I've got some of these MAX1771 to try, I know Mick (Ice-9) has already tried these and I've PM'ed with him to pick his brains, but I thought the topic deserved it's own thread, so here it is.
MAX1771 data sheet: http://datasheets.maxim-ic.com/en/ds/MAX1771.pdf
MAX1771 SMPS schematic: http://desmith.net/NMdS/Electronics/NixiePSU.html
I've redrawn the schematic, partly to go over the whole thing in my head, and partly to rationalise the schematic. I'm pretty sure it's correct, if someone would care to check it against the original that would be great.
(http://i210.photobucket.com/albums/bb292/frequencycentral/MAX1771SMPS.jpg)
I just breadboarded it without a result. :icon_cry: First mistake was that I misunderstood the value of RSENSE, which I read as 50R, it's actually 0.050R - that's tiny, and way lower than anything I have in stock. For the ultra fast recovery diode I'm using UF4004, for the MOSFET I've got IRF740 and IRF840 on hand. I've got a nice selection of inductors. I wonder where I'm going wrong (apart from the value of RSENSE). Should the diodes and MOSFET I have work with this? I also am at a loss to calculate the wattage needed for RSENSE - I need to relearn Ohm's law I guess.
So I've started this thread just to share the information publically, rather than just PM back and forth with Mick. Hopefully it'll also be useful to some other people too. Feel free to chip in anytime!
For high frequency switching power supplies, even more than for analog audio, *everything* matters. You may have some silly, trivial mistake, just like you or I could make on any circuit. Or it could be that the parasitic inductance and capacitance of the wire to the gate of the MOSFET is letting it oscillate at several hundred megahertz.
Have you read the datasheets on the control chip and MOSFET enough to have them substantially memorized?
Hi Rick ,
I see you got started on the Max1771 HV supply. The schematic checks out the same as the one i was starting from except there are 2 missing caps from pin 2 to ground (100n and 10uf) I think these need to be in your circuit.
The diode you are using will work just fine, infact its the same as i used UF4004 and the MOSFET is also the same IRF740.
Rsense is very important in getting the SMPS to work and you might want to double the resistance from .05 ohm to 0.1 ohm, this will halve the maximum current available. Rsense should be a 1watt resistor.
The 1M5 resistor must be a high voltage type as it will have nearly the full output voltage across it.
I hope this is some relevent info.
Quote from: R.G. on October 18, 2009, 03:15:03 PM
For high frequency switching power supplies, even more than for analog audio, *everything* matters. You may have some silly, trivial mistake, just like you or I could make on any circuit. Or it could be that the parasitic inductance and capacitance of the wire to the gate of the MOSFET is letting it oscillate at several hundred megahertz.
I've tried to keep jumping leads to a minimum, and been careful to not cross jumper close to each other. I'm aware that breadboards are not teh best places for SMPS's to live, though the 555 based SMPS I worked on last worked just fine on breadboard.
Quote from: R.G. on October 18, 2009, 03:15:03 PM
Have you read the datasheets on the control chip and MOSFET enough to have them substantially memorized?
:icon_redface:
Quote from: Ice-9 on October 18, 2009, 03:18:34 PM
The schematic checks out the same as the one i was starting from except there are 2 missing caps from pin 2 to ground (100n and 10uf) I think these need to be in your circuit.
I figured this is just filtering and ripple control, in parallel with the 100uf. My PS is pretty well filtered, but I'll add them to my schemo (and breadboard) when I get time though.
Quote from: Ice-9 on October 18, 2009, 03:18:34 PM
The diode you are using will work just fine, infact its the same as i used UF4004 and the MOSFET is also the same IRF740.
Thanks for confirming that Mick.
Quote from: Ice-9 on October 18, 2009, 03:18:34 PM
Rsense is very important in getting the SMPS to work and you might want to double the resistance from .05 ohm to 0.1 ohm, this will halve the maximum current available. Rsense should be a 1watt resistor.
Yeah - subbing in a 47R or 100R just isn't going to cut it is it?
I have no experience with that part so I'm not sure about this, but it looks like there is no compensation on the feedback network. Actually, I'm sure there is no compensation and this is risky business. If you're not careful, you'll accidentally create a fairly high frequency oscillator and/or increase output noise. Typically an extra pole is added to the feedback (in the form of a low-pass filter) to prevent excessive phase shift and potential instability. I would go with what the datasheet says and run the 1771 in bootstrap mode for the best performance. It doesn't cost much more (a few more passives) and makes for better regulation.
There are also some other little tricks that you can do to dramatically decrease the output noise. A snubber circuit across your MOSFET (series RC circuit from drain to source) is used to counteract the high frequency ringing that occurs from the leakage inductance of the inductor combined with the capacitance of the FET's drain. It'll probably be up in the 10-15 MHz range and while it's not necessarily audible, it does decrease the efficiency of the switcher by more than one would think. Another trick you can use is to have a Pi-network on the output. This looks like a cap to ground feeding a power choke feeding another cap to ground. The idea is that at DC frequencies, your caps and inductors look like open and short circuits, respectively. As you start getting higher in frequency, the caps and inductors start looking more and more reactive and shunt switching noise nicely.
I just got the parts in to start on my DIY switcher. Hopefully later in the week or next weekend I'll find time to play around with what I have. The IC used here (MAX1771) is too expensive IMO, I chose a part that was about $0.70 in single quantity from Mouser and they had thousands in stock. As much as I like Maxim's stuff, I usually avoid using their parts in designs that are meant to be inexpensive and/or built by many. The parts can be hard to find and when you do, you pay out the wazoo. Same goes for AD, they make fantastic products but they come at a premium price.
Hi Cliff,
I was wondering which chip you are using for your switcher?
The UC3842: http://www.st.com/stonline/books/pdf/docs/4299.pdf
Quote from: Cliff Schecht on October 18, 2009, 10:37:25 PM
The UC3842: http://www.st.com/stonline/books/pdf/docs/4299.pdf
I had originally considered using the UC3843 chip which is the same as used in the blackstar valve pedals, but as i had a max1771 already i tried with that. I think one of the advantages after reading the datasheets is that with the UC3843 the switching frequency can be set but with the max1771 it seems the swithcing frequency is controlled by the feedback to the chip itself and is constantly variable.
Nice looking chip Cliff. I can't wait to see your supply.
One thing I always intended to finish writing up but never got to was a power isolator. 9V in, 9V isolated out.
I've had several one-chip versions of this running, including one that was capacitively isolated, no inductive parts needed. That was fun. :icon_biggrin:
I think there's some commercial company that finally tumbled to this, supplying a "virtual battery" which is the same thing. It's just an isolator.
