Tube Biasing

[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

 

[number 2]

i would assume the ones with the lower current rating because the ones that read 80 or 90 could take more current before clipping, if the tubes are rated for that much current.

If they are the same tubes, say they are EL34s and all four tubes want to see 35ma and you have one pair set for 35 a piece and another pair for 50 a piece, the ones with more current will distort, and also be worn out much faster.

 

[diezelboy]

OK, so in my case it would be pair B that has the earlier distortion levels, right?

Both pairs (all 4) are the same tube, same brand (Ruby EL34BST)

Thanks

 

[number 2]

if your running a pair at 80, your gunna burn them really really fast, unless its the sum of the two tubes, then your running them around 5ma hotter which isnt that bad, but will wear them faster.

If your running a pair of tubes at 80ma each, then its 160ma for the pair and they will die very very fast.

 

[diezelboy]

Hi
The reading is per pair like I said in my post (not per tube)
All I want to determine is which pair has the early distortion level.

Without adjusting the pot pair A reads 65ma and pair B reads 80ma.
I wanna know which pair (from my example) has the earlier distortion level?

I know that the right reading is 65ma, but that's not what I'm asking.
Thanks

PS. Using a Herbert.

 

[diezelboy]

ideas? anybody?