# Aikido HV power supply PCBs



## rsabo

I've drawn up some power supply boards for the Aikido headphone amp I've been planning/putting off for a year or so. I did this because a) I like the look of PCBs over point-to-point; and b) it'll help me avoid screwing up by, say, crossing wires, or mixing up the AC wires with the DC wires, etc. 

 I've done two boards; one power supply, and one regulator. The power supply is the one in the Aikido docs, the regulator can be seen here. (Go down to "A simple solid-state high-voltage regulator")

 I'd appreciate it greatly if someone can point out any errors or improvements.

 Power Supply:
 Schematic:
http://img145.imageshack.us/img145/850/aikidops1km.png
 Board:
http://img444.imageshack.us/img444/8...dopsbrd0tp.png


 Regulator:
 Schematic:
http://img215.imageshack.us/img215/3...kidoreg3sn.png
 Board:
http://img215.imageshack.us/img215/6...oregbrd7we.png


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## AndrewFischer

Quote:


  Originally Posted by *rsabo* /img/forum/go_quote.gif 
_I've drawn up some power supply boards for the Aikid..._

 

You've just done the next thing on my personal to do list. I'll give this a serious look later today.

 At first glance, I'd make the traces wider.

 The regulator schematic needs to be cleaned up, but that's cosmetic.

 Using Eagle? Are you willing to share your .brd and .sch files?


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## AndrewFischer

Besides wider traces, I have a few more minor items

*Rectifier board:*

 C5,C6 and C7 might be to close. Dunno. Depends on parts, but there isn't much room on the silk screen.

 C5,C6,C7 and L1 are very close to the edge of the board. May be a non-issue. Depends on parts and case.

 Have you thought about making the board wider and putting D5 between L1 and the capacitors? That might let you move that power trace.

 Are the spaces on the ground plane wide enough? They look kinda small to me?


 Cosmetic:

 Rotate some of the resistors around so the silk screens don't overlap with other parts.


*HV Regulator*

 There is an error in the schematic. The base of the TIP50 connects to C9 diode.

 I didn't check the tubecad schematics for errors, so maybe you fixed something wrong in the original...

 Your schematic is a mirror of the one in tubecad. If you draw it the other way, you won't have to cross the transistor base leads over and the schematic will be cleaner looking. It will also be easier to see errors. (minor cosmetic suggestion)

 I'll take a look at the layout after you fix the error.


 (if my comment are at all harsh or terse, I apologize. I've got a ton of work to do and wrote this as quickly as I could)


 A.


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## n_maher

Glad to see some people discussing the Aikido here!

 At the risk of exposing my inadequate knowledge what do both of you plan on doing for a heater power supply? It's the one thing on my Aikido that I have yet to really flesh out.

 Nate

 P.s. Here's my Aikido parts stash.


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## AndrewFischer

Nice stash. I plan to go cheaper on the passive parts. 

 Ever since I read Eric Barbours 1995 Glass Audio article, l've wanted to build an Octal headphone amp. The cost of building Barbour's amp with new parts kept me away. I've been considering building a mu-follower using NOS odd ball tubes. I've drawn up a few and done some SPICE simulations. NOS 8SN7s sell for about $4.00. 

 Then I read about the Aikido. Broskie's boards require both tubes to run the same filament voltage, so that more or less eliminates using odd balls like the 8SN7. Darn. I don't think his Octal boards can be configured as headphone amplifiers. Drat.

 So I have to decide to either not use his boards or use 9-pin tubes. I'm 90% of the way to ordering a set of 9-pin boards from him.

 Once I decide on tubes, I can figure out power supplies. 

 Assuming I go with 9-pin, 12V tubes:
 12AU7 300mA 12BH7 900mA x2 for stereo or 2.4A @ 12.6V

 Idea #1 is to use unregulated DC for the tube heaters. Use a STEPS board for the line filter, rectifiers and capacitors. Since theses are all indirectly heated tubes, the filaments are *not* in the signal path. Choose caps for their ability to kill 60Hz noise, not for overall frequency response. Blackgates are not needed. 

 I'd have to use an off-board transformer. That's more power than you can get from a 60mmX60mm Amveco transformer and too much current for an LM317T. I'd use the old trick of series connected diodes to cut down the DC voltage to close to what the tubes need. 



 Idea #2 is regulated filament power. Use two STEPS boards, one for each channel. 1.2A@1.6V is well within what I can get from a 60x60mm transformer. 1.2A is too much for an LM317 but not for an LM338.