Easy enough to do once you think of it. Tricky to get it to work (a) reliably and (b) quietly. But a good candidate for postage-stamp PCBs.
http://www.interfacebus.com/Copper_Wire_AWG_SIze.html
Note the ohms per 1000ft. Take the wire size resistance divide by 1000. Lets take 38 gauge. 673 ohms per 1000 ft. 673/1000=.673 ohms per foot. or about .056 ohms an inch
Quote from: R.G. on October 19, 2009, 12:26:08 PM
One thing I always intended to finish writing up but never got to was a power isolator. 9V in, 9V isolated out.
I've had several one-chip versions of this running, including one that was capacitively isolated, no inductive parts needed. That was fun. :icon_biggrin:
I think there's some commercial company that finally tumbled to this, supplying a "virtual battery" which is the same thing. It's just an isolator.
Easy enough to do once you think of it. Tricky to get it to work (a) reliably and (b) quietly. But a good candidate for postage-stamp PCBs.
Wow, I can't believe that never crossed my mind before!
For the capacitively isolated version, what were the drawbacks in reliability? What chip did you design it off of?
To save you some trouble below is a very well documented MAX1771 SMSP + PCB:
http://desmith.net/NMdS/Electronics/NixiePSU.html
Quote from: MetalGuy on October 20, 2009, 04:22:17 PM
To save you some trouble below is a very well documented MAX1771 SMSP + PCB:
http://desmith.net/NMdS/Electronics/NixiePSU.html
That is the link refered to at the top of the page and is the schematic we have used as a starting point.
Could a variation of this power the tubes in the preamp stage(only the preamp!) of a dual rectifier? It uses 4 12ax7 tubes if i remember correctly.
Quote from: manis404 on October 20, 2009, 06:34:29 PM
Could a variation of this power the tubes in the preamp stage(only the preamp!) of a dual rectifier? It uses 4 12ax7 tubes if i remember correctly.
My interest in SMPS's is in powering small amplifiers with them, I've already had success with a similar 555 based SMPS: http://www.diystompboxes.com/smfforum/index.php?topic=78302.0
So, yeah - that's certainly possible, providing the SMPS will provide enough current for 8 triodes. But each 12AX7 plate is something just above 1ma IIR, so I'd say yes, as this SMPS should be able to deliver 50ma.
QuoteThat is the link refered to at the top of the page and is the schematic we have used as a starting point.
I noticed that now.
Quote...so I'd say yes, as this SMPS should be able to deliver 50ma.
The article says that it can do up to 100mA.
Hm, interesting stuff.
(Writes down this trivial comment for future topic notivication. ;D)
Well, I can't justify making an order to Banzai for just a couple of 0R050 and 0R1 1 watt resistors, so this'll have to wait for a little while.....
@ Mick (Ice-9): does the IRF740 in yours get very hot? I ask because the IRF740 I used in my 555 SMPS does get hot and needs heatsinking, and the site the schematic is from states "At no time did any component get hot - the FET was always cool to the touch, and the inductor warmed up only under heavy loads, but never got hot."
Quote from: frequencycentral on October 21, 2009, 03:33:23 PM
Well, I can't justify making an order to Banzai for just a couple of 0R050 and 0R1 1 watt resistors, so this'll have to wait for a little while.....
@ Mick (Ice-9): does the IRF740 in yours get very hot? I ask because the IRF740 I used in my 555 SMPS does get hot and needs heatsinking, and the site the schematic is from states "At no time did any component get hot - the FET was always cool to the touch, and the inductor warmed up only under heavy loads, but never got hot."
Rick, if you want I can mail you a few 0.1 Ohm 3 Watt SMD resistors to play around with..
QuoteWell, I can't justify making an order to Banzai for just a couple of 0R050 and 0R1 1 watt resistors, so this'll have to wait for a little while.....
Farnell have all the parts for this project.
Quote from: frequencycentral on October 21, 2009, 03:33:23 PM
Well, I can't justify making an order to Banzai for just a couple of 0R050 and 0R1 1 watt resistors, so this'll have to wait for a little while.....
@ Mick (Ice-9): does the IRF740 in yours get very hot? I ask because the IRF740 I used in my 555 SMPS does get hot and needs heatsinking, and the site the schematic is from states "At no time did any component get hot - the FET was always cool to the touch, and the inductor warmed up only under heavy loads, but never got hot."
The mosfet (IRF740) doesnt even get warm at all. I have no heatsink on it either.
I'll have a look see if i have some spare 0r05 resistors if you need any. Yup just looked i have some SMD ones let me know if you want a couple.
Rick do you not have a RS components anywhere near where you live, I use mine regular for anything, from single components to tools, if there not in stock when i go down they get them there for next morning no postage costs. There not really that expensive either (only expensive on certain items)
It occured to me that the MAX1771 smps schematic lacks the snubber that the 555 smps includes, it's the 2.2K resistor in series with the 100pF cap between the drain of the IRF740 and ground. According to Cliff:
Quote from: Cliff Schecht on November 04, 2009, 12:53:44 PM
It looks like a snubber circuit to me which goes in parallel with the FET's drain and source terminals. Or in this case, because you've got voltage-mode control, it goes from the drain to ground. These can increase efficiency in the FET by 20-30%, sometimes more with excessively ringing circuits!
As these SMPS's were designed primarily for use with nixie tubes and not audio tubes, maybe the necessary filtering isn't there and needs to be added?
The filtering is really just there to kill the ringing that occurs in every (unsnubbed) boost supply. I'm sure that if you look at the drain of the FET on a scope you'll see the ringing I'm talking about. Fortunately it occurs at a frequency much higher than that of the actual switching frequency and is (almost) always completely inaudibe. But it does decrease efficiency and can reduce the life span of some of the critical components. The FET, diode and output caps all can suffer from excessive ringing whose P-P voltage actually goes above the rated value of the part. This overvoltaging only occurs for fractions of a second but it still can do its damage over time.
Snubber circuits eliminate this ringing like a champ (also cuts down P-P output noise!) but still have a caveat in the form of power dissipation. Some snubber circuits require a fairly high wattage resistor because of the amount of energy that the capacitor is absorbing can become quite substantial if the frequency is low enough. There are also different types of snubber circuits depending on where you are trying to eliminate ringing. Do some googling for snubber circuit design and see what you find there, I don't know that guys design well enough to say if it warrants one.
Rick and Cliff... any new developments on the SMPS designs?
