"Sub Zero" Low Voltage Submini Tube Push/Pull Amplifier Project

[frequencycentral]

what was the part nr on the inductors you ordered??

This one: 88-1630  MIN RADIAL INDUCTOR 100UH RC

http://www.rapidonline.com/productinfo.aspx?&tier1=Electronic+Components&tier2=Inductors+And+Chokes&tier3=Leaded+Inductors&tier4=Low+current+radial+lead+inductors&moduleno=64730&catref=88-1630&kw=88-1630

I've never used an inductor before - fingers crossed it's the right one for the job.

[MohiZ]

@ Mohiz - Some very interesting comments and observations in your post. It's good that someone is prepared to do the math. I do read Valve Wizrad - but more for general concepts than the perplexing detail. My approach is on a more practical level: a little bit of knowledge, a breadboard, a good ear and a big wadge of curiosity and tenacity. I'm also curious as to how it wil sound when I get the voltage up higher, and what changes I will need to make.

I have a very technical mind, I've read the articles over and over again but am yet to try to actually build something of my own   Well, I do have a single triode thingy on the breadboard but I'm still failing to make it work the way I want it to.

[frequencycentral]

Let me know how you like the 6112's. 

I just received my batch of 6112's today. First impressions: they are a very different animal to 6111's, totally different sound, very full-on. Whereas with 6111's I try to get every ounce of available gain from them, the 6112's really need holding back some. Using the same resistor values I would use with 6111's, with the 6112's there's very noticable compression going on. I'm going to have to use lower value plate resistors and grid leak resistors to tame the gain a little. What fun!

On another note, I breadboarded the 6112 as a preamp driving a 5902 single ended amp. When using two 6111's (or 6112's, or 6021's) I usually put the two heaters in series like this:



This isn't possible to do with a 5902 and a 6111, as the 5902 draw 450ma and the 6111 draws 300ma. What would happen is that the 5902 would get ~4.25 volts and the 6111 would get ~7.75 volts. I scratched my head over this one for a while and came up with a workaround. Even then I wasn't convinced I was right, so I PM'ed R.G. and posted questions on a couple of tube amp forums. Both R.G. and Merlin (Valve Wizard) confirmed that my workaround works out. Here it is:



Basically, the 40 ohm / 2 watt resistor is in parallel with the 6111's 300ma heater. The voltage measured between the tubes is almost exactly half the supply voltage. The advantage of this arrangement is that the two tube's heaters draw together only 450ma. If they were powered normally from a 6.3 volt supply they would draw 750ma. It might not help anyone to know this, but it does mean that a single ended amp using a 6111 (or 6112 or 6021) and a 5902 can be run off a 12 volt / 500ma wallwart (and a charge pump / SMPS). Cool! 

[Ripthorn]

That is actually very good to know, because I bought a lot of three 5902's and am using two for a push pull pair in my current project, but plan to do a single ended one, so this will work great.  I have some 20 ohm 2W resistors that I can just put in series.  I also just got some 6112's, so I will see shortly what you mean about them (I hope, I want me some mean high gain!).  Thanks for all the great posts, Rick.

[frequencycentral]

Finally got all the parts to make the SMPS this week. I just finished breadboarding and testing it. I'm able to dial in voltages from 99 volts to 199 volts with the trimpot. 

No smoke, no fire , and a nice steady voltage. I'm just soak testing it before I use it to run anything, I going to run it on it's own for a few hours to see if it self destructs.

I've made a document with the schematic, pinouts for the semiconductors and the part number for the inductor I used:

[Ripthorn]

Nice work Rick, and nice to see that you get such a nice range of voltages.  What kind of current can that thing supply again?

I also got my 6112's, and I stuck them in to my existing design, only changing plate resistors to 100k.  The amount of gain didn't change too much (I made them the 3rd and 4th gain stage), but the volume dropped.  I think it might be just that the design was not really built around the 6112.  I think I may do something like a Trainwreck with the 6112's, or maybe something else, I will have to see.

I look forward to hearing the finished product.

[kurtlives]

^Brain there is a thread over at the Amp Garage about a sub-mini "Wreck". Might interest you 


That's a pretty cool PSU you got there Rick. Ill have to try it when I get some time.

Does it just use an old 555 timer? Also do you have any idea what other MOSFET can be used?

