any experience with audio valve?

I have unresolved issues with the AV auto bias system in the Challengers.
The lack of near by service facilities should be a consideration one should note before purchase.
The manufacturer will NOT provide you with a schematic so you can have them repaired by competent local vacuum tube specialists like Alan Kimmel or Tom Tutay on the East coast.
You have to ship these to the west coast and take a chance on real shipping damage. These beasts are large and heavy and are very difficult to ship safely.

I was offered the choice to remove my circuit boards myself and send them to Germany. Not an option for the technically uninformed.....

An update to my earlier posts of 2003.  Please review the history of the AV distributers or lack of distributers in the US.

My history is a disturbingly lack of manufacturer support of my AV Challengers to this date.  My Bias problem is unresolved to this day and one mono sits unrepaired while the other serves as an expensive sub amp.

The amps were misrepresented by the early retailer
and distributer in NY and AV company owners.  A long term disappointment.

The sound is good when they work but shipping these heavy amps to Germany or Canada for repair is no option.

If you search deep enough you will find a disturbing early history of problems with AV and their support.

I have quite a good collection emails from Helmut and Heike and others I have conversed with on their problems and repair issues they've had.

It's a shame the early problems weren't addressed appropriately as their products have such potential.  I believe the communication difficulties of the german designers coupled with poor follow up with their representing retailers and distributers damaged the brand somewhat in the US.

Do your research.

Toob, 

I don't understand ... you like the sound and it's been a boat anchor for years so why shipping to Canada for repair not an option?    After all, the amps were made in Germany and shipped to US? 

If you need to build a wooden crate is relatively inexpensive.  I was taught to use high density furniture foam for padding.

With years in this hobby, I find customer service is as important as SQ.   Everything eventually breaks so if can't get it repair, what good is it?

I would think that any decent tech would not need a schematic??