You may have seen my "Murder One" amp thread: http://www.diystompboxes.com/smfforum/index.php?topic=73222.0
I thought I'd see how the same design philosophy works with a 12AU7. It does!
(http://i210.photobucket.com/albums/bb292/frequencycentral/ValvecasterHead.jpg)
That its awesome! and I am very jealous
Does this little design get loud enough for bedroom levels?
Quote from: liddokun on January 09, 2009, 04:38:22 PM
Does this little design get loud enough for bedroom levels?
Yes - I'm driving it at the moment with my stock Valvecaster and its cool. Clean its a little quiet at the moment, but i think a few more voltage increments using extra diode/cap stages after the MAX1044 wil bring it up to a nice level. I'm running it into a 12" 8 ohm speaker.
I've been thinking about building a valvy for a while but this has pushed it over the edge. Perhaps you could incorporate the valvy you are driving the amp with into the amp itself and then have it relay switched, or maybe that's defeating the simplicity factor of it?
Quote from: tux320 on January 09, 2009, 05:03:19 PM
I've been thinking about building a valvy for a while but this has pushed it over the edge. Perhaps you could incorporate the valvy you are driving the amp with into the amp itself and then have it relay switched, or maybe that's defeating the simplicity factor of it?
Yeah that has crossed my mind to use two dual triodes. I have a bunch of 6111 subminis - I'll have to try some ideas using a couple of them.
I would make the it push pull with a dual triode. Bit more output, kinda fun.
Then you would need another 12AX7 for the "pre-amp", got an extra triode now. Could do fun stuff with it.
Quote from: kurtlives on January 09, 2009, 05:29:30 PM
I would make the it push pull with a dual triode. Bit more output, kinda fun.
Then you would need another 12AX7 for the "pre-amp", got an extra triode now. Could do fun stuff with it.
...and it edges ever closer to being DougH's Firefly ;D
For the size and expense of all those caps, not to mention running the MAX over spec, I'd be tempted to just run two 12v transformers back-to-back and get a B+ of 240V... hmmm.
Quote from: andrew_k on January 09, 2009, 06:22:09 PM
For the size and expense of all those caps, not to mention running the MAX over spec, I'd be tempted to just run two 12v transformers back-to-back and get a B+ of 240V... hmmm.
Well, its only £1.00's worth of caps and diodes. But you are right. I'm running this from the MAX just because its on my breadboard already for the Murder One. The Murder One has a voltage limit of 90 volts due to that being the maximum voltage for the 5672 pentodes. That issue doesnt exist with 12AU7/6111, so maybe a 555 switch mode or the 12v transformers you suggest are the way to go. Quite frankly, I bought the fender reverb transformer just to mess about with, I'm amazed how easy good results have come.
Quote from: kurtlives on January 09, 2009, 05:29:30 PM
I would make the it push pull with a dual triode. Bit more output, kinda fun.
Then you would need another 12AX7 for the "pre-amp", got an extra triode now. Could do fun stuff with it.
I would need a centre tap transformer for push/pull right? I do have a small multi-tap 25v line transformer I could use for that.
$h!t!! Tubes are fun! Tube amps are double the fun.
Nice job! I think you have built the Blackheart Ant Killer for like 20% of the cost.
How does the output compare to a LM386 amp?
Quote from: Caferacernoc on January 10, 2009, 11:18:54 AM
Nice job! I think you have built the Blackheart Ant Killer for like 20% of the cost.
How does the output compare to a LM386 amp?
Thanks!
I've got a LM386 amp that I built but never boxed. I'll dig it out and do a comparision.
Well I just tried this idea with two 6111 submini dual triodes (I only have one 12AU7 in stock). It worked really well. I just have to study some similar topology tube amp schematics, as I'm easily getting nice overdrive, but I need to be able to clean it up.
Cool work frequencycentral. :icon_smile:
I was wondering how much mA the 12 volt supply must give.
Would 500mA be enough ?
Quote from: Salvatore on January 12, 2009, 08:52:16 AM
Cool work frequencycentral. :icon_smile:
I was wondering how much mA the 12 volt supply must give.
