Tube boost + overdrive running off a 9 volt battery

[idiot savant]

Neat thread Dano, and a neat design.

I really think there could be a whole lot more submini tube designs around. I' have a couple ideas ready for testing around the old Raytheon CK series tubes. they are mostly pentodes, but you can find the odd triode too. I'm planning a small 65mW all tube amp using a 5672, and a 5678 60-ish volt B+. the only real problem with 'em is the unusually high plate load required. the 5672 needs something like 20k, but Fred Nachbaur's "baby bear" using a 533ax would need 80k to get its 1.8mW; but could realistically run off of battery power(only drawing around 32-ish mA).

have a look at these submini monsters for ideas:

http://www.dogstar.dantimax.dk/tubestuf/gallery4.htm

scroll down to the "baby bear" using those teeny tubes even smaller that the 6111's and 6021's

as well as:

http://amps.zugster.net/

the submini section is really good!

[dano12]

Here's the updated schematic, this one includes the pin numbers for the 6111 in addition to the 12AU7. I've built and verified both.

[earthtonesaudio]

This is really helping me to better understand tubes, so thanks for sharing the knowledge!

So can this circuit do clean (or near-clean) boost?  And would it be possible to use both triodes in push-pull type configuration at such a low voltage?

I've been getting my micro-tube-effect education from the Vox Valvetronix and forum member Brett so far, for the most part.  Thread here:
http://www.diystompboxes.com/smfforum/index.php?topic=64053.msg505674#msg505674

[ambulancevoice]

i have an idea
what if, you use a 12ax7 as the main tube, and a 6111 wired as output clipping diodes?

[Krinor]

I'm not really very knowledgeable about biasing tubes, but I suspect using an AT7 or AX7 will require resistor value changes.

Just a few thoughts from someone who knows even less;

Would it not be possible to put in a trimpot in place of the plate resistor for each stage of the triode for biasing purposes ?
It would be interesting to be able to use the ax7, au7 and ay7 since they are relatively abundant. And maybe running the cicuit at 18 volts ? As far as I know the 12ax7 is supposed to have a plate voltage of 100, but I guess at least something will happen even at as little as 18 volts ?

And another question; are these triodes self biasing in a circuit like this ?

Maybe it's time for a sub forum for high voltage stomp box building ? With the proper warnings and disclaimers posted in front I guess such a forum could become a valuable addition to this site and a great learning resource and symposium for further experimentation.

Here's a resource for those (like me) who need to learn some triode fundamentals:

http://www.angelfire.com/electronic/funwithtubes/Basics_04_Triodes.html

[Papa_lazerous]

Maybe it's time for a sub forum for high voltage stomp box building ? With the proper warnings and disclaimers posted in front I guess such a forum could become a valuable addition to this site and a great learning resource and symposium for further experimentation.

not a bad idea, there is a forum dedicated to valve stuff www.ax84.com springs to mind there are others though

[Krinor]

Hey John, yeah I've seen a few (the one you mentioned, and also the great 18watt.com site and others), but I kind of like it here. And we would also keep the main focus on stomp box related stuff instead of going into tube amps which I guess is a bit outside the scope of this site. Hey Aron, how about it ? "Building your own high voltage stomp box" ?  Sorry, I'm drifting off topic. Back to Dano and this great little booster.

[brett]

Hi
I'm just guessing, but I notice that the 12AU7 has low internal resistance.  Only 10 to 15K, compared with 60 to 80k in the 12AX7. Given the low gain of both devices at these voltages, the low internal losses of the 12AU7 might help this critter work. A buffer might be useful at the output (e.g. a JFET source follower).

Vox gets reasonable tones from a 12AX7 at 15V in their Valvetronix series, but they use even higher loads (330k).  And, yes, they do have an option that uses both triodes in a push-pull arrangement.

great work 

[bancika]

Vox gets reasonable tones from a 12AX7 at 15V in their Valvetronix series, but they use even higher loads (330k).  And, yes, they do have an option that uses both triodes in a push-pull arrangement.

