I have had a 3006 for about 25 years. I would characterize it as fast, hard hitting, slightly warm with extended highs and highly detailed and transparent mids. Very very smooth. BUT!, I did not recognize all these qualities till a full recap was complete. For some reason this Tandberg line, including the preamp are highly sensitive to quality electrolytics. Including and especially the large filter caps on the amplifier. For years my amp had a hum that I always assumed was due to a delaminating transformer. The transformer was humming, but it did not go away till I changed the filter caps. All other electrolytics had been changed prophylactically earlier. After the filter caps were changed the amp completely opened up. It is not quite a Levinson or Bryston in terms of the muscle and girth of the signal, but it is oh so musical and plenty fast, clear and fat. It is also beautifully transparent in the midrange. A superior amplifier all around.
It was a bitch changing out the big electrolytics. I had to disassemble the ground plate and ended up putting O lugs on all associated wires, pushed a bolt through an available hole in the chassis and and strung through each O lug in an ugly but perfectly workable cluster. There are no caps out there that will fit perfectly, but I found some that would work on Mouser or Digikey.
I realize that this is a very old thread, but someone out there may have a similar problem and I am posting this with the possibility that it may save someones amp. This amp is far superior to most available consumer amps from it's era and any contemporary amps I have heard for less than 2 to 3K (I have been listening to amps for many years. I was tutored in my repair skills by a local EE engineer who specializes in hifi in the Austin area.) Incidentally, I should add, that his opinion of this line is that the topologies are somewhat unique. The construction is robust, and the build is clever and artistic in an a nordic kind of way. Anyway, these amps are out there and they are a relative bargain.