[tonyptony]

Hi Frank. I decided to swap out the tubes in my 600R with a different pair of the exact same type - the only difference being that the tubes that were in there were running at about 90% on my B&K 707 tube tester. The replacements test out at about 105%. The way the sections balance out in each tube is about the same as the originals. Is this enough of a variation to worry about needing to rebias?

[avahifi]

You don't need to worry about rebiasing your 600R when replacing tubes of the same type.

Frank

[tonyptony]

Thanks Frank. Wasn't sure if the G_m differences would be a factor.

[martyo]

Hey Tony.
Are you still using those German tubes with the diamond on the bottom?
What were the biggest improvements when you upgraded your amp?

[tonyptony]

Why, yes I am.

Since I've been using these throughout the series of FetValve upgrades I have a fixed point around which I can compare the upgrades. My opinion of the last - the 600R - is simply that everything is better. More musical without being soft, more transparent without being dry or analytical, more dynamic without losing any ability to portray microdynamics. I think of the... what is it? - four different evolutions of my FetValve this one is one I can listen to and never think "hmm, is this little part or that as good as it could be?". Not that there was anything wrong with the earlier versions, but it's clear Frank and his team have been on a path to just make it better and better. Now I just sit there and listen.

If the AVA team were to figure out yet another way to upgrade this design, I'm honestly not sure I'd be willing to do it.