Tube Biasing and Tube Specs

[diezelboy]

Hey guys

Quick question: how do you know if a tube has an earlier distortion level than other?
For the same brand of tube and make (Ruby EL34BSTR say) - matched pairs.

Say I plug in a pair of tubes (call it pair A) and I show 65ma bias reading
Then I plug in another pair of tubes (call it pair B) and I show 80ma with no change to the bias pot.

In order to bring pair B down to 65ma I have to adjust the pot accordingly

Which pair has the earlier distortion level?
Thanks

[Blue Strat]

In theory, the one with the lower mA rating. In practice, you probably won't hear the difference unless the readings are radically different.

[diezelboy]

So you're saying pair A is the one with the earlier dist. leve? I thought if a tube is sucking more current means it's early dist. I'm lost

[Blue Strat]

So you're saying pair A is the one with the earlier dist. leve? I thought if a tube is sucking more current means it's early dist. I'm lost

You said you'd be biasing them the same, right?

The one that draws the least current with the same bias setting has the least conductance. This tube won't be able to produce the same amount of clean power.

[diezelboy]

Yes, so the bias pot doesn't change. The proper reading for this amp must be 65ma per pair.
Pair A reads 65mA (so it's well biased and the pot is ajusted somewhere halfway) and pair B reads 80mA with no change in the pot.
To bring pair B to bias properly around 65mA I have turn the pot almost all the way.
Thanks

[diezelboy]

blue strat? ideas?