Isn't that a 12AU7 in vox pedals?

[dano12]

My knowledge of tubes and how to use them basically consists of hooking them up according to various schematics and seeing if they work. I'm about 50/50 on the success rate. I've been doing a lot of reading, but 99% of it is still a mystery to me.

Here's a really interesting idea from a guy who used a 6111 for a headphone amp. It uses a 555 and a voltage regulator to get the correct heater voltage and B+: http://headwize.com/ubb/showpage.php?fnum=3&tid=5878

[dano12]

In the continuing saga of my 6111 submini tube fetish, I tweaked this some more. After some breadboarding and measuring, it was clear that the 9v source in the previous schematic, as it relates to using the 6111, doesn't work well:

- The heaters call for 6.3vDC. At 9 volts on the previous schematic, they aren't going to last too long
- 9v was simply not providing enough boosth. So I bumped the supply up to 12vDC

To get a nice stable 6.3v heater voltage, and to add a little bit more control, I put together a power supply based on the LM317 adjustable voltage regulator. In combination with a 1Kohm pot/trimmer, I can tweak the heaters to as close to 6.3v as I want. I also added R1/C1/C2 to add a bit of noise reduction to the power supply. Note that the LM317 is going to get really hot, so slap a heat sink on it. You can get the 317 at Radio Shack, it's that common. Adjust TR1 to get 6.3v at the 'heater' connection.

Here's the schemo:


And a picture on the breadboard:


The end result with this new tweaked design is that it offers a substantial increase in boost over the 9v in/heater design, and the overdrive sounds a lot nicer.

[Krinor]

Wow, that looks very promising.
Now I just wonder if this booster can be put in a little amp cicuit like this:



Is it this simple, or am I missing something ?

[dano12]

Wow, that looks very promising.
Now I just wonder if this booster can be put in a little amp cicuit like this:



Is it this simple, or am I missing something ?

I've had stability issues trying exactly that type of schematic when the gain of the tube stage is at max and you max the gain on the 386. Starts to oscillate pretty bad. If you keep the gain lowered on the tube pre-amp, and adjust the 386 gain to taste, it should work. My breadboard tests with the 6111 and JRC386 were disappointing sound-wise.

[Krinor]

Dano, what tube are you using in that Tube Cricket of yours ?

[dano12]

Dano, what tube are you using in that Tube Cricket of yours ?

That's a 12AU7.

Let me dig up the schemo.


<edit: here ya go!>
http://www.beavisaudio.com/Projects/TubeCricket/TubeCricket_Final_2008.gif

[Krinor]

That's a 12AU7.

I was asuming that. 

Let me dig up the schemo.

Please do!

I'm thinking about maybe building a bridged thing with a tube in front. I'm not after the overdrive at all. I'd rather like a clean amp with a fixed gain (R2k2).

Edit:

Thanks! You've made me a very happy man!

[kurtlives]

Dano, what tube are you using in that Tube Cricket of yours ?

That's a 12AU7.

Let me dig up the schemo.


<edit: here ya go!>
http://www.beavisaudio.com/Projects/TubeCricket/TubeCricket_Final_2008.gif

When is the kit coming out? I have been waiting forver for it

[ambulancevoice]

is there any kind of socket for the 6111?

[bancika]

yeah, I saw one on eBay for 7$ a piece, those are very small 8 pin sockets. You can use 8 pin DIL IC socket for this too (see dano's post on the first page)

[Krinor]

Here's mine:



I built it in one of those gorgeous boxes from Pedalenclosures.
This is the point-to-point version. Did anyone else build from that layout ? Well now it's verified by me at least.
What a great little circuit. Thanks for posting this Dano!
I can see many applications for this one. It would probably be a nice building block for more complicated projects.
It is a bit "dark" sounding, meaning it has a lot of bass content (at least with my SG). How could this be fixed ?