Would 500mA be enough ?
Thanks Salvatore!
Yes 500ma is enough. I'm using a 500ma filtered/regulated puwer supply.
A 12AU7 requires 150ma for the heater.
Two 6111, run with the heaters in series require 300ma for the heaters.
The plate ma requirement is minimal - I'm using the puny ma output of the MAX to provide that. If I remember rightly the MAX ma output is 20ma.
Rick I have seen this one and also the (in)famous MURDER ONE
Basically this is a Valvy with a trafo at the end, so it has one triode for the gain and one for the power (am I right?!)
The MURDER ONE can use a 12AU7 as the pre tube and a pentode as a power tube (am I right?!)
So I guess you could just have more gain with a murder one with a dual triode gain stage and a pentode at the end than this one, using one triode as pre and the other haf as a power tube (am I right?!)
Which of those solution is better in term of clean and distorted sound!?
Cool thread FC !
A tube amp that relies on a 'wimpy' enough chip that I think it qualifies as a non-lethal approach?
Less high tension...you know what high tension lines do in amps and how hard it can be to deal with that.
Pretty cool indeed !
Nice to have a milder amp. My smallest usable tube amp is my best buddy these days, the very obvious perfect choice until it's not loud enough to compete.
I feel like scaling down another few notches...might just be the next project !
My best new amp [built this week] is a friendly tube head, 12ax7 / 6v6 @204 on the plates. Small-watt has so many advantages over bigger [especially for producing a wide frequency response in 'idle air'], any more than that, IMO, is simply an obnoxious nuisance, with a stronger tendancy to be too powerful to control itself at low volumes, keeps wanting to jump up, doesn't respond right, tends to need comp. etc.
Once the PS and OT are figured out, getting a tube to do the trick isn't that difficult, about the same as wiring a couple transistors [well, of course the heater].
Quote from: Renegadrian on February 05, 2009, 08:36:11 PM
Basically this is a Valvy with a trafo at the end, so it has one triode for the gain and one for the power (am I right?!)
You are right, one triode is the preamp, one is the power amp.
Quote from: Renegadrian on February 05, 2009, 08:36:11 PM
The MURDER ONE can use a 12AU7 as the pre tube and a pentode as a power tube (am I right?!)
That's correct.
Quote from: Renegadrian on February 05, 2009, 08:36:11 PM
So I guess you could just have more gain with a murder one with a dual triode gain stage and a pentode at the end than this one, using one triode as pre and the other haf as a power tube (am I right?!)
Yes - I did quite a few different experiments as well as 'Valvecaster Head' and 'Murder One'. I also tried something similar to a Pepper Shredder with the fender reverb transformer at the end. I tried parallel triodes as the output stage too - not push/pull, but putting two triodes in parallel. Of all the ideas I tried, the final version of 'Murder One' seemed to me to be the loudest, and also the brightest.
Quote from: Renegadrian on February 05, 2009, 08:36:11 PM
Which of those solution is better in term of clean and distorted sound!?
At such relatively low voltage there is not much clean headroom. For a clean amp design more volts/headroom are needed than in 'Valvecaster Head' and 'Murder One'. My next amp experiment will hopefully get there, I'll be using two 7327 dual triodes for a push/pull amp with a Hammond 125A O/T, and a 555 based SMPS getting up to 100s of volts.
I think you should experiment a bit - breadboard a few ideas. If you want a dirty amp at low volume 'Murder One' would do the job, but it's clean sound is too quiet.
Quote from: petemoore on February 05, 2009, 11:20:03 PM
Cool thread FC !
A tube amp that relies on a 'wimpy' enough chip that I think it qualifies as a non-lethal approach?
Thanks Pete! That's the idea - a little tube amp that pedal builders can build safely without having to worry about lethal voltages.
Can't find both my breadboard and some free time... :icon_frown:
Can you suggest me a normal size pentode to sub the 5672?!
Quote from: Renegadrian on February 06, 2009, 08:14:59 PM
Can't find both my breadboard and some free time... :icon_frown:
Isn't that illegal???
Quote from: Renegadrian on February 06, 2009, 08:14:59 PM
Can you suggest me a normal size pentode to sub the 5672?!
