Output level inexplicably reduced- help


I have an Volume output level problem with my system. My electronics are Audio Research:
Reference 150 amp
Reference 3 preamp
Reference 2 phono preamp

Lyra Atlas cartridge

This system was running great for three years. Nothing has changed. Now, my highest output level is inexplicably reduced. I cannot get a volume level greater that about 90db. I just re-tubed my amplifier and expected that to solve my output level problem, but it didn't happen.

I have always run the pre-phono on low gain, load 50k. The sound was warm, detailed, great soundstage - everything was great.

Now, the only way I can higher output volume is to switch to high gain on the pre phono, keeping the load at 50, or 100k, it doesn't seem to matter much. I can get the big volume, but, the sound loses its smoothness and warmth. It has an edge if I switch to high gain.

Can anyone provide me advice? I would surely appreciate it.

Thanks

PS I'm not losing my hearing.
128x128shaq
For starters, do you have a CDP, DVD, or blu-ray player you could hook up to the Reference 3 preamp? If so I would start there. If you have plenty of volume output playing a CD then that will rule out everything downstream of the line level inputs of the preamp.
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It is more likely either the Ref 3 or Ref Phono 2. Do you have another source you can try? Even a cheap DVD player so that you can see if the Ref 3 is working properly. It sounds like it is a problem with one of the tubes. Are all the tubes in both preamps lit? How old are the tubes in the Ref 3 and phono 2, especially the 6550 in the power supply? It could be a very week power supply tube in one of them.
It may be the famous ARC "blown resister". I traded in my ARC Classic 60 (for a VT-100) and the proprietor informed me that I had a "blown resister" on one of the tubes
(I had no idea there was a problem).

Now when there are 3 good tubes, the volume drop may not stand out (on a given channel). But in a power supply role, it may make a big difference.

Also, have you switched IC's lately? Going from RCA to XLR?
If so, there will be a drop in volume (at your regular volume setting).