 At the moment I'm leaning towards #1. Traditional tube gear uses unregulated heater power and it works fine. DC should help with noise. As long as I leave room in the case, I can always swap to #2 if #1 doesn't work well.


 There is also the possibility of using a step-down switcher. Maybe an LM3448????


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## dsavitsk

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_At the risk of exposing my inadequate knowledge what do both of you plan on doing for a heater power supply?_

 

If you only have a 6.3V secondary, you'll never get 6.3VDC out of it. Try AC before you do anything else. Just ground the center tap (or better, bias it up a few volts) and you should be fine. It is largely a myth that AC heaters on indirectly heated tubes are noisy. This is only the case if done improperly.

  Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_P.s. Here's my Aikido parts stash._

 

For all the money you have spent on tubes (and the attenuator which will make almost 0 sonic difference), replace those solens with something decent. They really are garbage in the signal path.


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## AndrewFischer

Idea #3 -- Scale up the STEPS to fit the 35 and 50VA Amveco transformers. 
 I suspect a single LM338T will overheat with a PCB mounted heatsink. National has designs for using 2 or 3 LM338s to increase capacity. That should work.

 I hadn't considered this as a new PCB wouldn't be cost effective for just me. But if might be for a run of 10 to 20 boards. For fun, I'll design a regulated linear suitable for the Aikido heaters. It will include a way to float the heaters to a fraction of the B+.


 If 3 or 4 people are interested in splitting the cost, we can PM about getting a small run of boards made.


 Edit: Might be impossible to fit on the 160x100mm maximum board I can make with the non profit version of Eagle. Any suggestions for a free CAD program?


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## Nerull

Just wondering dsavitsk, you said the attenuator will make almost 0 difference, I was wondering how you came to this conclusion? I'm curious, because I want to know if it's a big waste of money or not, because I guess I can't trust a lot of audiophile reviews, and I agree with your capacitor reviews (having tested capacitors of the same make myself).

 Not to derail the thread or anything, I was just curious and have almost never seen a comment such as that.

 ~Tom


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## AndrewFischer

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_If you only have a 6.3V secondary, you'll never get 6.3VDC out of it._

 

That's not quite true. Since 4 tube heaters are a more or less constant load, an unregulated DC supply will work. 
 With no load, the output will be about 1.414*6.3 - voltage drop across the diodes. Somewhere around 8VDC. As the load increases that will fall. A lot. How much it falls depends on the VA rating of the transformer, the regulation of the transformer and the size of the capacitors. 

 I do agree that AC is worth a try on indirectly heated tubes.


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## dsavitsk

Quote:


  Originally Posted by *Nerull* /img/forum/go_quote.gif 
_Just wondering dsavitsk, you said the attenuator will make almost 0 difference, I was wondering how you came to this conclusion?_

 

It's a little bit of an over statement. I was just trying to say, in comparison to the capacitor choice, the amount of good it will do is small. Think of it this way, If I had some dollar amount to spend between coupling caps and a volume control, I'd likely put at least 75% of that into the caps. If you include power supply caps, up that to 90%. Yes, I know that the Aikido is supposed to be not very PS dependant, but I've heard plenty of other circuits that were not PS dependant be improved greatly by a better PS. So, I guess, for me, if the sonic benefits are the concern, and not the channel matching, or the nice clicky feel of the stepper, then I wouldn't be investing in a stepper until I had pretty high quality caps. 

 In Nate's case, I am assuming that he has super jumbo caps on the output to use it as a headphone amp. Even there, I'd likely use ASCs instead of the Solens, but whichever, I'd at least bypass them with something high quality -- Like a 1uF Auricap at a minimum. It will do more good than harm. But, I'd also try it both ways to see the distinction.

 Anyhow, it is easy to test how big of a difference a stepper will make. Use a pot to set an amp at an appropriate volume, take it out and measure it, and use a pair of resistors to form a similar voltage divider. You can quickly, and cheaply, figure out whether you think it is an improvement. To my ear, I think a PEC pot sounds about as good as two resistors, and in fact sounds better than two metal film resistors.

 -d


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## n_maher

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_If you only have a 6.3V secondary, you'll never get 6.3VDC out of it._

 

I have a separate trafo for the heaters. Quote:


 Try AC before you do anything else. Just ground the center tap (or better, bias it up a few volts) and you should be fine. It is largely a myth that AC heaters on indirectly heated tubes are noisy. This is only the case if done improperly. 
 

Thank you for the advice, my concerns are mostly centered on how to ground the heater 1/4B+ as recommended and also how to adjust the voltage of the heater PS to make sure that the tubes are seeing something close to 6.3V.

