new here need help with powering a tube

[thebeezneez]

hey guys im new here. first time with tubes. i just need some help trying to figure out how i could hook up the power supply.

the tube im using is a 12av6 (this is 1/2 a 12ax7) the heater runs at 12.6v @0.15amps. and needs a 150v dc b+ rail for potential difference.
so my understanding is that starved tubes use a lower potential difference like 25v or even lower.

so can i use a starved voltage for a 25v b+ rail or even lower. or could i use a 150v multi-tap transformer for my higher voltage and push the tubes true colors?

so how would i hook up the heater? do both connections get a positive feed of 12.6v @0.15 or umm? lol

appreciate the feedback guys 

[antonis]

I'm a bit of confused about your queries so better study a - more or less - typical power/bias scheme...



A better/closer power scheme:
(substitute rectifier tube with any diode/bridge of your taste..)

[thebeezneez]

thanks for the schematic. but i need to know how to hook the tube up not a general schematic to go off. the tube is a 12av6 7 pin mini.

these are the only three questions i need answers to

1. my tube runs at a heater voltage of 12.6volt @0.15amps so do i have to hook up my heater to a 12.6volt connection at 0.15amps. (in lay-mans terms. what the hell do i hook the heater connections to and does it specifically have to be what the tube runs at in this case 12.6volt at 0.15amps)

2.can i use a voltage of 25v (b+ rail) or even lower for the tubes main power and is this called starved voltage?

3.i need to know how the hook this up in ANY SIGNAL PATH on lower voltages not in a amp running lethal voltages.


please do not post any more schematics guys i need solid answers to these questions. ive gone over pin outs and all of that. i understand that but no one can seem to just give me a strait answer to these question.

[antonis]

Solid answers are only given to solid-state queries.. !!!

I have to think about wellcome you..

[thebeezneez]

lol right on thanks for the help!

[antonis]

I should give a second try but, honestly, my English language skills don't help me to catch you.. 

[GibsonGM]

Why don't you build one of the more introductory tube projects, like the Valvecaster, that will help you understand how to connect the heaters?  You do need 12AU7 for that tho.

You must connect the heater to a 12.6ish volt supply, that is CAPABLE of delivering 150mA.   Pins 3 and 4, for 12AV6.  The tube will do the rest.  Devices DRAW current - they take what they want - you don't "give" it to them, you just make sure enough is available.  If enough current-capability is not present ("AMPACITY"), then your voltage is most likely going to drop when you try to draw too much from the supply.   

If you use an unregulated supply, use your meter to make sure you it 'sags' to bring the voltage down when loaded by the heater....open-circuit, it could be something like 16v if not loaded, which will burn the heater out.   In that case you need a big-wattage dropping resistor.

Or use a voltage regulator to give you 12V.   Some put a diode in the ground leg of the regulator to elevate it by .5V, optimizing it for 12.6V use.   But 12V is close enough for a heater.

If your power supply says "12V, 300mA", you will probably have excess voltage if trying to draw only 150mA.  See how this works?

Yes, you sure can run your tube on 25V in starved mode!  It won't give you as much headroom, but that may be exactly what you want.   One triode won't do more than some overdrive at best....when people do this, they will frequently use a boost before the tube (opamp, mosfte, jfet...) to drive it harder, so as to obtain tube clipping. 

Why don't you describe what you have for a power supply, exactly, and then we can tell you what you need to do to run your heaters? That would probably be easier...   

Welcome to the forum.   Here is the data sheet for your tube  https://frank.pocnet.net/sheets/093/6/6AV6.pdf

[duck_arse]

for antonis only! - you can cut and paste these and no-one will know .....

1) yes, you need 12V6 that will deliver at least 150mA. more current capacity is good, not bad, more voltage is bad, not better.
2) yes. 25V on a valve specced for 150V is running starved-plate. you can only try it, some valves are better at it than others.
3) any signal path is completely isolated from your circuits power supply [barring ground, obvs], so the signal path won't know or care what the plate voltage is - when done correctly, again obvs.

for thebeezneez - welcome to the forum.

