VTL 2.5 without stereo output

All of a sudden my preamp is providing mono output only. There is no mono switch or any other internal switches. I swapped the tubes (left to right) which didn't do anything. It sounds fine excep for the lack of stereo. Any ideas as to the possible cause? TIA

Maybe a dumb question on my part.

That VTL preamp has two pair of RCA outputs. Any chance you were swapping interconnects and accidentally plugged into both left channel or both right channel jacks?
Hi Albert,

I had the same thought. All connections are correct.
You have a puzzling situation, perhaps call VTL and ask for help. I'm not coming up with anything else.

Hopefully an Audiogon member with your same preamp will chime in.
I have a different issue, but similar in scope, whereby everything sound fine, and coming through in stereo. But, when you switch the balance left to right, the sound mutes in only one channel when turned left, and then when turned right still has music coming from both channels. When in the middle it seems to sound just fine.

Where mine is a loaner (although brand new) while I wait for a 5.5 I am not going to stress about it, but figured I have a 'balance' problem with a 2.5 as well.
Well, I feel stupid. I decided to disconnect everything and connect one source at a time. I had recently changed interconnects between the preamp and subwoofer. Doing it by feel I had plugged one side into the input on the sub and the other into the output on the sub. Once corrected, with both connected to the sub inputs, the problem was solved.
Wendell, at least it's fixed and that's good news.