[frequencycentral]

Ok, after a while of running and still no smoke/fumes/flames I decided to hook it up to my Sub Zero, the two work perfectly together, I'm really pleased. I've got the clean volume I wanted. Under load the SPMS dropped from 195 volts to 185 volts. There's no sign of sag or compression. I'm going to try changing the tubes for 6112, with the 6111 preamp there's no chance of dirt, I think a 6112 pre would go from clean to dirty with the gain pot, just need to experiment a bit.

@ Brian: I'm not sure what ma it puts out. I don't really know how to test for that.

@ Chris: Yup it's just a cheapo standard 555. The IRF740 is a 400 volt N-channel MOSFET. I'm not sure what else you could sub for it.

[Ripthorn]

Hey Rick, the 6111 and 6112 data sheets say a max of 165V on the plates (I would assume higher is possible but may affect tube life) and just wondered if you knew and were giving this a go anyway, or what.  This does seem like a mighty nice way to power these things, and I may just have to try one out myself because I am not the biggest fan of transformers.  Though for the amount of tubes I will be running, I might need to build two, but that doesn't really bother me.  How quiet is it?  I suppose that depends a lot on the power supplied to it.  This has me thinking...

[frequencycentral]

Hey Rick, the 6111 and 6112 data sheets say a max of 165V on the plates (I would assume higher is possible but may affect tube life) and just wondered if you knew and were giving this a go anyway, or what.

Yeah, I should change them both for the 7327 I have, which have a much higher maximum voltage. I'm planning to see if it's possible to modify the SMPS to get more voltage. These 7327 are rare as hen's teeth though. Interestingly, just measuring the temperature of the tubes by touch, the power amp tube is much hotter than the preamp tube, really too hot to touch.

As for noise, if I put my ear right in the speaker I can hear some noise, but really nothing to worry about. If I remove the 330uf  cap (I think this cap should be a bit bigger) it gets noisy, and I can hear the high pitched whine of the oscillator, which is stange because the oscillator should be running at 45kHz. I might try changing the timing cap. The SMPS seems to draw a lot of current, judging by what else I can plug into my wallwart at the same time. I'll have to learn how to measure current draw sometime.

I think I'm going to eventually build one of these SMPS into a little box with a pot to vary the voltage instead of the trimmer, and add it to my prototyping setup. I have so many thing I need to try with this, like the 5902's I just got and the 6397's too.

[Ripthorn]

A quick way of doing current measurements is to take the red lead of your DMM and connect it to the positive power connection of your dc jack and then the black lead goes to the V in of your circuit (current is a series measurement whereas voltage is a parallel measurement).  I am really thinking I might need to try one of these.

[solderman]

Finally got all the parts to make the SMPS this week. I just finished breadboarding and testing it. I'm able to dial in voltages from 99 volts to 199 volts with the trimpot. 

No smoke, no fire , and a nice steady voltage. I'm just soak testing it before I use it to run anything, I going to run it on it's own for a few hours to see if it self destructs.

I've made a document with the schematic, pinouts for the semiconductors and the part number for the inductor I used:

LOL Good work. Then we know it works. I found why mine smoked. I had made a faulty connection and shortcut the FET. clumsy me. I have ordered new FET:s and the same inductor you used. Curious to here about the mA caus I'm planning to use  one 12Ax7 and one 12Au7 in the pre amp and one EL90 as a singel ended poweramp. The project name is PRAVDA as its loosely based on the Sovtek MIG 50. One of my favorite amps. The OT is a Fender 3,5W 8 Ohm reverb OT.
I plan to invoke a brake jack after the tone stack so I can use it as a pre amp/stompbox as well. The S1 is a relay controlled switch for switching between clean and dirty channel. With all this i might overload a Nixie supply but its worth a try.

Here is the UNTESTED schematics.

[Ripthorn]

Hey Solderman, that is a nice looking design.  I am curious about current draw too, but I think that your tubes might draw even more current than submini's, though it might be the other way, depends on plate resistance.  Anyway, my current tube project has the working name of "The Kitchen Sink" because it has clean and dirty channels, a booster, switchable and bypassable tone stacks, fat and presence controls, line out (complete with cab sims), line in and switchable power amps and switchable output impedance.  Now you don't have to wonder why it seems like I keep talking about it, but never finish it (I have ideas too quick to incorporate and finish the darn thing).

I must say Rick is quite the tube pioneer on this board, good work.

