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PostPosted: Fri Nov 10, 2017 7:11 pm 
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Mark III

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can anyone tell me what harm, if any, will come to an amp if i use a regular ecc83s in the phase inverter socket instead of a tube that's meant for this position? it's a non-mesa amp (Orange) but i don't think it would really matter from brand to brand. i had a buggy tube and replaced it but i'm left wondering if it was the phase inverter tube or not since i can't find a tube layout chart for my model (Rocker 32).


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PostPosted: Sun Nov 12, 2017 1:19 pm 
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Dual Recto

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If you replace the tube with the same type (12AX7 ECC83, ECC83s, ECC803s 7025, CV4004 or other variants) it should be fine. However if the amp requires 12AT7 (ECC81) or one with lower gain 12AU7 (ECC82) or the lowest gain 12AY7 or other not sure what the impact will be. There are some rules to follow on tube variants.... I did a quick search and found this but there are other recommendations that state the same thing.... the basic rule is do not jump too far on the gain chart from the actual intended tube.

http://www.cydathria.com/fdm/12AX7_sub.html

There is also this reference but more info on tubes in general vs substitutions...

http://www.worldtubecompany.com/mm5/mer ... creen=TF-2

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PostPosted: Tue Nov 14, 2017 3:07 pm 
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Mark III

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I assume by "meant for this position" you mean a balanced triodes tube?

There will be no harm to the amp, but the tone might be affected. The general idea is because a phase inverter splits the signal, it amplifies the positive part on one triode, and the negative half on the other. If those triodes aren't balanced, then the top and bottom of your wave might be amplified differently and sound different. So a balanced tube (one measured to behave similarly on both triodes) would limit that.

Now, on the other hand, the distortion, the amp signal, or even the output from your guitar might not necessarily be perfectly symmetrical anyway, and those differences could be part of the magic. And many people have spent years replacing tubes without any idea or worry about balancing triodes yet still recorded classic tones.

So I would say first, there's no harm, and second, let your ears guide you. If it sounds good, then don't worry about it.

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PostPosted: Tue Nov 14, 2017 11:45 pm 
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Mark IV
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Of course, in some amps only one side of the PI tube is used...so balanced really doesn't matter...even then, it still really doesn't matter as everything else in the amp is not balanced...balanced preamp tubes is actually marketing hype made up by sellers to get more money out of the consumer for something that is not really needed or audible...I always say, "play more and stress less about tubes"

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PostPosted: Wed Nov 15, 2017 12:39 pm 
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Mark III

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thunda1216 wrote:
Of course, in some amps only one side of the PI tube is used...so balanced really doesn't matter...even then, it still really doesn't matter as everything else in the amp is not balanced...balanced preamp tubes is actually marketing hype made up by sellers to get more money out of the consumer for something that is not really needed or audible...I always say, "play more and stress less about tubes"


If only half of the tube is being used... it's not really a Phase inverter is it? But you're right that there are single ended amps that don't even use phase inverters or care a lick about balanced sound.

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PostPosted: Wed Nov 15, 2017 3:49 pm 
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Mark III

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IronSean wrote:
thunda1216 wrote:
Of course, in some amps only one side of the PI tube is used...so balanced really doesn't matter...even then, it still really doesn't matter as everything else in the amp is not balanced...balanced preamp tubes is actually marketing hype made up by sellers to get more money out of the consumer for something that is not really needed or audible...I always say, "play more and stress less about tubes"


If only half of the tube is being used... it's not really a Phase inverter is it? But you're right that there are single ended amps that don't even use phase inverters or care a lick about balanced sound.


There are different designs for phase inverters, some of which only use one half of a twin triode tube. The most common in guitar amps is the "long tailed pair" which uses both halfs of the 12ax7 (ecc83) tube. The "cathodyne" only uses one, opposing signals from the anode and cathode of the same triode. Thats the two designs i know of, i'm sure there are more still.

Just spent 5 mins googling the Rocker 32 ( cool amp ) and didn't find out which tube is the phase inverter, or even if it has one. A stereo power amp at 15w a side running 2 x el84's a side must be class A right? No phase inverter needed.

To the OP, go by the tube layout guide written on the back of the amp, as long as you've got ecc83's where its say to and ecc81's where it says to you're fine. Like mentioned before, any correct type tube will work fine, balanced, unbalanced is all down to preference and a very small difference anyway no matter which you prefer. No way is right or wrong.

I did notice that it has a cathode follower though according to the write up on the Orange website so certain modern production tubes might fail early in that position, couldn't tell you which position it is though i'm afraid.

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PostPosted: Wed Nov 15, 2017 4:34 pm 
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Mark III

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Wayno wrote:
There are different designs for phase inverters, some of which only use one half of a twin triode tube. The most common in guitar amps is the "long tailed pair" which uses both halfs of the 12ax7 (ecc83) tube. The "cathodyne" only uses one, opposing signals from the anode and cathode of the same triode. Thats the two designs i know of, i'm sure there are more still.


D'oh, forgot about those other designs. My bad.

Wayno wrote:
Just spent 5 mins googling the Rocker 32 ( cool amp ) and didn't find out which tube is the phase inverter, or even if it has one. A stereo power amp at 15w a side running 2 x el84's a side must be class A right? No phase inverter needed.


I tried finding a schematic to confirm, but I would say you're correct there. Not necessarily Class A (could be A or AB depending on the bias/power amp design), but with a single output tube per power section (left and right) it's got to be single ended. So no phase inverter required. Though, since it's stereo it might have a tube playing a similar role: splitting the signal between the left and right outputs but probably not inverting phase. I'd say possible issues with being unbalanced would be even less audible here. Very interesting though, you don't see stereo tube amps around much.

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PostPosted: Wed Nov 15, 2017 4:40 pm 
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Mark III

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i think its a pair of el84's a side? gotta be class A? Just read a review from the guitar magazine and they stated that one side of the stereo power amp is cathode follower driven and the the other is anode driven. High current and low voltage one side and vise versa the other. Apparently gives a 3d effect blending the two! Very clever design / idea.

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PostPosted: Wed Nov 15, 2017 7:49 pm 
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Mark III

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Very cool idea, yeah. And you're right, it is 2 el84s per channel. So at 15 watts and two el84s it's gotta be class A, push pull. So some form of phase inverter on both sides, plus the extra cathode follower on one side.

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