Rob
Time and lack of effort have been killing me as of late. I've just been in "go" mode for so long now that I'm trying to use my free-time to relax a bit instead of getting home from school and building stuff. I've spent so long building stuff for my guitar playing needs that I wasn't even really playing guitar! Anywho, I will look into my design again later and see if I can't get my design retested and finished.
Still not onto it yet. But I just sold my Superfly (submini Firefly) amp, I'll be building another, so it's a good opportunity to test the MAX1771 SMPS......
From what I can tell the MAX1771 design is a good one. I haven't tried it or done any testing on it or anything though. Knowing what I know now, I might change my design to be of the same style (voltage-mode controller with voltage feedforward).
When testing an SMPS like this how should you measure output correctly?
Simply meter to + and -? or do you need a load across the output?
Rob
Thought of another question for the Guru's of HV. Is there a reason these designs are on small separate PCB's? Is there an issue with combining an SMPS with another circuit on the same board
Quote from: robmdall on February 02, 2010, 05:51:27 AM
When testing an SMPS like this how should you measure output correctly?
Simply meter to + and -? or do you need a load across the output?
Rob
Thought of another question for the Guru's of HV. Is there a reason these designs are on small separate PCB's? Is there an issue with combining an SMPS with another circuit on the same board
You can measure the output without load to test it's working, but be aware that it will drop significantly under load.
Read enough info on SMPS design and layout and it will totally put you off building one on it's own, let alone on the same board as the circuit to be powered! ie issues surrounding ground planes, using 'just the right parts' etc. My approach is more ghetto, if it works it works and f##k the science. Here's a 555 SMPS on the same board as a submini tube amp:
(http://i210.photobucket.com/albums/bb292/frequencycentral/100_0111.jpg)
Rick that board is so cool, far from Ghetto... Although I like Ghetto. Yeah, you are correct, the freaking more I research the SMPS, the more difficult it becomes in my mind. Your design (in the beginning of this thread) is actually very straight forward. I guess the best thing to do is bite the bullet and build it. Thanks for the reassurance.
Hi - I'm the author of that MAX1771 design - its been recently updated to use more readily available components - the original ones specified were pre-RoHS. The PCB has also been changed slightly. http://desmith.net/NMdS/Electronics/NixiePSU.html (http://desmith.net/NMdS/Electronics/NixiePSU.html)
I can say that I've used it for small headphone amps etc. and there is at least one US-based guitar effects manufacturer who is also using it. Also, over on diyaudio, several people have also used it with great success.
The design switches at about 55-60kHz using the components specified - a nice ceramic output filter and GOOD filtering on the input side (to prevent those switching transients appearing elsewhere in the circuitry) makes it very usable for small tube designs. I tend to enclose/screen mine in a small box made from bits of FR4 PCB soldered together - a common radio ham trick.
There is no snubber for the FET as its completely unnecessary in this design - the MAX 1771 internal driver is explicitly designed for this job - a 555's is most certainly NOT. Further, no feed-forward capacitor is needed on the top of the feedback network. The design as it stands is very stable and there are many 100s of these running happily. Several of the commercial designs being sold on eBay and elsewhere are direct lifts.
What IS very important is to take note of my comments in the design notes re: component choice and layout. These are very very important. The MAX1771 is a bit of a Ferrari in the SMPS world - it's very efficient but can be temperamental - there is definite method in my madness!
Quote from: frequencycentral on February 02, 2010, 12:34:03 PM
Quote from: robmdall on February 02, 2010, 05:51:27 AM
When testing an SMPS like this how should you measure output correctly?
Simply meter to + and -? or do you need a load across the output?
Rob
Thought of another question for the Guru's of HV. Is there a reason these designs are on small separate PCB's? Is there an issue with combining an SMPS with another circuit on the same board
You can measure the output without load to test it's working, but be aware that it will drop significantly under load.
Read enough info on SMPS design and layout and it will totally put you off building one on it's own, let alone on the same board as the circuit to be powered! ie issues surrounding ground planes, using 'just the right parts' etc. My approach is more ghetto, if it works it works and f##k the science. Here's a 555 SMPS on the same board as a submini tube amp:
Small point - a 555-based SMPS will always be very inefficient - typically 70% at very best, more typically around the 55% mark in my experience.
Also, the comment about sagging under load is simply wrong, so long as you stay within the design parameters of the supply and your design is regulated - your 555 SMPS may well not be regulated - there are many regulated 555 designs out there (it only takes a few extra components - see the files section of the Yahoo neonixie-l group for several examples). The MAX1771 design IS regulated and delivers up to 100mA quite happily at 87% or so and 180VDC. I tested the loading by using non-inductive and then wirewound Al load resistors - its all documented on the original design page.
The MAX1771 design has been built on the same boards as the rest of the circuitry by many users - you just have to be a bit more careful. If you are happy with an unregulated inefficient design, that's fine, but it really is not that difficult to build an MAX 1771 design - I've built loads of different SMPS designs, and if you obey the simple rules, its not a problem.
It all comes down to what you want. If you want an efficient, quiet, stable, predicable & small design then use a specialised SMPS chip (like the MAX1771). If you just want to get something working from bits you might have lying around, then use a 555 design - the two are apples & pears. But don't kid yourself the interference & other general issues about using SMPSs in audio kit will magically go away if you use a 555 - all the the problems will still be there.
Thanks for the update Nickds1, i had originally used the older circuit from the site you mention and included the SMPS into PCB that has the rest of the circuit as well. I will check out the newer version you mention.
Nick, welcome to DIYStompboxes and thank you for your posts regarding the MAX1771 design! I've worked on similar switchers that were inspired by this design, albeit I went with current-mode control and a Unitrode controller as I find Maxim to be too expensive and usually too specialized. Then again, I didn't know until recently that Maxim has such an extensive power management portfolio, so I guess my spite for Maxim was more out of ignorance than anything.
My real goal in designing a miniature HV switcher was to meet or beat the capabilities of your switcher. I did manage to do so, making a slightly smaller board that could put out a little more power (about 40W at 250V) but I'm still yet to be able to finish the "production" board design because of school and work and what not. But thanks again for the inspiration, I soon hope to be "competing" with you in the DIY community with my HV design :).
Also, I think I've made similar comments about the 555 timer based supplies. While they aren't complete crap, nothing beats a well designed switcher!
Finally got this on the breadboard. Not having any 10K trimmers in stock, I had to sub in a 1k trimmer and fiddle with the voltage divider values to get it to work. I'm using 180k/1k trimmer/1k, and am able to dial in voltage between 159v and 317v. At one point when fiddling with the voltage divider values I mis-read a resistor value and got over 500v, which let a little of the magic smoke out........Anyway, I've had it running at a steady 250v without load for the last hour or so. There is no heat being generated anywhere - very cool (in both senses of the word) compared to 555 SMPS's. Now to build an amp around it............
(http://i210.photobucket.com/albums/bb292/frequencycentral/000_0035.jpg)
Guess what going on the rest of the board?
(http://i210.photobucket.com/albums/bb292/frequencycentral/000_0036.jpg)
QuoteAt one point when fiddling with the voltage divider values I mis-read a resistor value and got over 500v, which let a little of the magic smoke out.
What fried? I've got a need to get up into the 400-450v range for some high gain tube preamps, and I think I know where to start, but knowing what failed on your build would be valuable information.
Quote from: defaced on April 08, 2010, 10:20:22 AM
QuoteAt one point when fiddling with the voltage divider values I mis-read a resistor value and got over 500v, which let a little of the magic smoke out.
What fried? I've got a need to get up into the 400-450v range for some high gain tube preamps, and I think I know where to start, but knowing what failed on your build would be valuable information.
I ended up using a 220k resistor/1k trimmer/1k resistor arrangement, I mistook a 22k for a 220k.......now that let the genie out of the bottle - I now have a blackened 22k resistor. :o
You are actually quite lucky it worked on a proto board - MAX1771s are pretty sensitive to stray capacitance and you may have a few unexpected high frequency artifacts in there - if you have a 'scope, I'd check it carefully... (a good start would be to check the efficiency - it should be around 85% for a reasonable layout...)
Cheers
Nick
I found the circuit to be very unstable on breadboard, a hovering hand above it would cause noise, and touching the MOSFET made the voltage drop considerably. One I moved it onto perf it really settled down, it doesn't appear to mind the proximity of the hovering hand, or even touching the safe parts of the circuit. I'm using to to run a 12AX7 / 12AU7 SE amp into a Hammond 1750A. I'm getting a steady 240v out of it under load. The amp itself is on breadboard. The only real artefacts I've had have been solved by addressing the gain structure and power filtering of the amp itself.
TBH, before I built it onto perf I expected it would be pretty unstable, and had thought about making the unused pads into a ground plane. It really does seem very stable though, I've had the amp running for many hour continuously, just to soak test it. I'm a happy moo cow!
So this design will deliver a solid 50ma at 240 volts under a load? can it deliver more than 50ma?
Switching power supplies are a mistery to me, I studied them a little and was totally turned off by it, and specially because the pcb layout requirements. I wanted a HV power supply and I stumbled across the Nixie power supply, I downloaded the eagle files, and I was about to send it out to be made, but can't find the specified inductor, I picked a different one, but I am going to have to change the PCB footprint.
But now I am curious about the 555 design, didn't even occur to me that the 555 could be used for something like this. And it worked on a perf board, was this luck or this circuit not as sensitive as the other one?
Would it be possible to get up to 300V of either circuit?
@frecuencycentral
Sorry I misread, I thought the MAX1771 didn't work on a perfboard. You made it work, but your perfboard work is really impresive. Might not work if I do it.
I really dig this design now and may go a similar route with my future endeavors. I'm convinced that the current-mode boost topology I chose for my first few designs was both unnecessarily complicated and an antiquated design. A modern voltage-mode controller with voltage feedforward is just as safe/stable as a current-mode controller but uses less parts.
What I really want to start working on is a dynamic sag control that would allow you to simply flip a switch/turn a pot to increase/decrease the transient response (may take more trickery to get a tube rec/cap type response though). You could even use an envelope follower to add truly dynamic control of the power supply. I know others have done this, but I don't think it's been done on the scale of an entire tube amplifier before (at least intentionally!). I know Andrew did a sag emulator dealy once, but that's about the extent of what I've seen and I think that was for pedals, not tube gear.
mostly greek to me but are you talking about controlling the voltage from a knob? That would rule. would it change bias etc though?
Well, no that's not what I'm talking about. But there is a knob to adjust the voltage as necessary. Some resistors and a pot could be used to fine tune the B+ or power scale the amp. This doesn't affect fixed bias circuits because it doesn't generate a fixed bias (this requires a separate circuit).
What I'm talking about is something that allows you to adjust the response time of the power supply. A tube rectifier/capacitor combo doesn't react instantly to changes in power needs, there is a delay. This causes the output voltage to sag for a bit, adding some distortion and compression to the signal. Most people don't like this, but we as guitar players do. What I want to do is accurately emulate this in a DC-DC converter and actually make the amount of sag adjustable. I have a few ideas for either switching in sag or dialing it in, but this is all just speculative still (as is my mini HV SMPS :D).
ok now i get it. I was not aware of that to be honest and i always wondered why a tube rectifier was considered to better or worse than solid state.....Thanks for the clue!
Help Rick, Cliff, Nick, somebody,
Hey guys I have the SMPS on pcb and followed Nicks layout comments. I have the proper voltages but am getting lots of ringing. Any ideas?
Thanks
Bad ringing on the output? This shouldn't be a problem unless you have excess parasitics somewhere (long, skinny traces for the power routes for example). What inductor did you use? If the Q is too high at your frequency (well frequencies since this isn't a fixed PWM SMPS), you could be resonating the crap out of the inductor (a small series resistance can drop the Q). I doubt this is the problem though. It could also be a bad solder joint. I can guess all day long but posting some scope shots of the ringing would really help out.
Also remember that tacking on a scope lead adds a lot of extra parasitics and could cause ringing that isn't really there.
Not so technical as Cliff's reply, but when I was doing mine there was an optimum 'sweet spot' of the trim pot where I got clean output, not neccesarily the highest voltage but the best compromise between decent voltage and no noise.
Ok, that helps. I was looking for a clean signal all the time. How sweet is the sweet spot? And you are getting it from the pictured layout? I talked to Nick de Smith and he suggested these
http://uk.farnell.com/murata/bnx002-01/filter-dc-power-10a/dp/9526943?Ntt=bnx002
Little rcl filters. I don't know if I have enough room to use them but you might try them. He also pointed out how important it is use a two sided board to separate the ground plane, mmmmmkay,
Back to the drawing board. Thanks, that does really help.
Well it's pretty 'sweet'. I slightly tweaked the schematic to work with a 1k trimmer instead of 10k, so I used different resistor ratios in the voltage divider to get the trimmer to work over the most useful range.
Something else to bear in mind is that the ringing you are hearing may not be from the SMPS, but from the (tube) audio circuit itself. If I try real hard I can get either or both of motorboating (low frequency) and squealing (high frequency) from a high voltage tube circuit. So you may want to look at the topology of your audio, ie rein back the gain between stages by looking at increasing cathode resistor values and/or grid stopper values, even by removing cathode bypass caps. You might also want to seperate the B+ feeding the different triodes into B1, B2 etc in the classic tube amp way of a voltage drop resistor and electro cap to ground. This should help a lot. Especially if you have in-phase triodes (1 and 3, or 2 and 4) sharing the same B+.
Getting HV tube audio to work well with SMPS is a big juggling act, you change one thing then you have to compensate somewhere else. There are many possible combinations that won't work well, it's a case of making small changes and noting down what differences there are until you blindly stumble upon (if you're like me :icon_biggrin: ) the specific set of compromises that equates to the the optimal formula. Suspect everything - don't blame the SMPS until you're satified that it's not the audio.
This is really true when the SMPS is designed as a variable one. The requisite frequency compensation is setup and optimized for one DC level and so shifting around the feedback resistors will have a direct effect on stability. The best results will be achieved by overdesigning the power supply for your needs (keeps the heat down) and not making it uber-adjustable. Knowing what your needs are and designing to these specifications will almost always lead to better results, especially with touchy SMPS's. Perhaps I'll eventually get around to designing something for the forum..
Thanks for the help everyone. I will go back to basics and start again.
Hey Rick, I like the tattoo joke!
I will let you all know how I am coming along.
Cheers,
Chris
Is anyone making these for sale? I would love to just buy one with an instruction sheet. Just wondering. High voltage is intimidating already. Making this seems a little more intimidating.
There are some nixie power supplies on eBay that are similar to this circuit. I haven't used them yet, but their price seems very reasonable.
If your refering to the 1363, 1364 from taylor electronics yeah ive used them. They are cool but it seems like unless you have them loaded up just right they whine like a mother. This design also is higher voltage and delivers more ma from 9 volts.Thanks though, always nice to get pointed in the right direction..
First post, to a bit older thread & not really about a stompbox but somewhat relevant I think. Since I got something out of this thread thought I'd post some info from some tests of mine related to tube hybrid headphone amps.
Not a real designer, more of an assembler, I did the (mostly reference) implementation of the heater SMPS in Cavalli Audio's CTH. SMPS heater was the only option to meet our stated goals for the CTH & its working well.
It got me thinking why not investigate boost/HV SMPS for B+. Could not find a lot of info around about this so figured I'd play around with it.
Anyway attached is a pic of something I've got mostly working, actively loaded grounded cathode / IRF510 SE w/all power from a 12.6v 1.5A DC supply.
I say mostly because as zambo relates, the taylor 1363/4 is not appropriate for the task (high freq whine). Almost passable @ 200v only if heavily loading it (Rk / Rak @ 300R) so its switching freq rose to the upper limit of hearing & shielded the unit (use of a shielded inductor would have helped). E.g. my teenage son can barely perceive the HV freq in headphone output with no signal source. Play something through it & its pretty good. BTW made some changes after this pic.
(http://i2.photobucket.com/albums/y33/pbcubed/smhv_test.jpg)
Well I decided to order the built ogi lumen implementation of Nick's MAX1771 project to see if that's up to this task.... But @ $65 USD its a bit pricey.
QuoteI say mostly because as zambo relates, the taylor 1363/4 is not appropriate for the task (high freq whine). Almost passable @ 200v only if heavily loading it (Rk / Rak @ 300R) so its switching freq rose to the upper limit of hearing & shielded the unit (use of a shielded inductor would have helped). E.g. my teenage son can barely perceive the HV freq in headphone output with no signal source.
Hmm. That kinda sucks, I bought two of these finally hoping to do tube preamps with them, but completely forgot I recommended these and to check back on the thread. So... and I'm pretty sure I know the answer, but the whine, is that coming from the SMPS unit itself or is it hash in the DC power or both? I'm pretty sure the answer will be both but I figured I'd ask.
> but completely forgot I recommended these
Heh, I didn't see that in this thread. Anyway they could have been a nice, cheap solution so it was worth a try. There are not that many off-the-shelf solutions that provide at least 200V, besides googling here's a nice resource:
http://www.tayloredge.com/storefront/SmartNixie/PSU/comparison.html (http://www.tayloredge.com/storefront/SmartNixie/PSU/comparison.html)
> is that coming from the SMPS unit itself or is it hash in the DC power or both?
I think its coming from both (would have to scope around to confirm)... I cut, bent & installed a little sheet metal box over the switcher (in lower-left of pic above) and seemed to reduce the audio level of the freq in the amp's output to "barely there" w/no signal & not perceivable with any signal (YMMV). So think some of this is RFI and might be reduced though use of a shielded inductor... BTW I'll be ordering the shielded one for Nick's/ogi's solution if I have any issues with that piece.
But think some of this is also coming direct through B+. Note I'm using dual CTH cap multiplier filters for B+ (the raised protoboard strip along left in pic, schem on cavalliaudio).
I asked TE what chip they are using on these 1363/4 to research this a bit (as the #s on mine were rubbed off/not legible), but haven't heard back. Again the only chance to use these for audio seems to load them up so they crank their freq up (e.g. 100k across output, tube draw, lower the input V) & shield them, but it seems to me to plateau at the very top edge of audible range.
Will be curious what you find if you play w/them. Please let me know if you can read the #s on the switcher. At least they are great for testing / proof of concept, enough so I'm pursuing the MAX1771 solution, and we can always build a Nixie clock w/'em someday:)
I grabbed my camera and took two pictures of the board with different lighting angles. It looks like the chip in the upper right is made by STMicroelectronics, but searching for their website and Google gave me nothing. The other chip 8 pin chip, to the left of the big one in the MS8 package, is made by Linear Technologies, part number LT1619, here's the data sheet: http://cds.linear.com/docs/Datasheet/1619fa.pdf (http://cds.linear.com/docs/Datasheet/1619fa.pdf). I'm thinking that the STMicro chip might be an MCU...???
The images are about 1M each in size.
http://img690.imageshack.us/img690/2945/smps2.jpg (http://img690.imageshack.us/img690/2945/smps2.jpg)
http://img841.imageshack.us/img841/2382/smps1.jpg (http://img841.imageshack.us/img841/2382/smps1.jpg)
Nice pictures, thanks.
Now I have to say that the high frequency "whine" / tone /oscillation I hear from this SMPS in my application is a mystery.
AFAIK "modern" switchers operate @ freqs well above 20kHz/audible range. And yes, it is emanating from the SMPS & not somewhere else in the circuit.