5672 is the only pentode I've ever used. :-\ I know you have some pentodes in stock. So it really is a case of breadboarding/experimenting. The fact that the 5672 is directly heated (grid internally connected to the heater +ve) means any sub you used would have to account for this - you could have a look at other amp schematics for how to wire up grid 3.
You would also have to consider the sub tubes' output impedance - the 5672 output impedance is 20k so it's a close match to the transformer I used - I'm just getting started in how to work out impedance matching. Hammond do output transformers with many impedance options, the 125A for push/pull, the 125SE for single-ended for example.
Also, using a normal size pentode would mean you could work with higher voltages, as the 5672 is limited to ~67v in 'Murder One':
Quote from: frequencycentral on January 17, 2009, 09:24:36 AMIt would appear that although the maximum voltage for a 5672 is 90 volts it's not possible to apply a 90 volt plate voltage via a transformer (though ok via a resistor). Here's what Jasper Oosthoek over at the AX84 forum has to say about that: "If 90 volts is the maximum for the tubes, you cannot use it with a transformer (resistor is not a problem). As soon as you get a signal in the transformer its primary AC voltage will swing around B+. This means that if the AC voltage is 30 volts peak to peak, the anode voltage of the tube will swing between 75 and 105 volts. 60 volts on the anode might be a lot safer and will enable you to have 60 volts AC P2P (30 to 90 volts)".
There are lots of possibilities, but I think all require some expermenting!
Hi guys
frequency central that's cool!
I'm going to give this a try once the twincaster is finished.
I'll use the twincaster as the preamp.
I was wondering about the impedance rating of the matching transformer (fender reverb) it's 2800/1
The plate impedance of a 12au7 at 100 volts is 6250 ohms at 250 volts its 7700 ohms. Indicating that the impedance goes up as the plate voltage is increased.
The circuit that this transformer originally was taken from uses a plate voltage of 12 volts, I assume at 12 volts the plate impedance would be quite low.
I'm wondering if the higher plate voltage you are using would cause this matching transformer to no longer be a good impedance match for the 12au7 with a 60-100v plus plate voltage?
Glen
Quote from: biggy boy on February 09, 2009, 12:59:05 PM
Hi guys
frequency central that's cool!
I'm going to give this a try once the twincaster is finished.
I'll use the twincaster as the preamp.
I was wondering about the impedance rating of the matching transformer (fender reverb) it's 2800/1
The plate impedance of a 12au7 at 100 volts is 6250 ohms at 250 volts its 7700 ohms. Indicating that the impedance goes up as the plate voltage is increased.
The circuit that this transformer originally was taken from uses a plate voltage of 12 volts, I assume at 12 volts the plate impedance would be quite low.
I'm wondering if the higher plate voltage you are using would cause this matching transformer to no longer be a good impedance match for the 12au7 with a 60-100v plus plate voltage?
Glen
Yes you are right - there is probably a better match than the transformer I used. I got a Fender reverb transformer some weeks ago and just tried a few different ideas - I eventually used it to build my Murder One, the output impedance of a 5672 tube being 20K, so well matched. I'm not a very technical guy and am just getting my head around impedance issues - it takes someone like yourself to improve on my idea.
I came across this today: http://www.ax84.com/static/corepoweramps/2W_SE/AX84_2W_SE_Poweramp_Schematic.pdf which would suggest that the 12AU7 would work well with a 4K primary. So maybe the Hammond 125ASE would be a better match than the Fender reverb transformer as it has 2K5/5K/10K primary taps.
Quote from: frequencycentral on February 09, 2009, 01:18:50 PM
Quote from: biggy boy on February 09, 2009, 12:59:05 PM
Yes you are right - there is probably a better match than the transformer I used. I got a Fender reverb transformer some weeks ago and just tried a few different ideas - I eventually used it to build my Murder One, the output impedance of a 5672 tube being 20K, so well matched. I'm not a very technical guy and am just getting my head around impedance issues - it takes someone like yourself to improve on my idea.
