PHASE INVERTER

[TheHunter]

Does anyone know if the PHASE INVERTER tube needs to be balanced or does it matter much?

D

 

[nikki-k]

Hi!
This is a good one... and like so many things, can end in an endless debate.

It depends on the type of PI being implemented. If it is a long tail, then some will swear on using a balanced triode tube. Since 12AX7 tube types (C4004, 7025, ECC83, ECC803, etc) have two tiodes in each tube, the long tail PI (as an example) will use one triode for one signal, and the other triode for the "flipped" or out of phase signal, both of which are used in a push-pull (Class AB) type power section.

So, by having both triodes balanced, they produce (close to) identical results being sent to the power section.

Some will swear by having this situation if at all possible. For them, "balanced sounds better" or at the very least, produces a more *pure* sound/result. Now comes the caveat.. First, just because a tube is not tested for the triodes being balanced, it does not mean they are not, in fact, close enough. Second, just because they are balanced today, does not mean they won't be months from now. Third, I think the chances of IDENTICAL triodes is so incredibly rare. Fourth.. well, tubes are random by nature. Electrons have the biggest party in them, and who knows what they will do, beyond certain properties within "x" and "y." IOW, sure- feed it "X" voltage/current to produce "Y" result. Those "X" and "Y" figures are not exact numbers, but rather Ranges.

I have had amps that could care less, and sounded great by simply throwing a high quality tube in the PI spot. My Legacy is an interesting animal, as for me it loves either, and the result shows it. I have popped a non-tested Tung Sol 12AX7 in there, and it was beautiful with the rest of the tubing I had. But, I now have JJ ECC803S balanced in there, and with a gold pin JJ ECC803S in V1 (not balance tested), it is a beautiful thing. A JCM800 I had seemed to only want balanced.

Sorry for the wicked long reply.. But, in the end, it is all in the ears and fingers. Does it sound and feel good to you? Balanced simply means the tube was found to have two triodes close in result. I personally would not want a tube with one triode wicked hot, and the other wicked cold (pretty unlikely). I usually begin with a balanced PI, and once I get things the way I like, I might try random tubes, balanced or not. Imbalance is not always a bad thing

 

[TheHunter]

Thanks for the detailed responce It really helps to know these things, nad in detail is much better than a vague answer.

Thanks.

 

[droptrd]

That is some GREAT INFO! But, testing for a balanced tube is usually around 2-3 dollars. Thats 3 bucks for peice of mind. Id just spend the $3 and have one less thing to worry about.

 

[nikki-k]

Hi!
Thx
I would really suggest to anyone who even just uses a tube amp regularly to grab a good book. Scouring the web is one thing, but I guess I am old fashioned... I love having a book to open and have available, old and worn, bookmarks and highlights "The Guitar Amp Handbook" by Dave Hunter is pretty easy reading. Color photos of chassis innards, some schematics, layman's explanation. Move on to more detailed, technical and opinionated books from there.. IMO.

Going off track here a little, but I am a HUGE believer in knowledge. I know too many people who are afraid of tube amps due to high voltage, and also those who have NO fear, both due to the same ignorance. The latter is more likely to end up dead because of it. Just as with a handgun (or other weapon), understanding and educated walk-thru is invaluable. No amount of knowledge will make you immortal; but, it will give you a better fighting chance!

 

[nikki-k]

That is some GREAT INFO! But, testing for a balanced tube is usually around 2-3 dollars. Thats 3 bucks for peice of mind. Id just spend the $3 and have one less thing to worry about.

Hehehe.. yeah, I agree (in general). But, there are different PI types, and even if one had a long tail (pretty popular) or other circuit using both triodes of the PI in parallel (essentially), some will argue that due to the way the circuit works, balanced simply does not make a difference. Therefor, in their eyes, that is a wasted $3. Compiled over a lifetime for a tube lover that keeps a pretty full lunch box, it equals a couple hundred dollars (at least).

