Using contact cleaner in tube sockets

 Do you have an ARC dealer within a reasonable distance? If so I would ask him to have a look and see what he thinks. If he is a nice guy, he will help you figuring his good will may earn him a customer in the future. He should be able to check the bias.It could possibly be a bad driver tube. But it could also be something else like a bad cap. 

 I would take any sellers claim of tube life or new tubes with a grain of salt. When I buy a piece I always assume it will need new tubes. If the tubes are bad or not closely matched and you send it to ARC for repair. The first thing they will do is replace all the tubes. ARC tubes are expensive and can really add to the price of a repair. That is why trying to see if an ARC dealer will help is the first thing I would try. Maybe even buy replacement 6922 tubes from a reputable dealer and ask the ARC dealer to install and bias them. Even if there is a small charge it would be cheaper then sending the unit back to ARC. I buy my tubes from Jim McShane. He burns his tubes in a bit before matching them just like ARC. 

 Good luck, I hope it is something simple that can be easily fixed.

Try cleaning the tube pins. Make sure the bottom of the tube (the glass) is clean as well. Use your cleaner and a Q-tip to scrub the tube pins. 

I have always wondered why ARC neglected to mention in the owner manual that came with the VT50, VT100, Vt100 mkll, and VT200 that when replacing the small driver and input signal tubes they would need to be biased. There is no mention of it at all. Nor is there any mention the difficulty of preforming the biasing of the small signal tubes. It’s nothing like biasing the power tubes. Biasing the power tubes is a cake walk compared to biasing, correctly biasing, the 6922 tubes. Especially the driver tubes.

I would not be surprised if the seller of the OP’s Vt100 knew the new 6922 he bought for the amp and shipped with the amp needed to be biased once installed in the amp.

The reason ARC tubes for the VT100 are so expensive is because each section of each 6922 must be tightly, closely, matched to adjust, set, the bias to within ARC specs. Many tube vendors do not spend the time to match their 6922 tubes that will meet the tightly close matching that is needed. The closer, the tighter, the 6922 tubes are matched the easier it will be to bias the tubes within specs. Even then it can be a PITA. Biasing the 6922 tubes is not for the novice. Lethal DC voltage is present at points the multimeter probes will be connected.



Owner manual. No mention when retubing the 6922 tubes they must be biased.
http://www.audioresearch.com/ContentsFiles/VT100II_Manual.pdf

Could also be a loose pin in the socket. I had that same problem in an Octave V70se and it was loose pins in one socket

For cleaning tube socket female contacts and male tube pins I use  isopropyl alcohol.