How do I know which tube goes in V5?

[rockhound76s]

Please excuse my ignorance...

I just received a shipment of tubes for my Mark IV (a set of JJ's), and after removing all the tubes from the packaging, I realized that all 5 preamp tubes look identical, and I don't know which one is the phase inverter V5 tube.

I've previously only used Mesa tubes, and the V5 tube has always looked different from the other four.

I looked back at the empty preamp tube boxes, and one of them is labeled V5/Phase Inverter, but I don't know which of the 5 it is. Is there a way to easily tell, or do I need to find someone with tube testing equipment?

I thought I'd ask the board before risking putting the tubes in the wrong slots.

 

[Guitarzan]

It should have a metal shield over it... Go to Mesa's website and look up the Mk IV Manual if you don't have it or if you do look at page 21.

 

[phyrexia]

edit:fooey

 

[rockhound76s]

Guitarzan, thanks for your response, but I think I may not have been clear in my original post....

I have the tube task chart handy, so I know where to put the tubes. But the actual JJ preamp tubes look identical and one of them supposedly has a different rating to be used in the V5 slot.

 

[rockhound76s]

OK so I edited my original post, I meant to talk about the V5 tube, not the V1.

Sorry for the mixup

 

[Guitarzan]

Guitarzan, thanks for your response, but I think I may not have been clear in my original post....

I have the tube task chart handy, so I know where to put the tubes. But the actual JJ preamp tubes look identical and one of them supposedly has a different rating to be used in the V1 slot.

Problem solved...

 

[phyrexia]

The phase inverter tube does not need to be different in any way, but many times the phase inverter is a tube that is matched on both sides. So if you have a tube tester, you could test both sides of each tube and choose the one that tests closest to being matched.

 

[Guitarzan]

+1^ Thanks Phyrexia.

 

[rockhound76s]

Thanks for the help guys, I'll visit the local amp tech and see if he can test out the tubes.

 

[rockhound76s]

Sometimes the ratings are written on the boxes too. Not sure in your case but when buying from Dougs Tubes he does this. For example the one marked 100/100 (or 105/105 or 95/95 etc) is for the PI.

Yes, this was the case here too. The problem is that I didn't realize that the PI tube box was labeled until AFTER I removed all of the tubes from their boxes. Now I am looking at 5 identical JJ preamp tubes, and have no idea which one was shipped in the box with the PI label.

 

[rockhound76s]

So I tried swapping in the JJ's one at a time into V1 to see if I could find one that sounded different, but no luck. They really sounded all the same to me---either that or I'm afraid I just don't know what to I should be listening for.

For the record, what IS the general effect of not having the "balanced" tube used in the V5 slot?

In any event, I'll be calling the shop later today to see if I can find someone with a tube tester.

This is one of those things that will just prey on my mind until I figure it out :evil:

 

[recto-robbie]

Another reason to shop with Doug,, not only does he mark each box with the different ratings,, he also marks each tube with its ratings.
Like GTS mentioned above, the marking that matches is your PI.
I guess all you can do is bring it to someone to test them.

 

[phyrexia]

Ok, in short, your power amp splits up the signal into two half waveforms. There are all the parts above the X axis (if you're looking at a graph of a soundwave) and all the parts below it. One side of the PI deals with one half of this signal, and the other side deals with the other half.

When the PI tube is matched, your power amp will have a little more headroom because there won't be any clipping by the power section. (Make sense? I am a little fuzzy on this part myself.)

So if you had a really raunchy non-MV amp that you wanted to break up quick (say a Bassman or something) you would want an unmatched PI tube, but if you had, say, a Triple Recto and wanted all the headroom and power you could get, a matched phase inverter would be your best choice.

Plus you spent extra money for that matched triode 12AX7.

 

[stokes]

Unless the two halves of the one of the preamp tubes are drastically mismatched,you wont notice any difference using the "matched" triode in the PI position.Matched triodes are more relevant in HI-FI use when everything is aimed at zero distortion.As you have already pointed out you cant hear a difference when switching the tubes around,so dont sweat which one is matched or balanced.In my experience and my opinion is that balanced PI tubes are a lot of hype,the 2 sides of your output tranny arent matched so the PI tube aint gonna make that much difference,and most matched power tubes are likely off by as much as 5ma's anyway.

