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

[Ripthorn]

I wasn't implying having an extra stage for the power amp section, I was implying that a MOSFET phase inverter would give him an extra triode for the preamp section.  Though after reading that post again, I see where the confusion came in.  I was thinking that a single preamp gain stage wouldn't provide too much power to the power amp section.  I am thinking of using a MOSFET source follower for the tone stack on my next tube project.  That bought me an extra triode gain stage in the preamp that I am now using as a boost.  Keep us posted Rick.

[Boogdish]

Sorry, when you wrote "another triode stage for more output," I misconstrued what you were trying to say.  I should have read your other posts more carefully probably.

[Ripthorn]

Ok, Rick, quick question about this one.  Do you have any idea what kind of power output you are getting out of this?  I know the data sheet says each tube can do something like .95W or something, but I am curious what your experience has been.  Have you tried the power amp with some other preamp to see how much "umph" the power amp has?  I've got some 5672's for the low power section, but they seem like they would need a really high load resistance in push pull (like 32 or 40k) which the output transformer I am going to use can't do.

[frequencycentral]

Ok, Rick, quick question about this one.  Do you have any idea what kind of power output you are getting out of this?  I know the data sheet says each tube can do something like .95W or something, but I am curious what your experience has been.  Have you tried the power amp with some other preamp to see how much "umph" the power amp has?  I've got some 5672's for the low power section, but they seem like they would need a really high load resistance in push pull (like 32 or 40k) which the output transformer I am going to use can't do.

I'm not sure how to measure wattage output. I'm still running the Sub Zero at 80 volts. I'm waiting on a parts order to build the higher voltage switch mode power supply, which I'm hoping will get the power output where I want it to be. I just ordered a bunch of different subminis: 6112, 6397 and 5902. The 6112 have a gain of 70, compared to the 6111 I'm using now which have a gain of 20, so that should add some more power too, though I suspect it will just increase the available gain on the preamp and not the volume. The 6397 and 5902 are for another project. the 5902 are virtually non-existant on ebay, I should have taken you up on your offer - if you order anymore I'll definately have some, or let me know where you got them from.

[solderman]

The other design concept is to power it from a 12 volt wall wart. Murder One used a charge pump to get up to ~70 volts, Sub Zero is going to use a SMPS like this: http://www.ledsales.com.au/kits/nixie_supply.pdf

Hi Rick
I'm really interested if you got the Nixie working. I have tried without any luck. Mostly probably because i don't know where to find the correct diode and inductor no one seams to have the UF4004. I have tried different componets with fast switching high voltage diodes and different inductor coils. The only result as jet is smoke and tree fried IRF740 JFET:s

//Solderman

[Ripthorn]

Let me know how you like the 6112's.  The only thing there is that the only places I have found them are really expensive, like 10-15 USD per piece (and when I can get 6111's and 6021's for like 4 or 5 USD, it's hard to want to spend the extra, even if there is more gain).

[frequencycentral]

The other design concept is to power it from a 12 volt wall wart. Murder One used a charge pump to get up to ~70 volts, Sub Zero is going to use a SMPS like this: http://www.ledsales.com.au/kits/nixie_supply.pdf

Hi Rick
I'm really interested if you got the Nixie working. I have tried without any luck. Mostly probably because i don't know where to find the correct diode and inductor no one seams to have the UF4004. I have tried different componets with fast switching high voltage diodes and different inductor coils. The only result as jet is smoke and tree fried IRF740 JFET:s

//Solderman

Hi Anders,

I'm waiting for a parts order to build the SMPS. The correct diodes are available from Rapid in the UK, I've ordered more than I'll need, so PM me your address and I'll send you a couple. I hope I have ordered the right inductors.......they were from Rapid too. Again, I've ordered a few so I may have spare for you.

Let me know how you like the 6112's.  The only thing there is that the only places I have found them are really expensive, like 10-15 USD per piece (and when I can get 6111's and 6021's for like 4 or 5 USD, it's hard to want to spend the extra, even if there is more gain).

Hi Brian,

I think the 6112 will be cool........what about the 5902 you mentioned?

[Ripthorn]

The 5902's are on their way and will be part of the power section (I am going to have two power amps, one with 5672's and the other with 5902's and they will be switchable).  The 6112's interest me more for the preamp sections to get some of that uber gainy stuff going on (even though with five gain stages, even the 6021's get plenty of gain).  Are you planning to use the 6112's as the power amp or the preamp of this cool little thing you got going here?

[frequencycentral]

Are you planning to use the 6112's as the power amp or the preamp of this cool little thing you got going here?

I'm planning to use it for the preamp. I think it won't make much difference to the power amp part - I could be wrong. I'm also planning a couple Murder One varients using a 6112 pre, and 6397 or 5902 power amp- the extra gain of the 6112 should allow the addition of a tonestack.

[Ripthorn]

Mind if I ask where you got your 6112's?  They seem quite pricey everywhere I have looked.

[frequencycentral]

Mind if I ask where you got your 6112's?  They seem quite pricey everywhere I have looked.