[frequencycentral]

As for noise, if I put my ear right in the speaker I can hear some noise, but really nothing to worry about. If I remove the 330uf  cap (I think this cap should be a bit bigger) it gets noisy, and I can hear the high pitched whine of the oscillator, which is stange because the oscillator should be running at 45kHz.

Oops - this was because I still have my MAX1044 charge pump running on the same breadboard. As soon as I disconnected power to the MAX the noise completely dissappeared. The SMPS oscillator and the MAX oscillator appeared to be interacting in a weird ring modulator sounding way. Something to bear in mind if you plan to run two of these in the same circuit.

I've now swapped out the 6111's for 7327's (which are equivalent but higher rated mil-spec), so they should cope with the high voltage better.

HIGH VOLTAGE WARNING: This SMPS is not as safe as the MAX charge pump. I managed to give my thumb a belt of high voltage, which kind of felt a bit worse than it does when you put a 9 volt battery to your tongue - I assume I'm not the only one who tests batteries this way? The electrons used in this circuit will steal your guitar, sleep with your girlfriend and leave you for dead. I was personally pronounced clinically dead to medical science fiction on three occasions while working on this circuit. Fortunately paramedics were on hand to revive my still twitching corpse. You may not be so lucky. If working on this circuit with the power engaged, keep both hands in your pockets. Always use a condom.

[biggy boy]

Rick
You are approaching the status of a low voltage/mini valve (tube) God
I sit here in amazement of your ability to create and produce so many great projects.
You have been keeping me very busy with them.
Keep it up, I'm learning so much!

Glen

[petemoore]

  What a great amp thread !
  Not to be pushy but I'd like it better if...
  I mean since you guys are building amps, if you have finished or working product...
  Does it growl when you kick it ?
  What type/size speaker is it able to power up.
  For any reviews on the sound of your project, could you include a basic outline of the tubes/project ?
  Interested...

[frequencycentral]

@ Glen: You flatter me sir! You are too kind, I'm just experimenting, having a lot of fun, and sharing my results. And yes, I hope to have a lot more to come this year, like submini tube phasers, wahs and envelope filters.

@ Pete: I run my little amps into the 12" / 8 ohm speaker of my Roland Bolt 60 watt vintage tube combo. I don't own a 4x12 cab, but would dearly love to get one, as the idea of sitting a tiny amp on top of one and rockin out would be so cool.

A few more observations on the Sub Zero:

I just did a side by side test against my Valve Junior (5 watt). At full power, the Sub Zero is about as loud as the VJ with its volume set to 3. I think that's pretty respectable.

I did try a 6112 as a preamp, I got similar result to Brian, the clean volume seemed to drop, although there was a lot of dirty gain available. I'm aiming for this to be a clean amp, if I want dirt with it I can use a pedal into it. So I'll leave the 6112 for another project.

I've been having a lot of fun overdriving the amp with an LPB (solid state!), it does sound great overdriven, though I've been enjoying the clean sound the most.

I've just done a perf layout for the SMPS if anyone is interested. While doing it, it struck me that the SMPS is not a very clearly drawn schematic on a few counts, not least because it is drawn right to left, which doesn't feel logical to me, so I'll redraw it and post it at some point.

[solderman]

If working on this circuit with the power engaged, keep both hands in your pockets. Always use a condom.[/b]

Hummmmmm...... I would rather use my hands instead of that part of my body with only a condom between Mr. me and 200V........

BTW found this with current experiments in it showing that 120+ mA is no bigger deal. That's promising cause that sort of gives the possibility in the range of 25W and that means that I might get away with 1-2W audiopower + losses in the circut.

http://www.desmith.net/NMdS/Electronics/NixiePSU.html

//Solderman   

[Ripthorn]

BTW found this with current experiments in it showing that 120+ mA is no bigger deal. That's promising cause that sort of gives the possibility in the range of 25W and that means that I might get away with 1-2W audiopower + losses in the circut.

Well, then it's official, I am going to have to build one of these.  That way I don't need another 12.6V/120V transformer (since the plates on my project only need a max of 80mA or so).  That should save money, real estate, weight and layout nightmares (for humming).

Rick, that is the best high voltage warning I've ever read, now I know where the name for your 6112 tube project came from...Darn SMPS.

[Ripthorn]

So Rick, do you have a layout for the Nixie?  Would be much appreciated.