I came across this today: http://www.ax84.com/static/corepoweramps/2W_SE/AX84_2W_SE_Poweramp_Schematic.pdf which would suggest that the 12AU7 would work well with a 4K primary. So maybe the Hammond 125ASE would be a better match than the Fender reverb transformer as it has 2K5/5K/10K primary taps.
Here's something this site shows you how to select and test any transformer to determin it's impedance and how to matchg it to you tubes. very good stuff.
http://www.radioremembered.org/outimp.htm
I'll have a look at that link when I get home from work! thanks. This tube stuff is alll new to me too. :icon_smile: I does help that I'm an electrician thou, makes it a bit easier to understand. LOL
Glen
Glen, are you a lefty too?!?
Quote from: Renegadrian on February 09, 2009, 06:26:28 PM
Glen, are you a lefty too?!?
Thread hijacked by southpaws alert!
Quote from: Renegadrian on February 09, 2009, 06:26:28 PM
Glen, are you a lefty too?!?
Sure am thats why I make my own guitars and basses!
(http://i107.photobucket.com/albums/m297/biggy-boy/pic1.jpg)
(http://i107.photobucket.com/albums/m297/biggy-boy/pic9.jpg)
(http://i107.photobucket.com/albums/m297/biggy-boy/pic15.jpg)
Quote from: frequencycentral on January 09, 2009, 04:20:07 PM
You may have seen my "Murder One" amp thread: http://www.diystompboxes.com/smfforum/index.php?topic=73222.0
I thought I'd see how the same design philosophy works with a 12AU7. It does!
(http://i210.photobucket.com/albums/bb292/frequencycentral/ValvecasterHead.jpg)
Still trying to put my head around tubes!
I notice there is no resistor on the Cathode terminal 3 and ground.
I guess this will give the circuit the maximum gain possible right?
So then the gain control is just in the preamp part?? in your case the Valvecaster preamp?
From what I have read so far I thought a resistor was needed on the cathode to create a situation were
the voltage to the cathode would be slightly higher then the grid voltage.
Sorry for so many questions. I'm not trying to question whether this circuit is right or not, I'm just trying to learn and understand how all this stuff works :icon_redface:
I'm a very curious person by nature. Man so much to learn. At least its Fun!!!
Thanks!
Glen
Hi Glen. This circuit was more a 'design for discussion' than a finished project. As you have already correctly suggested, it would work better (louder?) with a different transformer.
Quote from: biggy boy on February 10, 2009, 11:16:44 AM
I notice there is no resistor on the Cathode terminal 3 and ground.
I guess this will give the circuit the maximum gain possible right?
Correct, if you have a Valvecatser and turn up the Gain to maximum you are shorting the cathode to ground, so that triode is set up for maximum gain. With such a relatively low voltage amp clean sound are just not an option - too quiet.
Quote from: biggy boy on February 10, 2009, 11:16:44 AM
From what I have read so far I thought a resistor was needed on the cathode to create a situation were
the voltage to the cathode would be slightly higher then the grid voltage.
Many tubes designs use a low value resistor (say 1K) and a cap (say 1uf) between the cathode and ground. Thats probably better engineering than the Valvecaster's approach - but it works.
"By altering the values of the cathode resistor and cathode bypass cap, it is possible to roll off various degrees of bass with this triode stage." http://www.diystompboxes.com/pedals/tubedummy.html
Quote from: biggy boy on February 10, 2009, 11:16:44 AM
Sorry for so many questions. I'm not trying to question whether this circuit is right or not, I'm just trying to learn and understand how all this stuff works :icon_redface:
I'm a very curious person by nature. Man so much to learn. At least its Fun!!!
Keep asking the question - I ask a few too! And yes it's real good fun. :icon_biggrin:
That cathode gnd. is buried, i checked yesterday while adding a 220k to my 220k plate resistor to reduce gain on stage 1...
12aT7 though, and at 38vdc on the plate resistor.
I am about to dig that cathode ground wire up and put a little resistor in it, >470 I think. Then maybe fix gain starting 'low' 15k or something on stage 1 cathode, then through the 25k pot allowing cathode R adjustment between 15k and ~40k.
