Is it worth it putting a nice old tube in the PI spot?

CitizenCain

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4,819
I've got a couple of nice old Tungsol 12AX7s, not reissues. I've got one in V1 of my amp, V2 takes a 12AT7 and the PI is an older ('80s) Chinese/Fender 12AX7.

Would it be worthwhile slapping that Tungsol in the PI spot or better to keep it as a spare for V1?
 

scott1568

Member
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408
From what I have heard, the PI spot is not the main tone factor. A decent working tube will suffice. V1 on most amps (Fenders anyway) is the critical spot. I would put it away.

For example, I have 2 unidentified 12AX7's that came with my amp. Each one sounds better in V1 to my ear as compared to the new Tung Sol in there. So, I use the Tung Sol now, and put the old ones away for when I might play out or something.
 

doublee

Member
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4,432
Pardon but V1 is critical only to normal channel, no? Therefore V2 is most critical for the Vibrato (good) channel?
 

CitizenCain

Member
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4,819
That's what I've heard too, that the PI doesn't really contribute to the overall tone. Just wanted to check in at the think tank and see if I'm blowing smoke up my own skirt :D
 

guitarded_1

Member
Messages
1,349
Don't ever underestimate the ability for a PI tube to make a very noticeable difference. My secret weapon is a Mullard 4024 in the PI position on Marshall-type amps. It lowers the gain a bit, but it really makes the tone a lot more smooth and sweet.
 

PSaulino

Silver Supporting Member
Messages
1,377
The PI, I feel, is actually rather sensitive depending on your amp's volume design. I see big differences when I swap out tubes, but it is also the one that seems to benefit most from retaining whatever it is the manufacturer/builder puts in there. I wonder if it's because the amp builder tunes the amp to a certain set of new production tubes. The PI is the one slot where I seem to most often just leave it as is after tons of swapping. While every other slot has been swapped out for NOS.







I'm no amp tech, but.. From what i (think) I know..
It depends on the preamp /phase inverter design.

A Tweed amp, 4 input Marshall, and Princeton have some commonality in that the design such that the end result is that the audible clipping DOES come from the Phase inverter.

That being said, changing that tube can make a difference; the aforementioned CV4024 is one of my favorite tubes in that slot of a Marshall JTM, for instance.

Paul
 

Guinness Lad

Member
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15,853
With my experience of PI tubes I have found they can add to the overall brightness of the amp and some tubes will really make the amp sing. The funny thing about this is you might think the best tube you have will make the amp sing but sometimes it ends up being a cheap Sovtek. I really think how the amp responds is dependent on the output of the particular tube in question and what type of signal it receives in the first place.
 

Timbre Wolf

>thermionic<
Platinum Supporting Member
Messages
12,320
The PI position can make a huge tonal difference, depending on the amp. You can also change the feel of the amp by going to a different type (12AT7 for a 12AX7, for instance).

This is a really simple question to answer on your own - just try it.

By the way, the phase inverter is a fantastic place to use a coveted rare old tube that is microphonic in V1.

- Thom
 

Buddy Boy

Member
Messages
2,642
+1 for Mullard AT7's in PI. Just sent pmt for a pair from a TGP'er. None better in Fenders or Marshall.:BEER
 




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