  Quote:


 For all the money you have spent on tubes (and the attenuator which will make almost 0 sonic difference), replace those solens with something decent. They really are garbage in the signal path. 
 

I respectfully disagree on all counts. One, the grand total of what you see there in tubes is less than $100, which doesn't seem like much for 13 tubes, does it? Two, I've experimented pretty extensively comparing pots to SA's and in every case I've thought the stepper sounded better, _to my ears._ That said I'm using the stepper because I already had it, it'd been sitting in a box for a year. Three, I've heard the Solens used as output coupling caps and thought they sounded nice. However, since I haven't actually started building anything I'd love to hear some alternate suggestions. I need something on the order of 47uF+, I couldn't find much out there that fit that description. I'd love to find some Sprague caps, but the Ebay supply hasn't yielded anything lately and no one stocks them.

 Also, the high voltage power supply I'll be using is a custom design, tube regulated one so I agree 100% with you on that front. The three ASC's that you see in my stash are all for the power supply.

 So if this seems like a threadjack, hopefully the Aikido specific discussion will be seen as helpful.


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## dsavitsk

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_I have a separate trafo for the heaters.Thank you for the advice, my concerns are mostly centered on how to ground the heater 1/4B+ as recommended and also how to adjust the voltage of the heater PS to make sure that the tubes are seeing something close to 6.3V._

 

Just make a voltage divider from B+ to ground. So, use a 220K resistor, and a 71K5 resistor in series, and connect the center tap between them. It is also a good practice to parallel a small electrolytic (50uF or so, but what ever you have around will be fine, and quality does not matter at all, just be sure the V and heat ratings are high enough) with the resistor to ground (the 71K5 in this case.) Works like a charm.

  Quote:


 Two, I've experimented pretty extensively comparing pots to SA's and in every case I've thought the stepper sounded better, _to my ears._ 
 

Fair enough 
	

	
	
		
		

		
		
	


	




  Quote:


 Three, I've heard the Solens used as output coupling caps and thought they sounded nice. However, since I haven't actually started building anything I'd love to hear some alternate suggestions. I need something on the order of 47uF+, 
 

I do like the ASCs marginally more than the solens, but since you already have the solens, I wouldn't throw them out. My experience is that bypassing the solens does a world of good. So, pick your favorite cap and put one that is from 1 to 2% the value of the larger cap (.47 to 1uF here) in parallel. I think PIOs work well here, but any high quality cap will work fine. Auricaps are pretty standard and are quite good.

 Didn't mean to pick on your parts choices, Nate. 
	

	
	
		
		

		
		
	


	




 -d


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## n_maher

Quote:


  Originally Posted by *dsavitsk* /img/forum/go_quote.gif 
_Just make a voltage divider from B+ to ground. So, use a 220K resistor, and a 71K5 resistor in series, and connect the center tap between them. It is also a good practice to parallel a small electrolytic (50uF or so, but what ever you have around will be fine, and quality does not matter at all, just be sure the V and heat ratings are high enough) with the resistor to ground (the 71K5 in this case.) Works like a charm._

 

Thanks, I think I actually understand all that. 
	

	
	
		
		

		
		
	


	




  Quote:


 Didn't mean to pick on your parts choices, Nate. 
	

	
	
		
		

		
		
	


	



 

I sincerely appreciate you taking the time to have a look at them and will never take offense to someone else's point of view on things like this. It's not like there is a wealth of knowledge about the Aikido as a headamp to pull from (at least I couldn't find much) so it's great to hear some feedback about part selection.


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## looser101

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_It's not like there is a wealth of knowledge about the Aikido as a headamp to pull from (at least I couldn't find much) so it's great to hear some feedback about part selection._

 

Latest impressions:
Hamilton mini-meet/ mod session with pics!!!

 Good luck with your builds!

 ~Renato


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## gsteinb88

Quote:


  Originally Posted by *AndrewFischer* /img/forum/go_quote.gif 
_That's not quite true. Since 4 tube heaters are a more or less constant load, an unregulated DC supply will work. 
 With no load, the output will be about 1.414*6.3 - voltage drop across the diodes. Somewhere around 8VDC. As the load increases that will fall. A lot. How much it falls depends on the VA rating of the transformer, the regulation of the transformer and the size of the capacitors. 