The way it gets played a lot now, it is nice 'meat'n potatoes' tone, I want to keep that, maybe make it to where it's even adjustable to less gainy !
Can anyone guide me to schematic of output stages of single ended tube amps that are paralleled or seriesed tube sharing the output load ?
I'm looking for examples...
12ax7: Anode current: 0.5 mA
12au7: Plate current: 10.5 mA
I have some reading to do...
I haven't been able to find the cathode current max rating on the 12ax7, perhaps a cathode follower could be designed to supply current and be of useful impedance to drive a speaker ?
Trying to get past the idea that a 12ax7 couldn't be made into an amp...thinking too hard about sketchy ideas of reducing plate resistance by making a parallel plate output...or something..well, that and having plenty of other things I know I should be thinking about.
Quote from: petemoore on February 10, 2009, 01:53:00 PM
I am about to dig that cathode ground wire up and put a little resistor in it, >470 I think. Then maybe fix gain starting 'low' 15k or something on stage 1 cathode, then through the 25k pot allowing cathode R adjustment between 15k and ~40k.
That's a good idea Pete - I find the 'thunk' when you turn the Valvecaster gain pot to max slighly annoying.
Some 12AU7 can 'whistle' when bypassed too if the cathode is dirctly connected to ground.
Quote from: frequencycentral on January 09, 2009, 04:20:07 PM
You may have seen my "Murder One" amp thread: http://www.diystompboxes.com/smfforum/index.php?topic=73222.0
I thought I'd see how the same design philosophy works with a 12AU7. It does!
(http://i210.photobucket.com/albums/bb292/frequencycentral/ValvecasterHead.jpg)
Hi
Rick just checking to see if you have added any more stages to your power supply?
If so how is the sound at the higher voltage.
I take it higher supply voltage equates to more headroom?
Glen
Quote from: biggy boy on February 14, 2009, 06:24:50 PM
Hi
Rick just checking to see if you have added any more stages to your power supply?
If so how is the sound at the higher voltage.
I take it higher supply voltage equates to more headroom?
Yes, I ended up with six stages, that's 12 caps and 12 diodes - that's what I used in Murder One. I have the same PS on my breadboard for some more experiments I'm doing. Each stage increases the volume, volts=volume with tubes. I stopped at ~70 volts as that's the limit for the 5672 tube in Murder One. 12AU7 can go higher though (check the data sheet) - so it would be worth exploring a switched mode power supply like this: http://www.ledsales.com.au/kits/nixie_supply.pdf
Quote from: frequencycentral on February 14, 2009, 07:31:13 PM
Quote from: biggy boy on February 14, 2009, 06:24:50 PM
Hi
Rick just checking to see if you have added any more stages to your power supply?
If so how is the sound at the higher voltage.
I take it higher supply voltage equates to more headroom?
Yes, I ended up with six stages, that's 12 caps and 12 diodes - that's what I used in Murder One. I have the same PS on my breadboard for some more experiments I'm doing. Each stage increases the volume, volts=volume with tubes. I stopped at ~70 volts as that's the limit for the 5672 tube in Murder One. 12AU7 can go higher though (check the data sheet) - so it would be worth exploring a switched mode power supply like this: http://www.ledsales.com.au/kits/nixie_supply.pdf
Ya I was looking at that power supply design looks good and fairly easy to make!
I'm thinking 100 volts plus would be cool to try out?
Glen
I just built a Nixie last week and so far, so good. Mine adjust's from 73 volts to 241 volts. I used a 10 turn 1K Helipot instead of the trimmer, so I could dial in precise voltages if need be.
I haven't tried it yet with a tube circuit. That will be the true test.
Quote from: Jered on February 15, 2009, 06:32:29 AM
I just built a Nixie last week and so far, so good. Mine adjust's from 73 volts to 241 volts. I used a 10 turn 1K Helipot instead of the trimmer, so I could dial in precise voltages if need be.
I haven't tried it yet with a tube circuit. That will be the true test.
Excellent - did you build the one I linked to above? If not can you post a schematic of what you built? How did you get the adjustment so wide? Will be interesting to see what you do with it.
Any idea how much milli amp load the nixie can handle?
