Lost one channel of sound in new VAC Sigma 160i's?

07-05-14: Philjolet
also, try swapping fuses, looking at them is not always enough

That is true, but checking them for continuity is much faster. I'd assume that tube amp owner should have at least simple DMM.
Checking bias from time to time can also signal about tube going bad.

also, try swapping fuses, looking at them is not always enough

Do the KT88's first, then the other tubes. You may be able to use the 6550's, but ask VAC first. To find out if you have bad tubes, just use the ones that are already in the amp.

We are talking about the KT88's right? Also, could a 6550 be used in place of the 88's until I can talk to VAC and get more of their tubes? I have some new 6550 that I use in my CAT amp. Thanks, Tra

"I think it must be a bad tube. How can I find that out?"

Just swap the tubes. Tubes on the left channel go to the right, and the ones on the right go to the left. I think there's a good chance that you power tubes are OK. On my VAC amp, I have 2 power tubes per channel. If you remove a tube, the amp still works. If your amp is made the same way, you would have to have 2 bad tubes; both on the same channel.

Thanks to all for suggestions. One side of sound is out no matter what component you select. Facing the amp, it's the left side or the right side if you were a person. I found the fuses and they look fine. I have tried different cables, checked all connections ect. I think it must be a bad tube. How can I find that out? I assume it's the large 88's.
Can't wait to get all corrected. Someone asked what the system is, Includes, Richard Gray power source, Cardas cables, VAC 160i, Esoteric K-03 CD, Sota Cosmos/V tonearm & Benz Glider cart. All plays to Khorns & DC10 Britton Ref speakers. Old school now, but Digital side is coming as I learn more. I hope everyone is enjoying a safe and Great Independence Day weekend. Again,Thanks to all for your help. Tra

Elizabeth is asking the right question. Have you lost sound in one channel regardless of which source you are using? Do you still get full sound in both channels using your TT?

In addition to rechecking your connections, you might try re-seating--or even swapping--tubes as well. You might have a dead tube.

This unit has just one fuse, right? I have a VAC 70/70, which has fuses for each side. When I lose sound in one channel, a blown fuse is usually the culprit, but I don't think that applies in your case.

Good luck with your troubleshooting!

What's the rest of your system?

swap interconnects just in case see if problem goes to different channel.
make sure you ID the component correctly.