due to the amp being loud, don't you start to get odd order harmonics?

[dukeamps]

what do you bias your amps at? i bias mine 50watt at 33ma, that is with el34s

[iknowjohnny]

Thats about the same as me. I usually go about 37 without taking screens into account, so probably about the same as you. But of course it means little w/o plate V which is 475 for me and i assume thats the same for you since you are running the same PT right?

[selloutrr]

the bias as we have come to understand it.
The 70% rule is to give the best balance between tube life and volume. with that said bias is subjective to the designer and the player. in some amplifiers the circuit sounds better on the cold side i.e 60% in others it sounds better hotter 75-80% your upper limitation is tube life and red plating which will kill a tube in minutes. if you bias to cold the tone gets muddy and undefined.

so as a rule 70% is a safe solid place to start that works in most every circuit and gives the consumer the most for there invest in tubes.

[dukeamps]

Thats about the same as me. I usually go about 37 without taking screens into account, so probably about the same as you. But of course it means little w/o plate V which is 475 for me and i assume thats the same for you since you are running the same PT right?

see i live in germany and we have 230v at the wall, so i have been using the 240v tap, and i have 440. when i use the 220v tap i get 470, but i think 470 is to high for a 50watt? i thought the amp had more mids on the 240v tap