That LT doc/chip you found appears to operate @ 200kHz+. So maybe what I'm hearing is not switching frequency but something else (e.g. ringing / oscillation) as IIRC putting a finger/pressing on the switcher's inductor reduces the sound. Other posters in this thread are much more knowledgeable about this than I, but maybe I'll fool w/this switcher a bit more & see what I find. At least until the MAX1771 arrives:)
Perhaps this little $13 #1363 HV supply design is just not that robust/stable, at least not with what I'm asking it to do.
Will be curious what you find if/when you give that 1363 a go in a circuit.
Edit: Well just found a lot of good (but discouraging) info WRT SMPSs & audio in the "Do SMPS have a home at high end audio?" & other threads over @ diyaudio. But everyone chooses their compromises so I may keep at it:)
QuoteWill be curious what you find if/when you give that 1363 a go in a circuit.
Me too. I was originally hoping to run both of them from a single supply and stack the outputs for 400v circuits (most high gain tube circuits are 4 stages + CF and start upwards to 400v). Then I discovered that the grounds for the input voltage are shared with the output, which means I need either two power transformers or a transformer with two secondaries. Not the end of the world, but it's not what I have on hand. But, yea, anyway, I'll post whatever I find when I find it. This will be a nice project once I get my scope up and running.
so i am not really sure but would it help to go with more of a traditional resistor/cap/res/cap type of power supply fed by a 1363?
Quote from: zambo on January 19, 2011, 09:18:16 PM
so i am not really sure but would it help to go with more of a traditional resistor/cap/res/cap type of power supply fed by a 1363?
Having communicated w/someone knowing a lot more than I about this, yes something like a RC or LC PI filter @
100kHz 40kHz or so (?) would suppress most modern switcher's freq in output/B+.
But don't think that's the problem we are experiencing (e.g. the coil squeal/oscillation) w/the 136Xs. Again my total guess is its a not the most robust/stable implementation, e.g. maybe its got a "sweet spot" where it doesn't squeal/oscillate but who knows where that is.
And that electromechanical(?) emanation did seems to pollute my little test amp.
Maybe someone else will get somewhere w/inexpensive switchers like 136Xs but if I pursue this further it'll be w/apparently more robust implementations like the MAX1771 I referenced. And maybe shielded coils & an RC or LC output filter.
i am curiouse about the 1771. I got two amps to work without squeal using the 1363 but when i was hooking up preamps it was horrible. The 1 watt and 2 watt amps work great though. weird. I think the 1771 has enough milliamps to make a sweet amp.
The one thing that would make me very happy is a MAX1771 (or other, I'm not picky) circuit good to 400v and about 10-20ma. That is a project I don't know enough about to tackle, but want to design very badly. I read some of that DIY Audio thread and there's some discussion in there I've got to do more research on about the different topologies mentioned.
That's not that hard really. It's making the design compact and low noise (err no noise really) that's the kicker. Getting a good gain and phase margin is the trick, but it's not a very easy to do without lots of feedback knowledge.
I plan on eventually revisiting my HV SMPS designs but as is usually the case I am swamped with school and other projects.
I'd like to eliminate the guesswork by having different schematics that people can build on the same board for their voltage needs, essentially adjusting a few parts for max stability and lowest noise at whatever voltage level one chooses. But as anybody who has done this type of design work would know, it's not very easy to get past about a 10-20x voltage boost off of the input supply. It really depends on the design though as some converters are limited to 50% duty cycle while others can hit close to 100% duty cycle.
So I think I'm bored enough to dig up my old design files and finish the design I started forever ago. I got up to a working prototype last time but was never fully satisfied with my work. I think with another years worth of practice and a lot more knowledge when it comes to tubes, I should be able to nail down a solid design that I'd be comfortable sharing with the community.
zambo - I got two amps to work without squeal using the 1363 Interesting. Did you (or would you) share info about those in some other thread?
Guess I've done a lot of 136X nixie PS talk here given this thread's title:)
Cliff - Sounds good & that'd be nice & generous of you:)
BTW I'll see & post what I find after playing around w/the MAX1771 bit coming my way. Will probably try 220v or so in my tests to keep w/250v rated parts.
I finished a 200V, 50 mA design last night (for an 8-16V DC input). I'm going to keep stepping up the voltage by 50V until I get to maybe 400V, but the input voltage requirements will increase as well with this change. Hopefully all of these different levels will fit nicely on the same board.
I probably won't be doing a through-hole version of this design though as the oscillator is running in the 1 MHz range and TH parts don't play well with switchers at this high of a frequency. The parts count is relatively low (again I'm doing current-mode discontinuous designs, they fit our needs well) and shouldn't be more than $10-$20, even cheaper if you are smart and order samples of the IC from TI. I'll resurrect my old thread on this when I have everything prepared.
A little OT but !
Cliff , thanks for the great work you have put in on this , but I have to ask.How old are you ? You keep saying "when I get in from school I will look at this etc". Where I come from we leave school at 16 years old. Your knowledge seems to exceed a young pre 16 year old.
I'm 24 and a fresh PhD student, so I'm always somehow busy between that, gigging and building stuff (not to mention the girlfriend..). I think I joined these forums when I was about 16 though.. :D
The 1363/1364 switchers use the Linear Technology LT1619 running at 300kHz into a open bobbin flyback transformer. Note that the numbers are never removed, however part of the manufacturing includes covering completed units with a polyester conformal coat to keep the windings in place and limit corona leakage from the high voltage nodes.
Generally, audible noise is a function of three things:
1. If the input is not cleanly bypassed the input voltage is pulled at a frequency dependent on the inductance of the wiring and can actually destroy the device due to over dissipation of the switching FET. The 330uF capacitor supplied should be placed as close to the power pins as possible: Source-to-Capacitor-to-Switcher
2. If the load is very inductive, the 1uF output capacitor and the load can form a parallel resonant tank circuit. If the resonant frequency is any close upper or lower harmonic of the 300kHz switching frequency the device will pump the load and possibly destroy the rectifier or switching transistor because of capacitor over voltage or diode reverse leakage. The solution to this is to insert a series resistance to lower the Q or increase the output capacitance to push the resonant frequency below the lowest resonant subharmonic of the switching frequency.
3. Secondly, this switcher uses a PFM control scheme that skips cycles when the load does not pull the output down below the recycle threshold resulting in a "frequency" of operation less than the 300kHz internal setting. The core can emit sound via magnetostriction if the PFM beat frequency is in the audio range. To disable the power saving burst mode and force continuous switching, a resistor (About 130 ohms) can be inserted between the LT1619 pin 5 and the 10mOhm current sense resistor.