Canadian ebayer if I recall.

[Renegadrian]

Guys, I feel it's like being part of a club - the TUBE club...
Everyone sharing its experiences to the others...That's unbelievable...

[Ripthorn]

I have noticed that there are a few of us that seem to be more dedicated to the tubes than the others.  I do dig how we basically all just meet up in the tube related threads and share ideas and such.

[MohiZ]

May I join in the tube club, then? 

I've read most of the valve wizard articles several times and I think I'm getting a basic understanding of the life of valves little by little. They are really good stuff!

I tried it first with 100 ohm cathode resistors on the output triodes, it's louder without. Is there any advantage to having them, what function should they perform? I'm still learning this stuff.

The cathode resistors are there to set the bias voltage in cathode biased configuration (to raise the cathode voltage higher than the grid voltage). The other option is fixed bias, where a negative bias voltage is applied to the grid. You kind of have a fixed bias of 0 volts in this configuration (which seems to work fine for these tubes).

After some quick calculations and looking at the 6111 graphs I came to the conclusion that it would, indeed, be louder without cathode resistors, and then you have pure class A operation. Maybe the only problem is that it creates slightly asymmetric distortion if driven, but that's not your intention. If you'd like class AB, then you should like to use, say, 220R to 3k3 cathode resistors. 680 ohms looks like a nice option. Class AB sounds a little different, with a more raw or dry sound to me. Usually class AB is used to get more power when class A would exceed the maximum dissipation of the tubes, and in these case it's not a problem.

(very roughly) Estimated RMS power w/o cathode resistor: 740mW, with around 680R cathode resistors 280mW so there is quite a difference. This is because of the low plate voltage and the tube in question. But according to the graphs, in this setup you're pretty close to getting the MOST clean headroom without the resistors. I calculated this for the 70 volt B+. With higher voltage supply, though, you'll have to add a cathode resistor to get this. Of course, which ever sounds better is the best way to go! 

EDIT: I had to revamp the whole post per the datasheet - for some reason the one from my source looked a lot different from the Tung-Sol one. I don't really even know what the point of this post is, I guess I just wanted to test my own knowledge and try to explain the cathode resistors 

[Jered]

  For the UF4004 diode just use a 1N4004. It worked for me.

The other design concept is to power it from a 12 volt wall wart. Murder One used a charge pump to get up to ~70 volts, Sub Zero is going to use a SMPS like this: http://www.ledsales.com.au/kits/nixie_supply.pdf

Hi Rick
I'm really interested if you got the Nixie working. I have tried without any luck. Mostly probably because i don't know where to find the correct diode and inductor no one seams to have the UF4004. I have tried different componets with fast switching high voltage diodes and different inductor coils. The only result as jet is smoke and tree fried IRF740 JFET:s

//Solderman

[Ripthorn]

May I join in the tube club, then? 

The club has open enrollment, so don't worry about it.

After reading your explanation of basically how to get class A and AB from a single power section, it makes me not so impressed at the amps that say you can have both class A and AB, just flick the switch.  It seems all you are doing is bypassing the cathode resistors on the power tubes.  Great, now I have to put that in my next amp too (in addition to two separate power amps, just more switches).  Anyway, good info.

Any chance of sound clips any time soon, Rick?

[Renegadrian]

May I join in the tube club, then? 

(cit.)
First rule of the tube club - there is no tube club! 
(/cit.)

[frequencycentral]

@ 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.

@ Jered - I'm surprised you got the SMPS working with 1n4004, but pleased for you. I'm curious as to the inductor you used. All my parts are on order - I'm hoping I ordered the right inductor - I hope to avoid flaming my breadboard.

@ Ripthorn - I wasn't going to do any soundclips until I've got it powered by the SMPS. At ~70v it's too quiet, I'm assuming that boosting the voltage to ~200v will put the volume where I want it to be.

@ The Tube Club - Have you guys seen this: http://jonanderson.mn.googlepages.com/5902 Weird really, I just got this idea into my head the other day to build an amp using a 6112 and a 5902, I ordered the tubes at the weekend, then I found that schematic today.

[Ripthorn]

I have seen that little amp on jon anderson's page.  It looks interesting, though I don't plan on a single ended amp immediately(wife is barely letting me do the one I'm working on right now).  I think I will use the nixie on the next project I do, though (probably single ended since I ordered 3 5902's and will only be using 2).

[solderman]

Hi Anders,

I'm waiting for a parts order to build the SMPS. The correct diodes are available from Rapid in the UK, I've ordered more than I'll need, so PM me your address and I'll send you a couple. I hope I have ordered the right inductors.......they were from Rapid too. Again, I've ordered a few so I may have spare for you.

Thanks Rick
Very kind of you but you don't have to since I will order some since I have a couple of other things i need BTW.  what was the part nr on the inductors you ordered??
Rapid, did not know of them I use Banzai or Musicding in Europe. Good prices since the $ and € has gone bananas to the SEK. The £ has not sky rocketed that much to the SEK.