I like to have "known" balanced tubes of various makes and types,but also have those that are not tested for balanced triodes. Knowing is definitely nice (for me). But, it has, and will, not ever prevented me from popping an untested in a PI socket Sometimes it is nice to have the amp reflect the owner.. and being unbalanced myself..lol..

 

[TheHunter]

Well since im upgrading the tubes in my RM100 anyway I went ahead and got a balanced JJ ECC83s, so whether or not it makes a huge difference it was only 2 bucks for the re-assurance. I actually saved money going thru TUBEDEPOT.COM versus EUROTUBES.COM and still got the balanced tube and it was 5 dollars cheaper for the same exact thing for the total order.

Tube Depot has really cheap shipping as well, Euro tube charges out the ***.

D

 

[nikki-k]

Hehehe- Eurotubes is about a mile or so from my house

If you get a chance sometime, try a balanced JJ ECC803S. Go gold pin if ya like! I love the gold pin JJ ECC803S in V1 sometimes. Sweet long plate goodness

 

[okstrat]

One thing to keep in mind too is that the whole 'replace the phase inverter when you replace power tubes' thing is crap too. Preamp tubes last a really long time... I have some from the 50s that test stronger than new tubes.

Pete

 

[droptrd]

One thing to keep in mind too is that the whole 'replace the phase inverter when you replace power tubes' thing is crap too. Preamp tubes last a really long time... I have some from the 50s that test stronger than new tubes.

Pete

So do you recomend just replacing v1 v2 and v3 and leaving the pi and the buffer? (or in the case of the rm100- just replace v1)

 

[nikki-k]

Not speaking for Pete.. offering my 3 cents

As Pete said- preamp tubes typically last a long time. I have found reports of newer stock not having the same life as older tubes did. I have Brimar ECC83's (Made in Britain) from the 70's that are beautiful. Pete mentioned tubes from the 50's being as good/better today!

Power tubes, OTOH, are subject to greater wear and tear and typically will not have the same survivability as the preamp tubes. Bias a little warm, play ALOT at higher volumes, and yeah- those power tubes will "wear out," sort of. Some of us prefer a "broken in" power tube. I prefer broken in tubes all around. But, eventually, power tubes will sometimes go beyond "broken in."

So, with all that in mind, power tubes will require replacing. But, unless there is a problem with the preamp tubes, there is NO reason to replace them when the power tubes are replaced. Some people will say replace the PI tube when the power tubes are replaced. The PI tube is part of the preamp section, but also part of the power section. Hence, some feel it should be treated as a power tube is. It is not a power tube tho, and does not need to be treated as one. In fact, it might be getting better with age!

I personally treat the PI tube as part of the preamp section. And while power tubes are (typically) best treated as a whole (pair, quad, etc), preamp tubes are best treated singly IMO. Mix 'em up! Learn what they do, learn what each one's function(s) are in your amp(s), and learn to recognize when and which preamp tube may be "hurting" your sound.

 

[CHASENTONE]

I know this reply is better late than ever but, I just wanted to say thanks to Hunter for asking this question.The answer to this topic has eluded me for the longest time.Thanks to the people who answered here.It is a great privelage to be a part of this forum. 8) 8) 8) 8) 8) 8)

 

[Mailman1971]

I know this reply is better late than ever but, I just wanted to say thanks to Hunter for asking this question.The answer to this topic has eluded me for the longest time.Thanks to the people who answered here.It is a great privelage to be a part of this forum. 8) 8) 8) 8) 8) 8)

This is why I love this forum! I have had so many questions answered and everyone is so cool! I learned alot and shared alot with members here.
No snobs or uppity bastards. Just cool folk who want to talk amps and tone!
LONG LIVE RANDALL!

 

[MikeT]

Regarding the original question, I recall reading a simlar thread on the Metro Amp Forum or HRI where it was said that for a guitar amp and for the purpose of guitar tone - unbalance PI is better.

Mike

 

[skeeterbob]

Just to clarify the PI in an RM100 is the one closest to the power tubes right?

 

[CHASENTONE]

Yes.