[thebeezneez]

alright sweet guys! and thanks for the welcome! i did look up a couple schematics on how to hook up the heater but was confused because they never showed what they connect to lol.

i wanted to use this tube because i bought a all american five radio and figured this was a smaller project.  just to introduce me to tubes minus a couple things with what was on hand. i would love to get a kit eventually though.

i was not sure about having to many amps. so as far as the tube goes the amps dont matter?

i have a 0-30v digital variac for testing. theres def a lot of different power options ive looked at from 12v power brick to batteries to mini 24v transformers idk why but im stuck on 25v for this build but im not against making it a 12v circuit.

ive already considered adding a 100ohm resistor between power and heater because in this cause r=84 because the heater on this tube dies at 13.5ishv.... would that be a correct way to go about that if im running a 12v power?

DUCK_ARSE-what i meant by signal path was just to get the tube to produce sound sorry if im a little confusing. lol

[iainpunk]

Hey.

Most questions are already answered, but there is one think id like to add; the 12av6 is far less than ideal to make a starved plate system with. I have used the 6av6 (same tube, difirent heater) and had a very bad sound, i had to put in plate resistors if 2M2 at b+ =24v to even get signal that is not horribly farted out.

I recomend you get an 12au7 because it has far better starved plate characteristics

[PRR]

Licking the poison well of theory and experience.....

An old rule learned behind the barn (not in any book I've seen) is that B+ should be larger than Mu, the theoretical gain factor of a tube. If not, the operating point is uncertain and maybe unstable.

This really suggests that your grid voltage has up-to +/-1V errors of Contact Potential and grid current, plate voltage tends to be ~~Mu bigger than grid voltage, so you want enough B+ to handle that.

6AV6 is Mu of 100. The old timers would not work it with much less than a 100V supply. (A 90V suggestion is in the charts.) 6AV6 has a flock of friends with Mu of 60, 40, 20, etc, for when you want happy working rather than extreme gain.

But guitar-tone is a funny world. Many experimenters have messed with very low voltage. Also the old rules may be upset by low-price chips to buffer. Old Days, we always wanted negative grid because positive grid sucked signal from the tube before. A 19 cent chip can drive all the suckage of a 12AV6/12AX7 grid at any voltage. Is this "true tube tone" like a 1947 Fender? Well, who remembers?

A mildly popular Fender uses a twin-triode as a dual-diode clipper around an opamp. Merlin has done some work on tube diode curves. I have a feeling that, blindfolded, you could not tell this from a nice crystal diode clipper. But we don't play blindfolded, and knowing "there is a tube in there!" may inspire your playing.

[thebeezneez]

PRR- ive had many people tell me that the tube running at less than recommended isnt wise for this particular tube. the radio i pulled it out of is using 150v b+. im still learning how to run a positive or negative grid.

i will probably be adding a boost circuit to get a better sound out of the tube or using a extra pentode tube in a preamp stage or something along those lines.

[GibsonGM]

If you're going to go to the trouble, why not obtain 1 or 2 12A*7 duo-triodes?  For the effort you'll do, you could make a GREAT preamp with 2!  I mean REALLY great.   Look up the "GTFO" on here. 

It's understandable to want to use the 12AV6 in something like a simple boost, to USE it, make something cool....an input stage to drive it, Mosfet or opamp, etc...is a good idea IMO.  You will get something cool out of that without a lot of time laboring and doctoring power supplies.   Once you go beyond the one tube, again my opinion, you start to run into an area where "hey, I would've done better to get a real transformer with heater supply, this is work and for the same work I could've sounded like Slash!  I made a whole 12V supply for the heaters, and it's only ONE tube??".   But whatever works for you.

I don't know what you mean, positive or negative grid?  It's supposed to be negative...drawing grid current (grid going positive) is a bad thing IF done to a large degree.    Excursions create nice compression and this is desired, tho...which again, an input stage may get you if you bias closer to zero. 

Pentodes can be hard to set up and noisy if you're not familiar w/tube construction...