 

[Guitarzan]

Did you get it figured out?

 

[Shep]

the 5 V is for the phase intverter..they " say " they need to be matched so you get the best responce..but as stokes said your output tranny isn't so why would the tube matter

 

[domct203]

Don't sweat the matched PI thing. The only concern I would have is if the tube that was selected for the PI ended up in V1, it may be noisy as it was not selected for audio amplification, but for Phase Inversion.

A 12AX7 (ECC83) is actually two tubes in one bottle. In the case of the PI, one side drives the "push" while the other drives the "pull" of a class AB amplifier. That's why power tubes are in pairs in an AB class amp. While one is pulling (-phase) the other tube in the pair is pushing (+ phase). In theory if the push-pull gets out of sync and fights each other, certian frequencies (notes) could get cancelled out, but the tube would have to be way off.

And as far as I know, the OT's purpose is to drive the speaker load, which is mono, so there is nothing to balance but impedence. The OT sees the sum of the pairs of powertubes, after the push pull amplification.

Dom

 

[stokes]

"And as far as I know, the OT's purpose is to drive the speaker load, which is mono, so there is nothing to balance but impedence. The OT sees the sum of the pairs of powertubes, after the push pull amplification."

This is true to some degree,but the primary still has 2 sides,from CT to one end and from CT to the other end.If you check the DC resistance from CT to either side you will see the primary halves dont match each other,so if one power tube is being pushed slightly more than the other due to an imbalance in the PI the OT could still end up cancelling or making a further "imbalance".Even with a balanced PI if you put a dual channel scope on the outputs of the PI you will still see a slight mismatch in the wave forms.This is likely due to the fact that the components in the PI circuit,as well as the rest of the amp,have a tolerance of +/- 5%-10% and even more.If you run a guitar thru a good quality tube HI-FI unit you will most likely not like the cold, sterile sound,this is because Hi-Fi uses a lot of precise component tolerances,a big part of the warmer sound you get out of a tube guitar amp is due to the "imperfections" and wider tolerance of the components.Of course there are some who swear by the balanced PI for guitar amps,and it is a matter of taste,and as rockhound already pointed out,he tried to hear a difference with different tubes in the PI,and couldnt.As domct pointed out,noise could be a problem,but I would hope that if the supplier went thru the trouble of matching for the PI he would also cull out any noisy tubes,but that might be asking too much of someone who may be more interested in his profit margin.

 

[domct203]

Stokes, good point with reference to CT on the primary side of the OT. And I agree, it's all the little "imperfections" that make each amp unique.

I guess the moral of the story is don't worry about which tube is where as long as it sounds good.

Here is a tip - take a Sharpie marker and write on the tubes what position they are in ( V1, V2 etc) so this does not happen again. I will also put a "1" on the bottom of any tube I have that sounds good in V1, as well as a "B" for the "balanced" tubes for the PI, even though I don't hear a differance between balanced vs. unbalanced as far as the PI goes. This keeps my growing assortment of pre-amp bottles organized.

Dom

 

[rockhound76s]

I guess the moral of the story is don't worry about which tube is where as long as it sounds good.

Dom

I'll drink to that, Dom!

So for the update....I tried to find someone local with a tube tester, but to no avail. But ya know what? I don't mind because the amp sounds GREAT!

I don't know if its because I randomly put the preamp tubes in the apparent "correct" slots or if the "balanced" tube really isn't that big a part of the sound...all I know is that there is no noise from V1 and the amp sounds much more dynamic and powerful.

The JJ preamp tubes, BTW, are a little dark in the Mark IV. I've had to tweak my presence control and treble/gain setting slightly to compensate. This is a matched hi-gain set from Eurotubes that also included two JJ E34L and two JJ 6l6GC for the power section.

Thanks to ALL of you guys for helping me out on this. If nothing else, I've learned a lot about tubes, to mark my phase inteverter tubes with a sharpie, and most importantly....when all else fails, trust your ears :idea: :wink:

PROLOGUE: By the way, I just wanted to say that Eurotubes was great to deal with and Bob was very helpful in answering my questions before I made my order. When he shipped out the tubes, the preamp boxes WERE labeled to avoid such confusion----I simply opened them too hastily and confused myself. I wanted to make sure that was clear, because dealing with Eurotubes was a first rate experience.