See current data sheet for precautions against conductive shielding and "Fingers" on the transformer core or FET.
jt
Thank you for the confirmation and additional information about the operation of your SMPS, Taylor. I'm really looking forward to using your devices for my project.
Quote from: taylotjpt on February 09, 2011, 06:21:07 AM
The 1363/1364 switchers use the Linear Technology LT1619 <snip>
Generally, audible noise is a function of three things:
<snip of loads of great info>
jt
Wow. Thanks for all the great info & suggestions from someone who knows:) Will consider these esp. as I'm going back to the 1363/1364 switcher for my little project. If/when I do that & get anywhere I may start a new thread w/different title.
The pre-built MAX1771 addressed one issue for me (no high freq artifacts, no audible (electromechanical?) emissions) but introduced a more problematic one (a low freq buzz). Tried various filtering networks both @ input & output w/that MAX1771 implementation and could not reduce the low freq buzz substantially
in my application.
Let me be clear though, YMMV and I'm not an EE. My total guesses WRT my MAX1771 issues would be a ground problem stemming from the way it was wired in on the bench, e.g. perhaps that implementation/architecture is more sensitive to this. IMO the precise behavior of these HVSMPSs in specific scenarios, esp. in cases for which they were not explicitly designed (e.g. audio), can be difficult to predict (esp for a layman:).
Quote from: taylotjpt on February 09, 2011, 06:21:07 AM
The 1363/1364 switchers use the Linear Technology LT1619 running at 300kHz into a open bobbin flyback transformer. <snip>
... To disable the power saving burst mode and force continuous switching, a resistor (About 130 ohms) can be inserted between the LT1619 pin 5 and the 10mOhm current sense resistor.
In the event one wants to try the above, I suppose lifting pin #5 and bridging it back to its pad using an approx 130R resistor be a way to do this:
(http://i2.photobucket.com/albums/y33/pbcubed/LT1619_burst_disable.jpg)
P.S. sorry again for this slightly OT post, but while we're on the subject....
Any time someone engineers a solution for me, it's not off topic, it's appreciated. Thanks! This is something I will very likely do when I play with these.
Quote from: defaced on February 10, 2011, 02:10:39 PM
Any time someone engineers a solution for me, it's not off topic, it's appreciated. Thanks! This is something I will very likely do when I play with these.
But
lifting pin #5 and bridging it back to its pad using an approx 130R resistor is easy to say, not to do - scratch one #1363 :icon_rolleyes:
Found I could not lift a pin on these little buggers, best I can do is the entire 4-pin chip side tilting the chip up (solder "wipe" method)... Then bridge 3 back down & one use 130R. In theory. If PCB pads aren't lifted, etc. Not sure that's possible either w/my pedestrian gear.
taylotjpt - If you visit here again could you please
point out/mark the Rsense resistor in defaced's or my pic (perhaps easier to lift) or(<<-- nope, that won't work either as the 130R must be between pin #5 & the FET/Rsense
juncture) give other thoughts on this? Perhaps its just not possible w/"normal" gear on these tight little SMD puppies.
run the 1363 into a reservoir cap. it works like a charm now and no whine to it. I used a cap---resistor ( 1 ohm) cap---b+ and it works great now.
Quote from: zambo on May 18, 2011, 06:50:53 PM
run the 1363 into a reservoir cap. it works like a charm now and no whine to it. I used a cap---resistor ( 1 ohm) cap---b+ and it works great now.
It's funny, I was just thinking about this. I've a 1364 in hand I was thinking of trying the 130R thing on, but if a C-R-C like that fixes it that'd be great.
BTW what cap values did you use & what are you driving with this (e.g. tube/topology/B+/current if you know 'em)?
I am driving a whole amp. 2 x 22uf 350v caps and 10ohm resistor. http://www.youtube.com/embed/rkhOqfyzdN4 i show it at the end of the vid if you skip the playing parts.
Quote from: zambo on May 18, 2011, 08:00:41 PM
I am driving a whole amp. 2 x 22uf 350v caps and 10ohm resistor. http://www.youtube.com/embed/rkhOqfyzdN4 i show it at the end of the vid if you skip the playing parts.
Like your playing:)
Well I've tried filtering circuits incl CLC & CRC in my application (headamp discussed previously) with the 1393/1394 and could not eliminate the high-pitched squeal entirely.
Using a Simple R-C filter calc ( http://www.muzique.com/schem/filter.htm (http://www.muzique.com/schem/filter.htm) ) it seems your filters corner freq is about 700hz, which appears to block the high-freq oscillations from passing to your tube B+ in your application.
But are you saying this filter also stopped the high-pitch noise from emanating from the unit itself too? This would be curious as it would then have affected the switchers operation as well (such that it stopped oscillating).
Last night I dove into this once more 1st adding your filter (have 22uf/250v caps around) & it may have help a bit in the headamp's output but did not change the emanating oscillation (which may be creeping other parts of the circuit as my 1394 is not yet shielded). Then I suffered through adding a 120R resistor at pin #5 as discussed before & bridged the other pins w/wire-wrap wires. It was hell. Took several tries & an hour or so w/my equipment.
But it was worth it as it entirely eliminated the high-pitch noise - both that emanating from the unit & downstream in the headphone output.
(http://i2.photobucket.com/albums/y33/pbcubed/HV_1394_120R.jpg)
The only noise left is a very, very low-level hum that goes away when I place a finger on the 1394's coil spool OR better place a simple grounded shield over it.
If we could get Taylor Electronics Services to include the 130R SMD resistor for pin #5 for 1393 and/or 1394 (with optional pins/jumper to bypass providing original operation) I think the 1393/1394 could be a low-cost HV SMPS solution for lots of projects.
I'll email taylotjpt about this & if others did too maybe they'd consider it. The whole thing would likely perform even better w/o the wire hackery I had to botch in to do it.
BTW Don't even think about doing the hack above w/o very tiny soldering tip, steady hands, a few 139Xs to kill, a smaller resistor than mine, wire-wrap, time & patience.
BTW I'll be building this proto headamp out with a simple open-ended grounded sheet-metal cover over the switcher & a 2nd order LP filter using 47R/100uf/470R/10uf (e.g. http://www.electronics-tutorials.ws/filter/filter_2.html (http://www.electronics-tutorials.ws/filter/filter_2.html) ).
I am not getting any noise from the unit its self?
.
