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Hi all,
I am a newbie to tube and have a question to ask : Do I need a match pair of 12AX7 for my tube preamp section or they don't have to be match as per the tube seller said the preamp tubes have a very small tolerance, they don't have to be match, it's just another cash scam.
Is it true ? I've bought (2) unmatch 12AX7 tubes but haven't installed into my tube integrated yet as I'm not sure if it would be OK.
Follow Ups:
Thanks all you guys for your valuable inputs.
I'll plug the tubes in and play.
Redrose.
They will work. So plugging them in will not fry your preamp, if that's what you mean. I have no technical background, so take my advice with a grain of salt. If tube matching makes a difference, I would assume the following of importance/impact (from biggest to smallest):
1/ the biggest difference will come from ensuring the tubes have the same internal structure;
2/ comes from the same factory (identified in the production code);
2/ then measurement resutls;
3/ then production date. (from the same production batch would be ideal. But these days if the dates are fairly close, that's good enough.)You should also check with the manufacturer of the preamp to see how the circuit design uses the tubes. Each of these tubes has two sections inside.
1/ Some designs only use one section of each tube for each channel. So it would only be important to match that particular section of both tubes;
2/ Some use both sections of one tube for each channel, so it's important to match the two sections of one tube to the second tube;
3/ Some use one section of all the tubes for one channel, and another section of all the tubes for another channel. So it would be more important that two sections within each tube matches each other, and you could have tubes with different internal structure, different manufacturers plugged in at the same time.I guess the best way to find out is to play a mono recording with those two tubes in place to see if you hear any differences both in terms of volume and sound.
Another caution about measurement is that everyone uses different testers, and even if two people use the same type of tester, there are variances between two units, so you cannot just assume that two tubes you bought from two different places would be a matched pair just becaue the meeasurement resutls you have received from the sellers are close.
FWIW - I have owned a single ended tube preamp that used a pair of 12AX7 tubes and the designer recommended I use a matched set.
If you are operating a 'balanced' pre-amp. I understand some of those do need matched pairs.
Some pre's -- including the phono section in mine -- use one tube per channel. Its my understanding that it *is* better to get match pairs in that situation, though for non-techies like me you kind of have to trust whoever does the measuring to be honest and measure what actually matters. Correct?
I guess. You can err on the side of caution by using matched pairs, especially in a phono section, especially if you only have one tube per channel (I have 4). And if your manufacturer recommends matched pairs I assume they have a reason other than the psycological one of giving the impression that the pre sounds best with matched tubes to satisfy the more anal amoungst us. :-). I probably just have tin ears and couldn't hear a difference in my system with the units I'm using, both CDP's, pre amps, and amps. FWIW
Matching tubes can mean several things.
Assuming the tubes are of the same type 12AX7s not some other combination in a dual symetric circuit. Nothing bad will happen to a fixed bias amp or the tubes unless one is in bad shape and going to die anyway. The Match undoubtedly refers to the general emmissions strength as measured by common tube testers . They are inadequate to truly "match" the parameters of the tube under real operating conditions. If one tube has a poor ability to amplify a signal while the other is very strong you may be able to hear this difference in the final SPL of the two channels. That said both I and and A well known inmate have used "pairs" of tubes with large differences in the GMa or transconductance which is a slightly better measure of the emmisions strength. These pairs were measured with using more realistic testing conditions but still not true operating conditions. We both find the difference to be very slight when the spl of the two channels is measured.
I hope he chimes in here with the measurements but in any event it is small and it is very hard to discern this difference when listening.
The second scenerio is that the tubes are working in series or perform different functions, In my old SP6B preamp by ARC the 6 12AX7s are divided into a phono section and a line section. using mismatched tubes in these circuits is completely irrelevant. In fact I purposefully use different tubes in different positions to achieve the sound I want.
In sum one input/gain tube for a dual channel circuit may have a impact but IMHO it is usually small. In a series circuit as described totally irrelavant.
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