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Can tube output vary within a specific type?

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I've not dealt with tubes so I apologize if this has been frequently 'cussed before, but I just rolled in a pair of JJ ECC88's into my headphone amp, replacing some 6922's and I'd swear it's louder (I'll wait a while to make any other subjective pronouncements). But, it brought up some questions:

1) Is this just me?

2) Do tubes of a given type vary in output by manufacturer?

3) Or, is this just because the old pair was heavily used for a couple of years?

The last brings up another question: For signal tubes, i.e., preamps, etc, is it best to leave the unit turned on at all times, or is it better to turn it off when not in use?

Thanks in advance for any information.
It's likely that the older pair was just getting a lttle tired.You would probably see the difference on a good tube tester. It's possible that the JJ's have a little higher output when new and may settle down as they break in, if they're brand new. IMHO, regarding power on vs power off, I leave tube gear on if I'm going to be using it that day. I don't leave it on 24/7. It only takes an hour or so to get everything fully warmed up for best sound. Depending on the circuit and the operating class of the tubes, the cathodes just sit there burning away, even with no signal. If you know you're going to be listening, turn them on. Otherwise, conserve those firebottles. As for solid state, I would tend to leave this gear turned on more of the time. Thermal cycling (heating and cooling repeatedly) is a killer of this type of gear. If you get a chance to find some Amperex 7308 PQ's, grab 'em. Those are some of the best you'll find in that family of tubes.
Yes, Amperex 7308 and CCa!

Hello Lonestar,

agree with what John wrote.
JJ makes terrific ECC88 from what rumours i hear but to Amperex 7308 i would like to add as hint:
Telefunken E88CC
Siemens E88CC "Made in Western Germany"
Siemens CCa (type made for the German Mail office, said to be the best ECC88 sonically)

I have more CCa than i can use and would consider to sell some. But their market price should be high, 50US$ a piece or more.

Thanks for the offer on the tubes, but for now I think I'll just sit on things for a while.

While changing from the Phillips JAN 6922 to the JJ ECC88s did flesh out the midrange a small amount, the MuFi X-can V2 still offers NO advantage over the headphone out on my preamp (an ancient Acoustat TNP, JFet design, headphone amp is probably an opamp). I've run signal both through my preamp, and directly into the V2 itself, and the differences are marginal, if existant at all.

Could be that my ears are just not what they used to be and that really are great differences. Point is, if I make any further changes, it will be to dump the V2 and try to find something better. Mind you it's not bad, it's just that the HD600/V2 combo is not as great as all the S'pile hype made it out to be.

Besides, I need to put more funding into my darned TT.
FWIW, I've learned to avoid gear that uses that family of tubes. They seem to be rather solid statish regarding overall sound quality. I had an Audible Illusions (Delusions) 3a preamp and I just couldn't stand it after a while. You might want to think about upgrading your preamp with a decent tube type that has a headphone jack and dump your present headphone driver.
Just a note to say that there are small differences in transfer characteristics of ECC88 and 6922 types.

In general, the higher the transconductance of a tube, the larger the difference between tubes of the same manufacture but of differing production batches.

To my knowledge, it was Tim de Paravicini who popularised this tube in Audio in the late seventies or early eighties. Audio Research followed this lead and used it as a Cathode Follower in their SP6B preamp. I had SP6A then and did the modification. I never liked this upgrade. This is not a reflection of the tube's merit in audio applications. Tim's preamp did sound very nice. Perhaps, there is a lesson to be learnt here.

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