[thebeezneez]

posivite or negative grid-im still learning this term and the main function on tubes.

in the 1950-60s the ac-30 used a petode for better tone on a positive grid system. im fully aware pentodes pick up more unwanted freq, partitioned noise and are not to ideal.

but then theres this amp i love the line 6 dt-50 with triode/pentode (el84s). the tone is amazing. the distortion is unbelievable. to get around unwanted noise would be to use the pentode in a later stage. they have a better tone and the can be driven better. i wanted to run it ultrlinear which is positive feedback from grid. (again this part is theorectical. ill probably just go with opamp or somthing simple until i get the hang of work with em.)

[GibsonGM]

Yes, you're right - you can get very nice results with a pentode, especially if you use is as a second stage or something like that!  What I mean is that they are not always the best choice for an input stage.  The AC-30 is a fine amp, and I would trade guitars to own a real vintage model 

Typically, the grid is held more negative than the cathode - this is the function of the cathode resistor.  This accelerates electrons toward the anode; without this (differential), the tube can't work.  Not trying to insult, only to explain the basics of tube operation.   Do you have more information about positive bias?   What is important is that the grid be more negative than the cathode - the differential is important, not the actual voltage measurements.     I'd like to hear more about positive bias....

[Phoenix]

Welcome thebeezneez

i wanted to use this tube because i bought a all american five radio and figured this was a smaller project.  just to introduce me to tubes minus a couple things with what was on hand.

Just wanted to mention because no one else has so far, DO NOT try to restore the All-American-Five radio until you have some more experience, they are literal death-traps due to their lack of power transformer (no galvanic isolation from the mains power). They MUST have an isolation transformer added in order to be safe. Once you have some more experience it will be a good project, but at this stage you would be putting yourself (and potentially others) at serious risk.

Good luck with your project.

[thebeezneez]

phoenix- im aware it doesnt have as transformer and is lethal i already opened it up and removed the caps and tubes so unless i plan on touching a bare wire i think its relatively safe for now. and im not by any mean restoring this. just decided to use it for parts. but thanks for the heads up!

[Phoenix]

Mike, positive grid is not a normal mode of operation for receiving tubes (it is sometimes used in transmitting tubes), though the grid can go positive relative to the cathode during parts of the signal swing, and if the source impedance of the driver is low enough, this can allow class A2 (or AB2/B2) operation, allowing the plate to swing lower than it normally would otherwise be able to, getting more voltage swing out of a preamp tube, or more power out of an output tube. However, even this is not very common in guitar amps, typically only seen in high power bass amps like the massive Fender 400PS.

The Vox AC30 (only the very early versions sported the EF86 input, it's the AC15 that's better known for that) does not operate with a positive grid at all - both it and the AC15 have standard cathode biased negative grid.

[thebeezneez]

yeah the schematic i looked at were off the input stage of the ef84. way in the early years. (like i said my terminology is iffy lol) but i started to read more information on it an got the same information about higher output. and also can do used to draw power from a tube.

[GibsonGM]

I know, Phoenix...I just wanted to see if Beez was looking at something that would be interesting.  We want the grid referenced to zero and the cathode elevated a bit, per our characteristics...and when excursions begin to make it draw grid current, some nice things can happen.  And if that is taken too far, some very NOT nice things happen, LOL!  Grid compression is useful for just that...compression.  Then you get into grid current limiting, and all of a sudden, your design sucks.

Phoenix is entirely right.   I say, you should start off with an "introductory" tube circuit, even if you have to buy a 12AU7 to start.  Valvecaster or some such thing.   This'll get you working on power supplies, understanding Ohm's law and current, power ratings of your parts.    It's important for later work when you start with the EF86's!  One of the best projects someone can do is to plan out what the want, design the thing, set up the power supply, and make it all work!

The tube 'things' are relatively easy, IMO (designing a preamp)...getting the power supply together so no bad things happen is the hardest work, for me.   

Have you looked into any resources about how tubes work to amplify? We don't know your background, so tell us how advanced you are!  No shame, everyone starts somewhere, and tubes are an old secret magic thing that takes work to understand!