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Differences between 12ax7's


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3/9/1997 7:04 PM
Ariel Pozzo
Differences between 12ax7's
I've got a couple of amps that use quite a lot of 12ax7 tubes in them (a marshall 6100LE and an Egnater MICA) and after tryin' some different brands (Brimar,Groove Tubes, Westinghouse and Mesa) I noticed, since the marshall uses seven of them and I don't have seven of each, that I have to decide how to mix them.  
The question is that those tubes sound Very different from each other (speaking of brands) and I'd like to know if someone out there has tried them and would give me some advice on the way they should be combined for the best possible tone (I think you should check the Marshall 6100LE schematic first).  
thanks
 
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3/10/1997 12:22 AM
Mike Tatro

Wow., an Egnater - lucky man.  
 
I have done a lot of swapping with various Chinese and Russian 12AX7s. Here's what I've observed:  
 
Chinese untested - brighter and thinner than Russians.  
 
Chinese MESA STR - about the same as untested Chinese. I'm not too impressed with MESA's testing.  
 
Chinese Groove Tube - IMHO, if you have to use Chinese, use these. Much broader and flatter freq response. I'm not generally a fan of Groove Tubes, but these are worth the extra money.  
 
Sovtek 12AX7WA - Plain vanilla Russian 12AX7. Smoother mids than Chinese and not nearly as bright. Moderate compression.  
 
Sovtek 12AX7AB - Premium Russian 12AX7. More compression, even sweeter mids, some hi freq roll-off.  
 
Sovtek 12AX&WT - Hi gain Russian 12AX7. I avoid these like the plague.  
 
 
Positioning-  
 
I've had good results mixing Groove Tube 12AX7s (chinese) with Sovtek 12AX7WAs and -WBs. I usually put the Groove Tube in the first position and use at least one Sovtek WB immediately after. The compression and sweet mids of the Sovtek WB warms up the Chinese Groove Tube. The brighter broader Groove Tube provides some much needed attitude for the Russion WB. I then use primarily Sovtek WAs in the rest of the imput path. Occasionally, I will use an NOS tube in the phase inverter slot. You just have to listen.  
 
mlt
 
3/12/1997 12:44 AM
John Martin

Could you go into detail on your feelings about the Sovtek 12AX7WXT?  
 
Thanks,  
JM  
 
3/12/1997 12:53 AM
Mike Tatro

I actually haver never used them. However, several amp techs I really trust  
despise them - too high gain. They feel that they lack finesse and detail.  
 
 
3/12/1997 12:29 PM
John Martin

I have some of the 12AX7WT tubes but have never tried them in any guitar amps yet. I AM an amp tech, but I always used the 12AX7WA and WB tubes. They sound good so why charge customers for a supposedly primo tube that doesn't add very much. I have also obtained some of the newer WXT+ tubes that are said to be like the old Telefunken 12AX7s. I have some of the old Telefunkens and they are excellent. So if the claims are right, they should be excellent for guitar amps as well as hi-fi amps, just like the originals. Will let you know.
 
3/12/1997 12:43 PM
Mike Tatro
Yeah, that's kind of how I felt - WAs and WBs work fine for me. These new tubes  
sound interesting. Will look forward to hearing from you.  
 
3/13/1997 12:19 AM
Tom
I personally do not like any of the Sovtek 12AX7s. They tend to have a very short life in applications where plate voltages are over 250 volts, such as the pre-CBS mod to Fender's pre-amp. They sound good out of the box, but after 40-50 hours they tend to develop alot of noise and microphonics. I admit these cases are somewhat isolated, but more-so than NOS USA tubes. If you shop the net, you can find good USA tubes for about twice what you'd pay for the select+ 12AX7s. I think the comparison to Telefunken smooth plates is mainly hype. How can a tube with 1/3 the plate size sound like and last as long as the Telefunken??? I would buy used and tested USA 12AX7s before I'd use Sovteks. If the circuit uses lower voltages, Sovteks are probably acceptable, if you are in a pinch.  
Tom
 

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