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If you were a tube preamplifier manufacturer

We all know NOS tube prices are increasing and getting hard to be obtained day by day,there are several new production power tubes accepted fine performer such as Gold Lion Reissue KT88 and KT66,Shuguang KT88 SC, EH 6CA7,JJ KT77, etc.. among the audiophiles.
If you were a tube preamplifier manufacturer,which type and brand preamp tube you would choose from the new production tubes and why?,considering
its linearity,frequencies band from top to bottom, noise and microphonic clearness ,dynamic and rich midrange spectrum,etc.. ( I find some tubes are noisy or microphonic some has great top end but loose the bass region or just the opposite ...)
Is there any new production preamplifier tube being great performer like the new production power tubes mentioned above?
Thanks
ben

Showing 3 responses by atmasphere

atmasphere's avatar
atmasphere
12,099 posts
 
As a manufacturer, you have to consider the lifespan of the product itself. Any decently built amp or preamp is going to last at least 20 years. At the end of that time, where are you going to find the tubes? One thing is certain- if you built the initial design to only work with a certain NOS tube from the get go, you have saddled the customer with a curse. At the end of 20 years, how common is an NOS type going to be if it was only available NOS 20 years earlier??

Of course you cannot predict what conditions are going to exist in the tube market 20 years in advance! But its a good bet that a tube that is not in production now is going to be a lot harder to find in 20 years.

IMO it is unethical to design a tube product that only works with NOS tubes.
atmasphere's avatar
atmasphere
12,099 posts
 
Mrtennis, correct. I personally don't use the 12AX7 because you can't get much bandwidth (the 12AX7 trades off bandwidth for gain), which is essential to getting phase relationships right. So if I need high gain, I use the 12AT7; you can easily get bandwidth out to 200KHz with that tube.

To get day to day consistency, the key is regulation, not the tubes. Tubes generally degrade slowly- over months, not days (unless there is a gross manufacturing defect), but day-to-day issues are usually something else- often the AC power. Good regulation will take care of that.
atmasphere's avatar
atmasphere
12,099 posts
 
Hi Mr. Tennis, The 12AU7 does not have a lot of gain. If you are making a low output MC phono preamp, its not the best choice. I find the sound of 12AT7s to be better than that of the 12AX7 because you can get bandwidth, but we don't use negative feedback (phono EQ is passive) and that gets you a more relaxed presentation. With 12AX7s it is a lot more common to EQ the phono by using negative feedback. If running feedback on the 12AT7s I might be inclined to agree with you.

The bottom line is that while the tubes do have an influence, circuit design has an influence too and can often get around tube issues, although in the case of excess microphonics, there is not a lot you can do.
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