 I do agree that AC is worth a try on indirectly heated tubes._

 

Unless im mistaken, i believe that math is wrong. To calculate the RMS voltage (that is, the DC voltage youre going to get off of an AC line) you divide the peak voltage (in this case, 6.3v) by the square root of 2, not multiply it. Youre never going to get a higher voltage than the peak voltage of the signal from a rectification circuit, even unregulated. So that would put the maximum DC off of a 6.3v center tap at about 4.47v. 
 Then again, i could be wrong, im in the middle of about 5 hours of studying right now (and being a bad student and nipping off to check head-fi
	

	
	
		
		

		
		
	


	




 )


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## dsavitsk

Quote:


  Originally Posted by *AndrewFischer* /img/forum/go_quote.gif 
_That's not quite true. Since 4 tube heaters are a more or less constant load, an unregulated DC supply will work. 
 With no load, the output will be about 1.414*6.3 - voltage drop across the diodes. Somewhere around 8VDC._

 

Yup, I've done the math a ton of times, but in practice it never works. If you don't insist on the regulator, use super low dropout diodes, and don't mind significant ripple, you might pull it off. I did it with a CRC filter with each C = 22000uF and the R = 0R39, and just got enough voltage, and that was to only run one heater. Adding 3 more drops it more, and increases ripple.

  Quote:


 Unless im mistaken, i believe that math is wrong. To calculate the RMS voltage (that is, the DC voltage youre going to get off of an AC line) you divide the peak voltage (in this case, 6.3v) by the square root of 2, not multiply it. 
 

No, you use your method when you are using a ful wave rectifier, but here we are using a bridge. Now get back to work.


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## rsabo

Thanks for your responses, everyone. Even the "off-topic" posts are very informative. Personally, I'd been planning to use a tread for the heaters, but had not put much thought or research into it.

 changes:
 -traces wider all around.
 -ground isolation increased
 -parts shifted around
 -redid traces on reg board

 There's a lot of unused room on the PS board. I can probably shift some more stuff around and add in a "V1/4". 

*
 [size=small]ps:[/size]*
 schematic is unchanged.
 board:
http://img157.imageshack.us/img157/1...brdrev29ua.png
*
 [size=small]reg:[/size]*
 schematic:
http://img187.imageshack.us/img187/4...opsrev25li.png (much prettier, also, actually correct)
 board:
http://img261.imageshack.us/img261/2...brdrev27wn.png

 I'd be glad to offer up the .brd/.sch files; but my server is currently out-of-commision. Whomever's interested, send me a PM.


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## AndrewFischer

The rectifier board is looking better. 

 Can you move the trace connecting C5,L1,D5 from the ground plane to the other side of the board?
 Will C1 to C4 fit? Anywhere the silkscreen overlaps is a somewhere you'd better get out the calipers. 
 Adding the voltage divider for the filaments is a great idea.
 Eventually you should move around the part names so they don't overlap. That can wait until you've got the parts placement complete. Doesn't matter at all if you get the boards made without silk screen.


 Regulator schematic looks a lot better. 

 As you most likely already figured out, the resistors dissipate a fair amount of power. R3 and R4 are going to run warm at 1.45W each. I haven't looked at anything else, but plan for heat. You may need to increase spacing. 

 Move the trace that goes under C9 closer to the center of the cap. It gets close to a pad when it doesn't need to. I see a better alternate route. Maybe the autorouter didn't. 

 Move the R2-T2 trace. It is close to pads on T1.

 C8 and C9 might be too close. Not sure.


 That's all I see in a quick look. I haven't checked the boards against the schematic. Eagle should catch those errors. I also haven't checked any of the parts. For example I have no idea if the transistor pinouts are correct or not


 And check your PM. I'll take you up on the files. I can host them if you'd like.


 Andrew


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## AndrewFischer

I just realized that 14.5K 2W or 3W resistor is going to be hard to find. Did you find a source? Plan to use 15K instead?

 I wonder if the original used 2 or 3 resistors in parallel or if 14.5K is there to make all the numbers come out even. Maybe the real device used 15K and everything was a little off???


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## rsabo

It changes with whatever voltage you use, if I'm reading it correctly. And I'm not really planning to build it to 300V, maybe somewhere closer to 200. I'm actually multitasking b/t playing a game and reading head-fi now, so I'm not positive about this, but the caption below the schematic on TCJ says it sets the output voltage. The way I'm almost sure it works is

 (((desired output voltage * 100) - 1000) / 2)

 to get what is R2 and R3 on the board.

 so, for 300 V (as in the TCJ schematic)

 30000 - 1000 / 2 = 14500

 it's ugly, but it works.

 edit:
 for my 200 V:
 20000 - 1000 =19000, /2 is 9.5K

 and, since, according to broskie, if output voltage is > 300, the second PNP can be omitted, and the two resistors replaced with just one. Might make parts selection a lot easier.


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## AndrewFischer

That all makes sense. