12AX7 Tube Question

[Dead_Bishop]

Perhaps this isn't the correct forum but I will throw this out there.

My son's Laney uses a 12AX7 preamp tube. We are thinking of experimenting and perhaps trying some of the other 12A tubes. Any thoughts or suggestions?

Thanks,

Paul

 

[antichef]

What are the rest of the tubes? BTW, in "normal" circuit, you generally can't cause any harm by trying other 12A*7 tubes for a minute or two.

If the amp is "single ended", in that it has only one power tube, then going with a weaker preamp tube (like 12AU7) may improve the sound and perceived headroom some by not flooding the power tube with too much signal. If it's got more than one power tube (push/pull?) then doing this will just make things less loud. That's about the only general observation I can make. Different tubes sound different, but the difference can be hidden by other dominating factors in the amp, or not. Bad tubes will be really noisy and maybe microphonic (subject to internal feedback that causes an ear-splitting screech pretty much when you turn the amp on) - but these don't damage anything - you just take them back out

 

[dementedchord]

the only 12a_7 that i would not try change is whats called the driver tube or sometimes called phase splitter... it's usually the small one next to the output tubes... most of the time it's a 12at7... it has less gain than 12ax7 and is used here for it's cleanlyness... also refered to as a function tube... the rest of the small ones are mostlikely 12ax7 you can try any of the other 12a_7 for any of them... the difference in sound could be pretty extreem as laney's are pretty high gain amps... if it has 2 channels try changing just one channel for a different feel...

 

[slowmotion]

Do it. I used to have a hybrid (a trace elliot supertramp) which really reacted to different BRANDs of tubes, not just types. Assuming you are talking about a hybrid amp?

I tried heaps of different 12ax7s in there and it really did change the character. Ruby Tubes, Groove tubes, Sovteks, JJs, mesas (and some other rebrands)... I think I liked the JJs the best as usual. At the end of the day it wasn't enough and went all tube. Each manufacturer makes them slightly different so you get different flavours... but remember lots of tubes are simply rebranded (like the aforementioned mesas which are just chinese tubes graded for their amps), so swapping an EH for a sovtek won't make a real difference (or much of a difference).

I guess it's down to what style or sound you're after, but cleaner types (like the 12at7 or 12au7) might not suit if he's after more crunch; but yeah as above it depends on the amp design as to how it will affect the entire sound.

If you're talking about an all tube amp; changing the FIRST preamp tube often makes the largest difference in my experience. Leave the phase split tube as a 12au7 or 12at7, you don't want to hot that up. Otherwise honestly a fresh set of power tubes and a bias helps far more than changing your preamp tubes, but again that's only for all tube amps.

Check out eurotubes.com for great tubes and a lot of good info and service. Bob grades the tubes according to your taste; so if you want it a bit hotter he can do it; I've bought lots of tubes from him and he's always great.

 

[Dead_Bishop]

I guess perhaps I should have stated that the amp in question is a 65W Laney Tube Fusion, single 12X tube in the preamp, rest is solid state, and my son tends to play the clean channel most, and will switch channels for more crunch or bite as he needs it.

Thanks for the replies.

P

 

[slowmotion]

I guess perhaps I should have stated that the amp in question is a 65W Laney Tube Fusion, single 12X tube in the preamp, rest is solid state, and my son tends to play the clean channel most, and will switch channels for more crunch or bite as he needs it.

Thanks for the replies.

P

Ah, in that case, try a bunch of tubes until you find what he likes. If he plays clean most, perhaps try a lower gain one which might give you some more apparent volume...

Oh yeah - depending on the layout internally, the tube might only be utilized for one channel too (ie only on the gainier channel), so maybe check that out.

 

[stevieb]

From Ampeg's J-20 User's Guide:
http://www.ampeg.com/pdf/J20_OM.PDF

And my thread: https://homerecording.com/bbs/showthread.php?t=271997

The tubes used in preamplifiers (12AX7, 12AU7, 12AT7, etc.) are smaller than the
power tubes. These tubes amplify the signal from your instrument and shape the sound. They are inherently microphonic (they can mechanically pick up and transmit external noises). Since these tubes are used in the critical first stages of a tube amplifier’s circuitry, it is very important to use high-quality, low noise/low microphonic tubes for this application. Although tubes of this quality may be difficult to find and typically cost more than “off-the-shelf” tubes, the improvement in performance is worth the investment.
Preamplifier tubes are also used to drive the power tubes. When used in this application, a 12AX7 will produce a more distorted tone than a 12AT7, which produces a clearer, sweeter sound. A 12AU7 is even cleaner and brighter than a 12AT7, giving more definition to the sound. (In some cases it is possible to change the sound by changing the type of preamp and/or driver tubes. When making any modification to your equipment, it is highly recommended that you consult with a qualified service center.)