Medium Duet tubes?

[pegleg32]

I just ordered a matched pair of Electro Harmonix 6L6EH tubes from Muscians Friend and I had to make a choice between: hard duet, medium duet, or soft duet. Completely stumped me, so I did a quick Google search and found a couple of incomplete references. I decided to just go to the middle and picked medium duet. Anyone have an understanding of these terms that can fill in some of the blanks for me?

[kbp810]

I assume they are referring to the expected bias point of the pair - soft being colder/lower mA and having earlier breakup, medium being middle of the road, and hard being hotter, higher mA and having a later breakup/headroom. Of course the way they word it is a little vague, soft and hard could just as easily mean the opposite of how I just described it.

[pegleg32]

Thanks Brian, one of the sources I googled said it had to do with the vacuum and that didn't make sense to be. Bias seems like a reasonable explanation. I'm a little surprised that they are sold like that. Must be a lot of variations in tubes.

[blackjack]

And even if they were referring to the amount of vacuum, a harder vacuum has higher headroom, and softer breaks up sooner. The US style tubes 6L6 etc, have a harder vacuum than EU style tubes like EL34 which starts to break up sooner/smoother. I hope they meant the bias point, because if they were going to give useful info, that would be first on the list.

[pegleg32]

do a search on Muscians Friend for Electro Harmonix 6l6 - if you were going to order a set, you would have to pick which "option" you want. That is where the hard medium soft shows up on the page. But there is no explanation of the options?