Mini Jubilee 2525H preamp tube questions

[Dave J]

So I have a Sovtek 12AX7-LPS that I picked up from somewhere a while ago ( might have been from Amazon?) and decided to put it in my PI slot of my Mini Jubilee. I have read that a Long Plate 12ax7 can be a good thing in that slot. My amp has the originial Marshall branded ecc83's in it now. It didn't sound better, maybe worse. Did some reading and learned that for the PI slot it's best to have a balanced preamp tube. I don't have the ability to test tubes for that so I assume the Sovtek is either just not a good one, is not balanced well or both.
Does Marshall aim to put a balanced tube in the PI slot? Or is it just whatever is next up in the bin, untested by anyone? These are the Studio series that are made in the UK so if in fact having a balanced tube in the PI slot is desirable, I'd hope they make that effort for the higher priced, UK made Studio Series.
I have a modest collection of 12AX7's, some old RCA and GE's given to me by a friend who was cleaning out his basement, as well as some 1990's Mesa branded 12AX7s ( one a SPAX7) that I can try in the amp. With no test equipment I can only go by how it sounds. The nice thing about the head is that it's easy to swap them. Also thinking about just getting a known balanced tube from a tube dealer so I know what I have. I can always try the other tubes in V1 and V2.

 

[maico996]

V1 is typically where you'll notice tonal/gain differences. If you're gonna roll some tubes through your amp, that's where I'd try first.

 

[Jethro Rocker]

Balanced isn't that big a deal on a PI. Especially audibly. I am surprised you hear a difference.
V1 is, as mentioned, by far the biggest change you can make and at that it will be subtle. Try an old RCA or GE for fun, really great old tubes.
As far as I am concerned you can use basically anything in V2.
Remember the LEDs come after the V1 tube in lead channel so anything further down the chain does not affect it much.
The SPAX7 has been tested and found to be of less noise than most others. Mesa doesn't make their own.
Is a good V1 tube in a high gain amp.

 

[RLW59]

A big, messy, can of worms.

When you look at a schematic you see very exact resistance and capacitance values. But in real life all those components have tolerances -- often plus or minus 20% of the rated value. A plus 20% resistor in one amp is 40% different than a minus 20% in another amp. (The more critical values are usually tighter tolerances, but even small tolerances can add together to make big differences.)

So in three different 2525's, one may be closer to the designer's intention with a PI that's stronger on the right side, the other with a PI stronger on the left side, and third with a balanced PI.

Then there's personal taste. Something that's not exactly what the designer intended might sound better to you.
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Plus there are other factors besides balance. A tube that's strong on both sides sounds different than a tube that's weaker on both sides, even if they both have the same balance.
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You can't hurt anything by using an unbalanced tube in the PI (or any other position). So the best thing to do is try the various combinations.

More can of worms -- you might not like the Sovtek as the PI with the stock V1 and V2. But it's possible it could end up your favorite PI with different tubes in V1 and V2.

 

[Mad Jack]

In my opinion, It’s not necessary to use a balanced tube in the phase inverter.
I have already use a 12at7 in phase inverter! Sound cool! You can try it. 👍

 

[RLW59]

Balanced isn't that big a deal on a PI. Especially audibly. I am surprised you hear a difference.

Note that he doesn't know if either tube is balanced, and doesn't know the strength of them.

There's a bunch of unknown variables there that could be audible.

 

[Jethro Rocker]

Note that he doesn't know if either tube is balanced, and doesn't know the strength of them.

There's a bunch of unknown variables there that could be audible.

Right.
Would the PI only be audible once it is pushed at high levels? I understood that the PI really didn't affect anything tonally at lower levels?

 

[RLW59]

V1 in most important for noise, frequency response, dynamic response to input signals.

PI doesn't do much In frequency shaping, but how it distorts is pretty important. It's a big part of what we hear as "power tube distortion". On an amp with a post PI master volume you can be pushing the PI quite hard at low volume.

It doesn't have as big an impact on tone as V1 but it certainly has some effect on tone, and different tubes in the PI can sound noticeably different

 

[Dave J]

Thank s to all of you, Mad Jack and Jethro Rocker too for your help in my other thread on the diodes as well !! I'm going t take all this advice and do some serious tube swapping this weekend. Set my head up on the cab backwards with the back grill off and go to town !

 

[snakej200]

This is gonna sound silly- but talking to other gear heads it’s is def a thing: make sure whatever conclusion you come to good bad or indifferent you arrive at that conclusion after hearing whatever it is you’re judging on several different occasions, specifically several different days.

I’ve found that what sounds absolutely magical to me one day will sound sterile and lifeless the next day only to sound magical again the day after. I can’t explain it but my ears play tricks on me. I make sure that before I come to a decision on something that I’ve felt that way on several different occasions.

Something else I heard on a hifi stereo YouTuber’s channel when talking about whether or not power cords make a difference: Don’t come to a conclusion after the “upgrade” whatever that may be. Leave the “upgrade” (in this case whatever tube you’re trying out) in and listen to it for say a week or two. Then go back to what you had previously. It’s a little easier to notice when something sounds WORSE than when you just spent $$ on something and you’re hoping it sounds better! Of course you’re going to think it sounds better!

 

[El Gringo]

So I have a Sovtek 12AX7-LPS that I picked up from somewhere a while ago ( might have been from Amazon?) and decided to put it in my PI slot of my Mini Jubilee. I have read that a Long Plate 12ax7 can be a good thing in that slot. My amp has the originial Marshall branded ecc83's in it now. It didn't sound better, maybe worse. Did some reading and learned that for the PI slot it's best to have a balanced preamp tube. I don't have the ability to test tubes for that so I assume the Sovtek is either just not a good one, is not balanced well or both.
Does Marshall aim to put a balanced tube in the PI slot? Or is it just whatever is next up in the bin, untested by anyone? These are the Studio series that are made in the UK so if in fact having a balanced tube in the PI slot is desirable, I'd hope they make that effort for the higher priced, UK made Studio Series.
I have a modest collection of 12AX7's, some old RCA and GE's given to me by a friend who was cleaning out his basement, as well as some 1990's Mesa branded 12AX7s ( one a SPAX7) that I can try in the amp. With no test equipment I can only go by how it sounds. The nice thing about the head is that it's easy to swap them. Also thinking about just getting a known balanced tube from a tube dealer so I know what I have. I can always try the other tubes in V1 and V2.

Why did you swap out the tube ? If it was working from the get go ?