Slight Tube 'Whistle' - Help?

Hi. Two Questions on my preamp:

1. Someone asked me if the pre is "hard on tubes"...what does this mean?

The EH stock tubes became super-hissy after 800 hours...stock replacements on the way. Meanwhile, i put in Amperex 6922 US PQ White labels...better in every way. Silent...until just recently. After about 300 hours with the Amperexes, i now [occassionally] hear the teeniest, tiniest bit of "whistle" thru the R tweeter only. In general, the hiss is super, super quiet (and i have 95 db speakers)...but [sometimes not always] it has gone from effectively silent to a soft whisper now in both channels.

Can a preamp be 'hard on tubes'...and if so, is there anything one can do? Or is the 'teeny R-channel whistle' a symptom of this or something else...or just par for the course with any preamp...particularly one with a ridiculously low noise floor? i cannot get over how much super-soft detailing i can now hear thru ordinary recordings.

2. In trying to figure this out, with the unit on, i tapped each tube out of curiosity...and discovered i could loudly hear it thru each speaker. Is this normal? Should i care since i dont tap my tubes while i listen?

Other than the teeniest, tiniest bit of hiss and this occassional 'whistle', the unit is dead perhaps this 'tapping' business is a non-issue?? The tube sockets themselves are on their own floating suspension systems underneath in the unit apparently.

If i put an EAT tube damper on each tube, should this stop it? Again, should i care? this normal?

Thanks for any guidance!!!!!!!!!
First have you tried swapping the tubes to see if the sound moves to the other channel? Have you tried just re-seating the tubes?

Since the problem occurred after 300 hrs I personally would care. I can't see how a pre-amp would be hard on tubes. The pre section of my Octave has a single 12ax7 input feeding 2 12at7's or 12au7's. There are military versions of those tubes which are rated at 10,000 hrs. I have no experience with 6922's or tube dampers.
Yes, a circuit can be "hard on tubes" by running them toward the upper end of their designed voltage limits. Or, an off-kilter component elsewhere in the circuit can stress tubes. (I had a CJ tube preamp a few years back that developed a whistle when a power supply capacitor began failing.)

You didn't give the make/model of your preamp, but it might be worth calling the manufacturer and discussing the situation with them. You might want to have it checked.

And it is also not uncommon for tubes to be "microphonic" - some tube types are more sensitive than others. A tube damper can help if you think it is affecting the sound quality of your system.
Your hiss and whistle is commonly called "tube rush," and yes, they do that. Some more than others, some develop more or faster, and at least in my limited experience, preamps appear to be "better" at it that some other tube applications. Trick is to get some tubes in there that work for you, and have extra on hand -- because, sooner or later, the little bastards will start complaining again. And yes, the more sensitive and resolving your equipment, the more pronounced your perceived tube rush will be. When one channel starts to complain before the other -- that again makes perfect sense, as it would be unusual (though not impossible) for both channels to deteriorate at the exact same rate. Expect you should be able to find tubes with a longer shelf life, so to speak, but dealing with this stuff to one degree or another is just part of the care and feeding of tubes. Only permanent fix I am aware of is called "solid state."

As for the microphonics a ringing when you bang on stuff, also perfectly normal and -- as a general rule -- not such a great idea. Don't bang on them. If you've got a tube that is particularly sensitive to microphonics, such that the micro vibrations inherent in the normal operating environment are enough to result in a perceivable sonic degradation, then stuff like isolation or tube dampeners could help. But banging on stuff is orders of magnitude different, and not really helpful or representative. Think about a little kid poking himself in the eye and announcing "but mom, it hurts." Yes, then stop. Not obviously the same with tubes, but when you get right down to it, it pretty much is. Best of luck.
hah!!!! Thanks, Mezmo. Thanks everyone for your help. That was very reassuring. I will monitor...there is nothing but silence right now. some point may try the EAT tube dampers. i already use them in my DAC which is very, very to microphonic problems.

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If you have a whistle, that is a microphonic tube, and there is no operational parameter that can *cause* that, its just a bad tube.
Thanks, Atmasphere. i always enjoy learning from your posts. I took the tube out, tapped it lightly on the pins and re-seated the tube. It has been as quiet as in the beginning ever since.

A recommendation from Brent Jessee who has been great as long as i've done business with him.
Yes, some tubes seem to respond well to getting knocked about :)

I remember a few years ago we got in a batch of JJ 12AX7s for a guitar amp we make. They were all microphonic and unusable until they got thumped against a counter top. That seemed to sort them out...

I would regard something like that as a temporary solution, although in the case of those JJs, it seemed to be permanent!
Thank you for that...good advice as usual!

BTW, sometimes, when i have just turned on the entire system in the morning, it sounds like a vacuum cleaner is coming thru the speakers for about 5 seconds, and then it is perfectly quiet the rest of the day. If i mute preamp, during the 5 seconds, it is either tube DAC or preamp. But what specifically might that be?
oh...and the vacuum cleaner noise thru both speakers is almost as loud as a vacuum cleaner and does increase/decrease with volume control during the 5 seconds.

i will switch sources next time it happens to see if it is the tube DAC or the pre...but thought i would ask. AGain, after 5 seconds...dead silent the rest of the day. it is getting onto winter and it can be a bit cold in the room in the early am. thanks for any advice.
That sounds like a warm-up issue that can be associated with a tube or a regulator. It is not an indication of failure, more its sort of a curiosity.