Was wondering if it can handle two or three tubes a 12ax7 and one or two 6L6
Glen
Google found this:
http://www.desmith.net/NMdS/Electronics/NixiePSU.html
Great Page...
Mentions current draw of larger tubes is more than of smaller tubes...
Quote from: petemoore on February 15, 2009, 10:47:29 AM
Google found this:
http://www.desmith.net/NMdS/Electronics/NixiePSU.html
Great Page...
Mentions current draw of larger tubes is more than of smaller tubes...
There was a thread about that one recently: http://www.diystompboxes.com/smfforum/index.php?topic=74020.msg601045#msg601045
The noise generated and picked up by the audio circuit is one of the problems that concerened me as the inductors do emit a lot of RFI, you can use a shielded inductor but the efficiency will drop dramatically.
...so don't start with the PS inductors permanently fixed near signal paths?
Put the SP portion in a separate shielded containter?
Apparently the PS inductor works quite differently when shielding, perhaps a ground plane between Indy and the Signal path would keep inductor effeciency drop from being so dramatic and yet harvest fewer RFI problems in SP.
Put the PS inductors...'over there', then run a DC wire to the SP area ?
How much separation is necessary if...?
Experimental layouts will tell much more than the theories.
Perhaps some feedback from a sensor of RFI can test positions around the placed inductor [on a ground plane?] to sense what positions around the device have the highest and lowest outputs, or to find out it has omnidirectional characteristics to it's output.
I have not done much in the way of psu design before but its strange how you can get quite hooked into psu design. (always considered it a boring, secondary neccessity). I've always avoided circuits with inductors as they have been a mystery to me in the past, so this is also all about learning.
The above was typed before discovering how much of a problem the RFI into SP is, or what simple steps make satisfactory PS noise rejection to say pre-amp circuits.
This recent thread has surfaced some 'useful tips':
http://www.diystompboxes.com/smfforum/index.php?topic=74265.0
Quote from: frequencycentral on February 15, 2009, 06:42:30 AM
Quote from: Jered on February 15, 2009, 06:32:29 AM
I just built a Nixie last week and so far, so good. Mine adjust's from 73 volts to 241 volts. I used a 10 turn 1K Helipot instead of the trimmer, so I could dial in precise voltages if need be.
I haven't tried it yet with a tube circuit. That will be the true test.
Excellent - did you build the one I linked to above? If not can you post a schematic of what you built? How did you get the adjustment so wide? Will be interesting to see what you do with it.
Yes I built the one from your link. I have no idea why such a wide voltage range, but it does talk about the varied voltages in the write up.
I had also read the desmith article so I added a .1 ceramic disk at the output. I'm hoping for our simple analog builds that rfi interference won't be significant, but I still have not had the time to test it. Hopefully on my next day off.
Any news on these?
It saddens me that the small output transformers I have only go up to 8K primary impedance so I cannot try this out with my valvecaster... :( Also how much power would you estimate it produces as far as matching up a speaker to it goes...
Quote from: DUY1337GUITAR on September 06, 2009, 07:11:25 PM
Any news on these?
News? What news? It was an experiment. Never built one, moved onto other experiments. It works though - the more volts you give it the louder it gets.
I thought there was a 10mA limit on the 1044, wouldn't it be better with a 660? It has a 100mA max
The tubes don't draw much current, if you figure the plates are at half the supply which would be 30 volts, then the first stage draws 30/220,000 = 0.13ma and the second stage would draw 30/22,500 = 1.3ma so 10ma is more than enough.
It's the heaters in tubes that need a lot of current and that is supplied by the 12volt wallwart not the output of the voltage multiplier.
I was just interested. I'm probably gonna build one in the future. Make a nice looking head with the valvecaster (or maybe even a twincaster) and box a 12" speaker with it :)
Right now I need to finish my guitar project and buy a new main amp
Hey Doitle, If your 8k transformers are 8ohms out then just series up two 8ohm speakers for 16ohms and you'll double the primary impedance to 16k and if you use three 8ohm speakers in series you'll 24k primary impedance which is well close to 22.5k. Three sixes or eights could be quite nice.