#1
I've been looking around various forums to find out what makes a good PI tube and the differences that various types of preamp tubes can have (i.e. 12AX7 vs 12AT7) but I can't really seem to find a good explanation that explains everything well enough.

Currently I understand that the Phase-Inverter has very little effect on tone and a 12AT7 will change "output tube distortion, touch, and output dynamics in most amps"

Also, I've read this article: The most important tube in your amp?

Is there anything else I should know?

The amp I'm planning on tube-swapping is a Peavey 6505+ 112 Combo. V1 will have a Tung-Sol and the rest will be JJs apart from the PI, which I need some help with. By the sounds of it a 12AT7 would be my best bet unless there are reasons why I wouldn't want to do that.

Thanks,
Miles.
Last edited by MilesJeffery at Feb 2, 2014,
#2
I have a JJ 12at7 in the PI of mine. It will reduce some fizz and more importantly, give you better, warmer cleans. Do it.
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#3
I've noticed the fizz too. At first I thought it was just the presence too high or the treble up too much. Thanks for the suggestion!
#4
I use a JAN GE 5751 or Sovtek 12ax7lps for my PI tubes. the 5751 has more gain than the 12at7 but less than a typical 12ax7. The Sovtek 12ax7lps is really nice for the PI and is not fizzy.

The PI can have a noticeable affect on the tone of your amp
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#5
Quote by KailM
I have a JJ 12at7 in the PI of mine. It will reduce some fizz and more importantly, give you better, warmer cleans. Do it.


Same effect on Valveking. 12AT7 as PI makes the amp sound cleaner. If this is a desireable attribute is a matter of taste. I prefer 12AX7 in Valveking myself.

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#6
Quote by MaaZeus
Same effect on Valveking. 12AT7 as PI makes the amp sound cleaner. If this is a desireable attribute is a matter of taste. I prefer 12AX7 in Valveking myself.


When you say 'sounds cleaner' do you mean that there's less gain so I would need to turn up the preamp gain slightly more or do you mean that there's less extra noise and fizz?
#7
Quote by MilesJeffery
When you say 'sounds cleaner' do you mean that there's less gain so I would need to turn up the preamp gain slightly more or do you mean that there's less extra noise and fizz?


I cant really put it accurately into words but the I dont think the actual amount of distortion changed much but the nature how it sounded. Thinner/smaller and cleaner is the best I can do from hazy memory. It has been a year since I tried it, for couple of hours only. (during the time I had tube problems with the Valveking)

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#8
Quote by Robbgnarly
I use a JAN GE 5751 or Sovtek 12ax7lps for my PI tubes. the 5751 has more gain than the 12at7 but less than a typical 12ax7. The Sovtek 12ax7lps is really nice for the PI and is not fizzy.

The PI can have a noticeable affect on the tone of your amp

+1

I swear by the JAN Phillips 5751 for the P.I. Same thing basically as what Rob said. JAN = Joint Army Navy and is Milspec NOS. Low noise and the perfect balance between an AX7 and AT7.

Lots of people swear by the Sovtek 12AX7LPS for their Peaveys but I have no direct experience.
#11
Quote by 311ZOSOVHJH
+1

I swear by the JAN Phillips 5751 for the P.I. Same thing basically as what Rob said. JAN = Joint Army Navy and is Milspec NOS. Low noise and the perfect balance between an AX7 and AT7.

Lots of people swear by the Sovtek 12AX7LPS for their Peaveys but I have no direct experience.


I liked the JAN in 6505's and other amps. Great tube in the PI but it all depends on personal preference and what you are after.

I liked the LPS in the v1 slot for my 6505 and never tried it in the PI.
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Last edited by R45VT at Feb 2, 2014,
#12
There's a difference in the way they behave, the phase inverter is the tube that diverts current between pairs of power tubes. A 12at7, though lower in gain than a 12ax7, actually has a much higher current rating. This means it can handle more signal before it starts to break down, hence a perceived 'cleaner' tone. It's generally a tube that was DESIGNED for that position, though other tubes can also do it the different (not necessarily worse) extents. The ability of the tube to handle higher current values also means that more volume can be yielded from most amps (most notable of which are non-master volume types) because the tube doesn't break down as quickly, it allows more current to be transferred to the power tubes. This also aids in the acquisition of power-amp distortion, because the power amp itself is allowed to translate higher volumes than it would see if you had a standard 12ax7 type valve. Most amplification has already taken place by the time your signal reaches the PI, so gain really doesn't enter into the equation - it becomes more of an argument for lowering headroom and allowing for maximum pre amp distortion for dirty tones at lower volumes. A 5751 is a good tube because it's current values are higher than your average 12ax7, but lower than a 12at7. As with most things it's a matter of taste, which is always a pain when it comes to questions like this; but I am an advocate myself of a 12at7 PI tube purely due to my use of fender amps. Hope this helps.
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Last edited by DeviousByNature at Feb 2, 2014,
#13
The Sovtek seems a good choice, actually. I'll get a JJ 12AT7 and a Sovtek 12AX7LPs.

Also, I read in a couple of places that JJs are rebranded RUBYs so I was wondering if it would be a good idea to just get other RUBYs if they're cheaper than JJs or could someone recommend another preamp tube for the remaining positions? I would use Tung-Sols in the remaining positions but I heard that it could make the sound thin and overly bright.

Recommendations for power tubes would be helpful too.

I can afford to buy one or two extra tubes but not three of each just to test them out in the other positions. I'm on a student budget right now, unfortunately.

Thanks again,
Miles.
#14
No JJ is the company, Ruby rebrands lots of tubes and they do rebrand the JJecc83 I have bought a few.
I like the new Mullard 12ax7's I have one as V1 in my DSL100 and JJecc83 in the V2/3 positions.

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GFS Greenie/Digitech Bad Monkey
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MXR Smart Gate
#16
Another vote for the JAN Phillips 5751. If while you're searching for a Phillips, you see a nice RCA 5751 or 12AT7 at a decent price, grab it.
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#17
Quote by DeviousByNature
There's a difference in the way they behave, the phase inverter is the tube that diverts current between pairs of power tubes. A 12at7, though lower in gain than a 12ax7, actually has a much higher current rating. This means it can handle more signal before it starts to break down, hence a perceived 'cleaner' tone. It's generally a tube that was DESIGNED for that position, though other tubes can also do it the different (not necessarily worse) extents. The ability of the tube to handle higher current values also means that more volume can be yielded from most amps (most notable of which are non-master volume types) because the tube doesn't break down as quickly, it allows more current to be transferred to the power tubes. This also aids in the acquisition of power-amp distortion, because the power amp itself is allowed to translate higher volumes than it would see if you had a standard 12ax7 type valve. Most amplification has already taken place by the time your signal reaches the PI, so gain really doesn't enter into the equation - it becomes more of an argument for lowering headroom and allowing for maximum pre amp distortion for dirty tones at lower volumes. A 5751 is a good tube because it's current values are higher than your average 12ax7, but lower than a 12at7. As with most things it's a matter of taste, which is always a pain when it comes to questions like this; but I am an advocate myself of a 12at7 PI tube purely due to my use of fender amps. Hope this helps.


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