Mike,
I have Krell amps but I don't use a tube preamp with them. You can remove the jumpers in the amp yourself. You don't need to send it to Krell or need a dealer. Just remove the top cover and you'll see 2 jumpers on a small PC board located near the input connectors. The jumpers are next to a couple of small yellow color capacitors. By removing the jumper, the capacitors becomes in series with the input and blocks dc from the tube preamp.
Rich
I have Krell amps but I don't use a tube preamp with them. You can remove the jumpers in the amp yourself. You don't need to send it to Krell or need a dealer. Just remove the top cover and you'll see 2 jumpers on a small PC board located near the input connectors. The jumpers are next to a couple of small yellow color capacitors. By removing the jumper, the capacitors becomes in series with the input and blocks dc from the tube preamp.
Rich