new here need help with powering a tube

[thebeezneez]

in that case ill probably buy a 12ax7.

my background-ive built a bunch of ss pedals and smaller amps. id say it ranges. ive done some very simple things like rat distortions. anolog delays and effects. simple amplifiers. all the way to stuff like the lm386 electrosmash and more complex builds.. for me ss is relatively easy and ive gone off to just design my own stuff. i understand ohm's law and current i just havent work with higher volts. i guess the tubes are throwing me off because its totally different and new to me.

i have looked up tons of information about tubes. how different tubes operate like rectifiers, triode, heptodes, beam pentodes, ect. and how they function differently. i just havent had anyone to talk with or ask question so i have tones of information and ideas about the subject but no exp 

[Phoenix]

in that case ill probably buy a 12ax7.

A 12AU7 (ECC82) is a better choice for low-voltage operation than 12AX7 (ECC83).

[GibsonGM]

Yeah, it's sort of a lonely world, ha ha!   But you're not alone! Start here:    http://www.valvewizard.co.uk/gainstage.html 

You may find your need to figure out dissipation of components (watts) starts increasing, when you up the voltage...I know that happened to me (heater supplies, dropping resistors...)! 


Regarding low voltage common tubes, yup, 12AU is better.

[thebeezneez]

i guess im just stuck on the 12ax7 for the distortion qualities lol i am after all a metal player. but ill probably by a couple different dual triode tubes just to hear the sound difference.

[thebeezneez]

gibson dude thanks for that link the first little bit of it explains a couple thing way better than some of the information i had.

[Phoenix]

i guess im just stuck on the 12ax7 for the distortion qualities

A 12AU7 can distort just fine, 12AX7's are just useful when you need a lot of gain to clip with high voltage rails. When you've got low voltage rails, a lower gain 12AU7 can easily have enough gain to clip

[GibsonGM]

In my GTFO, I replaced V1 (tubes are called "V" on schematics) with a 12AU7.   Running on about 240V, a little low for 12AX7, the AU was a little "creamier", less harsh, IMO.    So they all have their purposes.

AU7 has a bit lower gain characteristics than AX7, but sources current better, behaves better at a lower voltage...a good candidate in many places such as buffers ("cathode follower") for tone stacks, cascodes...remember, you may have 60V at V1's output in a preamp...it's how you use that 60V to hit the next tube that really matters! 

[PRR]

The NuTube is only useful with positive grid. Does not pass hardly any current neg-grid.

The pos-grid current is tiny (in accord with the whole thing, which was NOT made to be an amplifier tube, but a low-power display). While a 12AX7's grid falls to <1K in pos0grid, the NuTube may only go to a few K. That's still far too high to connect to the many-many-K  output of another NuTube. But it is an easy load for a 19 cent chip.

Having "a tube" does not get you very far to "a tube amp". Tubes are almost never the largest part of the cost. I spent over $500 on my last 2-tube project, of which $130 was tubes, including 3 alternates for one socket.

[thebeezneez]

http://www.valvewizard.co.uk/pentode.html
https://www.ampbooks.com/mobile/tutorials/pentode-tutorial-1/ - this is why i mentioned using a pentodes.


http://www.vias.org/crowhurstba/crowhurst_basic_audio_vol3_027.html -and this is the article that mentioned positive grids

can someone please explain why they use the term (positive grid).

[antonis]

can someone please explain why they use the term (positive grid).

Because Grid isn't biased to negative voltage (relative to GND)..
(Cathode is simply voltage off-set in relation with Grid voltage..)

It works just like JFETs bias (actually, JFETs bias works like Tubes bias..  ) where the only interest is the Voltage difference between Gate - Source (Grid - Cathode) so can both be positive..

[thebeezneez]

i guess i was just confusing the term. i was reading somewhere that with pentodes running ultra-linear. the voltage swings above on self bias. just like what ppr was talking about (ab2 operation) and im pretty sure i was confusing it. i understand that the grid is negative compared to the canthode (doesnt matter if its positive as long as its a lower v than the canthode?)

so what are the benifits of a having negavite (grid) ? and the benifits of running a positive grid but still lower v than the canthode? does it have any affect or not so much?

[antonis]

<doesnt matter if its positive as long as its a lower v than the canthode?>
Strictly speaking, no it doesn't..

<so what are the benifits of a having negavite (grid) ? and the benifits of running a positive grid but still lower v than the canthode?>
Headroom..

The higher the Cathode voltage the less the availiable undistorted signal swing..

[thebeezneez]

so exactly like ppr said if you want to run a pentode positve grid you could get past that by getting a chip that can controll the suckage and off-set of signal swing. i get it.

[thebeezneez]

so my other question is-

would i be able to run a positive pentode grid with low impendence to get a higher output from the pentode im using. can i then use that and drive my triode. my understanding is that theyve used this with early amp models to produce that true tube sound ppr was talking about in the 1940s fender amps.

[printer2]

You are trying to run when you have not learned to walk yet. This positive pentode thing is only relevant to output tubes trying to get more power out of the tube when supplied by a lower voltage (more or less). First, how is your Ohm's law, series and parallel circuit theory? You need to have some concept of why a certain part will draw a current from the supply. Among other things. Read this and then read it again.

https://www.ax84.com/p1/P1_Theory_Document.zip

[GibsonGM]

Read on Merlin's site that I linked for you earlier, about triode gain stages...you could buy a book too!   And Printer's link, AX84 is a great reference.   

The 'normally configured'  (cathode-biased) triode gain stage is the foundational building block for the entire 'tube world'.  Without understanding it, you probably won't ever be able to really understand what's going on in an amp.  Let alone come up w/a successful design.

Pentodes can be fussy, noisy and a poor choice for input stages.  Learn the triode first, as completely as possible.  Including power supplies.   It is not as hard as it seems at the beginning.  Ohm's law before anything.  Load lines.   Build simple 1 tube, low-volt things like the Valvecaster...move on to more advanced projects later. 

If you don't want to do that, then you might just follow an existing project, build a kit or something, because you won't know enough to design anything.

  But please at least learn about line power safety if you don't already have that knowledge!   

[antonis]

Read on Merlin's site that I linked for you earlier, about triode gain stages...you could buy a book too!   And Printer's link, AX84 is a great reference.

I think thebeezneez wants solid answers with no scematics/links/theory, Sir...

[GibsonGM]

Maybe. But then we are designing the circuit for him, no?  No schematics?  That is like communicating with no language        

It is hard to describe something pretty advanced, if someone does not know the basics, you must agree, Antonis.....now, if he wanted to begin with tubes, or with understanding Ohm's law,  this would be a good way!   To help with the power supply design, and a gain stage...simple things. 

It seems that we are beginning somewhere around page 100 of the Great Tube Manual