Wow that is some seriouse micro soldering Cfcubed! I am glad it worked out finaly. I have never used the 1364 you show pictured but only the 1363. It may be that i am pulling as many ma as possible through the tubes and that seems to quiet them down as well. You are using it to power a couple preamp tubes i think right? I think they dont pull as many ma and the switcher works in the sonic range without the max load on it if that makes sense. Either way, I am glad its working now!
Quote from: zambo on May 27, 2011, 04:43:24 PM
I have never used the 1364 you show pictured but only the 1363. It may be that i am pulling as many ma as possible through the tubes and that seems to quiet them down as well. You are using it to power a couple preamp tubes i think right? I think they dont pull as many ma and the switcher works in the sonic range without the max load on it if that makes sense.
Yep pre-amp tubes & their lower draw was probably causing the squeal due to:
Quote from: taylotjpt on February 09, 2011, 06:21:07 AM
... this switcher uses a PFM control scheme that skips cycles when the load does not pull the output down below the recycle threshold resulting in a "frequency" of operation less than the 300kHz internal setting. The core can emit sound via magnetostriction if the PFM beat frequency is in the audio range.
BTW 1393 & 1394 share the same datasheet & parts look identical so I think they are the same thing packaged in different ways.
Quote from: iccaros on May 27, 2011, 03:35:46 PM
I am not getting any noise from the unit its self?
Are you telling me you've used these switchers & gotten no squeal
OR are you asking me whether I'm getting noise from the unit itself?
As I said in my last post, with the crazy mod I did, inserting the resistor under pin # 5 as taylotjpt mentioned, I do not get any high-pitched noise/squeal at all anymore. Not from the unit itself & not in its output. I only get a barely audible, low-freq hum that goes away with a grounded metal shield (esp. over the coil bobbin (or place a finger on it)).
Bottom line tho w/the experiences we've had think its hard to recommend these switchers for use in audio, at least w/o on-board support of that resistor (and users adding a shield). Except maybe for specific schematics in which the 1393/1394 has proven to behave well (e.g. perhaps zambo's design).
Quote from: cfcubed on May 28, 2011, 08:35:43 AMI only get a barely audible, low-freq hum that goes away with a grounded metal shield (esp. over the coil bobbin (or place a finger on it)). <<< The low-freq hum went away in the (more proper) buildup, its working well w/no noise of any kind. So a shield should be unnecessary & wouldn't want one close to the bobbin anyway (re: shorted turn/specsheet)
Bottom line tho w/the experiences we've had think its hard to recommend these switchers for use in audio, at least w/o on-board support of that resistor (and users adding a shield). Except maybe for specific schematics in which the 1393/1394 has proven to behave well (e.g. perhaps zambo's design). <<< PM'd taylotjpt about possibility of on-board support for the resistor & haven't heard back. May try a direct email to TES before giving up on it.
I think I know my issue but I am looking for suggestions
So I have one of these SMPS with the output going to a 33u cap with a 5k 5watt to a 33uf cap where I then connect my small amp (I build a AX84 HO with submin tubes)
I want to pull my heaters from the 12 volt supply but it looks to my wall adapter like a dead short and it will not power..
I had before 2 meg going to ground from the last cap and the heaters worked, but the the 5K was dropping 151 volts across it.
So I think the 5K is so high compared to the heaters causing the power supply to think its shorted. .
Hi,
As max1771 seems to have some instability issues, and 555 seems to have too low current, what do you think about the cheap cicuit used here, with a lm393 here ?
http://threeneurons.wordpress.com/dekatron-stuff/variable-dekatron-spinner-kit/ (http://threeneurons.wordpress.com/dekatron-stuff/variable-dekatron-spinner-kit/)
It would be to power two a 12ax7 preamp, with lr8 linear regulator for each ones...
the 555 does not sink current and is not the limiter of current in most designs, the IRF 740 has too high of an turn on resistance, but replacing with and 840 which has a lower turn on resistance can allow upwards to 150ma, by some reports.
But to your post, it looks like a good design, low MA range >15ma, which is OK for preamps, and some small amps. Merlin Posted a simpler version in one of the threads, the only way to know is to try, I find that a lot of SMPS made for Nixie's are noisy on audio CKT..
SMT... ::) Fogetaboutit... For relatively light load, one of these cheapo inverter (http://www.ebay.ca/itm/Car-DC-12V-24V-AC-220V-Power-Inverter-Adapter-USB-/280758843245?pt=LH_DefaultDomain_0&hash=item415e87f76d) does the trick.
More discussions here (http://www.diyaudio.com/forums/tubes-valves/202151-12-volt-300-volt-inverter-question-tubes.html).
(http://i406.photobucket.com/albums/pp142/printer2_photo/guitar%20amp/inverter.jpg)
Jaz
awesome Greg.. tone is in the fingers, and yours has it in spades.. share your design?
lol, thanks man. Design is dead simple. Gain stage one is 100k plate / 1.5k cathode / .022 cap out to 1 meg volume / gain stage 2 is the same / 220k grid leak and 5k grid stop on the 6v6 power tube/ 400R cathode. power supply is 47uf cap / 10R / 22uf / 100r/ 22uf . heaters run on 6 volts dc. just took a lead off of the power in and dropped it over 4 diodes. ( in4007 ) to get to 6 volts. wire them just like 6v ac. 4,5 hot 9 grounded on the 12ax7. 2 hot 7 grounded on the 6v6. works with 6k6 as well and is a bit quieter. OT is 5k primary single ended to 8 ohm speaker.
Bypass caps on all the cathodes of 22uf on the pre and 220uf on the power will make this thing bark. If I did that mod i would change the first coupling cap from .022 to .0022 and see how that sounds. If that wasnt good I would switch it with the second coupling cap. Thanks for looking!
Quote from: jazbo8 on March 21, 2012, 02:39:39 AM
SMT... ::) Fogetaboutit... For relatively light load, one of these cheapo inverter (http://www.ebay.ca/itm/Car-DC-12V-24V-AC-220V-Power-Inverter-Adapter-USB-/280758843245?pt=LH_DefaultDomain_0&hash=item415e87f76d) does the trick.
More discussions here (http://www.diyaudio.com/forums/tubes-valves/202151-12-volt-300-volt-inverter-question-tubes.html).
(http://i406.photobucket.com/albums/pp142/printer2_photo/guitar%20amp/inverter.jpg)
Jaz
This has really peaked my interest.
I'm gonna see if I can find one of those and get something workable out of it. Would be super neat to get a compact, high-voltage supply that could allow the use of either an external DC adapter, or a gel battery, to go "Tubbin' on the road".