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Opinions on Balanced/Matched 12AX7 for PI


J.L.C.

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My favorite tubes these days for filling out everything but V1 and the PI is the Shuguang 8th and 9th gen chinese tubes. They're just a great sounding rugged tube. I've quit using anything New Sensor puts out. I had a couple of Tung Sol reissues {censored} the bed in less than a year so no more of those. You don't need the Mullard 12AT7 in the PI. Any nice Jan Phillips or similar NOS tube will work and they're typically $15 or so.


In my mesa DC-5 I run a 5751 in V1, a JJ in V2, Shuguangs in V3-V5, and a Jan Phillips 12AT7 in V6 (PI)


In my orange I'm running a similar mix...

 

 

I'm with madryan on what AT7 to get. I just got done A/B'ing a CV4024 and a Jan P AT7 and really couldn't hear $15 difference. You can get a Jan for $12 or $15 plus shipping and the Mullard is $30 + shipping. I have both though cause I gots to know for myself how they sound in my amps. Now you can save some money.

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There is no cathode follower in the mark series. Also, new sensor should be fine as cathode follower. Most 12ax7's handle at LEAST 500V across them. This is very unlikely in most tube amps, since the usual voltages range from 250V to 450V at the voltage source for preamp, and that is usually split by a high value resistor. So generally a tube will see about 200V across itself, and vary between 0V and the source voltage ex: 450V (rare)

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There is no cathode follower in the mark series. Also, new sensor should be fine as cathode follower. Most 12ax7's handle at LEAST 500V across them. This is very unlikely in most tube amps, since the usual voltages range from 250V to 450V at the voltage source for preamp, and that is usually split by a high value resistor. So generally a tube will see about 200V across itself, and vary between 0V and the source voltage ex: 450V (rare)

 

 

Thanks for chiming in diaz. I didn't know if the Mesa had a cathode follower or not.

 

I have read in places where guys were having the Tung Sols and Mullard RI's die as cathode followers. I hear they are right at their limits for handling the voltage there and there isn't room for error so to speak. I'm not sure what the numbers are. The LPS has a bad rep for not being able to operate as a cathode follower.

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There is no cathode follower in the mark series. Also, new sensor should be fine as cathode follower. Most 12ax7's handle at LEAST 500V across them. This is very unlikely in most tube amps, since the usual voltages range from 250V to 450V at the voltage source for preamp, and that is usually split by a high value resistor. So generally a tube will see about 200V across itself, and vary between 0V and the source voltage ex: 450V (rare)

 

 

I don't know man. I put a tungsol in my cathode follower (v3 on stiletto) died in like 10 minutes. I thought it was a bad tube so i ordered another, same thing. After that I talked to doug at doug's tube and he politley slapped me on the hand and said new sensor stuff was a no no in those stages. I looked around on different websites around and found the basically same information.

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Thanks for chiming in diaz. I didn't know if the Mesa had a cathode follower or not.


I have read in places where guys were having the Tung Sols and Mullard RI's die as cathode followers. I hear they are right at their limits for handling the voltage there and there isn't room for error so to speak. I'm not sure what the numbers are. The LPS has a bad rep for not being able to operate as a cathode follower.

 

 

this is what i understand from reading around on some different websites

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My amp tech says that if you run a 12AX7 in the PI where a 12AT7 is intended, usually all you will notice is that the power tubes are pushed a little bit more so you might get a slightly different distortion. "Balancing" the PI tube is basically snake oil. What are you balancing it to? The other preamp tubes working in a totally different function? Might as well balance your steering wheel to your car's tires.....

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  • 3 months later...
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So I finally ordered new tubes for the Mark IV:

 

V1 - Jan Philips 5751

V2 - Jan Philips 5751

V3 - 9th Gen Shuguang 12AX7-A

V4 - 9th Gen Shuguang 12AX7-A

V5 (PI) - Jan Philips 12AT7WC

 

Sounds awesome!!

 

I grabbed a couple extra Shuguangs so I can do some experimenting, but it sounds killer right now :)

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