Loss of Highs

Here is my problem. A few weeks ago I replaced a tube in my Aesthetix Rhea which seemed to causes some intermittent fluttering in the right channel. Turned out it was the right channel V1 12AX7. Anyways, I replaced both V1’s with Gold pin Electro Harmonix 12AX7’s. While I played some music with the new tubes, I noticed the fluttering was gone, but there was a bit more noise coming from one of the new tubes. I decided to put the old tubes in, and order another set of new tubes. Anyways, after I put the original tubes back, I noticed that my highs seemed to be diminished somewhat. The music sounded a little dull and some of the air seemed to vanish. I can’t figure out whats wrong!

When I play an LP vs. the CD version the same album, the LP still has more fullness to it, but the highs just seem flat compared to the CD version. Symbols with the CD seem to shimmer more and have more air to them than the LP. It use to be the other way around until I swapped the tubes out!

I have a Rega P5 with a Glider SL and have double checked the tracking force, anti-skate, and made sure the table was level! Everything is perfect! All of the tubes are seated correctly and the cartridge loading and gain are where they always have been! I even tried another pair of tubes and nothing changed! I just cant figure out what is wrong! Any ideas?

The original tubes did not sound bad, I just noticed an intermittent fluttering noise coming from the right channel that prompted me to change the tube.

Any ideas of what may be wrong, or recommendations would be appreciated!

Thank you for your help!
How old is the Rhea? How old are the tubes in the Rhea? You don't provide this info in the OP. You may need to replace the whole set (10 tubes?), making sure to order Low Noise (LN) tubes where applicable. It sounds as if the EH 12AX7's that you put in were NOT LN 12AX7's. LN 12AX7's are specifically designed for phono stage applications and usually cost a bit more. Regular 12AX7's, the kind meant for a line stage, will usually cost less and have a higher noise floor.

Once all tubes have been replaced (assuming they are not all new to begin with) hopefully your problems will disappear. Make sure to clean all sockets before inserting new tubes. Good luck.

Looking for low noise 12AX7?
How about CV 4004 by Mullard, military grade, very low noise, long life, easy to find matched pairs and excellent for tube phono.

More important, still reasonably priced when comparing to Siemens or Telefunken E83CC.

Good luck
Thank you for the responses! Unfortunately, I do not know that age of the tubes. I purchased the unit from an authorized dealer as a demo unit. I would imagine the tubes are at least two to three years old. I just don't understand why changing the tubes, and then putting the old tubes back in would effect the sound at all! Any ideas? How do you clean the sockets? Are loss of high frequencies a symptom of aging tubes?

Thanks again for your help!
I'm laughing: You probably didn't realize the highs were diminished with the older tubes until you compared them to the new ones. The old ones are most likely beat.

The new tubes may have an issue? Where did you get them? You might need a 3rd set of tubes?
When you plugged the unit back in, did you have to reset the gain and loading to the proper values, or were they already at the proper values? I wonder if they are displaying the old info, but not operating with those values? Try adjusting the gain and loading away from, and back to, the values you want. You never know.

Also, it may take some time for the circuits to warm up after the unit has been turned off (I'm assuming you leave the unit in stand-by when not using it).

One final thought. Can you associate the diminished highs with a particular channel? Maybe use the balance control and see if you've lost the highs on one of the two channels. If you've lost them on both, that would be a good sign that it's not the fault of the tubes.

Oh, and double check your interconnects.

Oh, and make sure you've not inverted phase.

Oh, and maybe email Jim White for tube recommendations. Aesthetix products have a reputation for being finicky with tube choice.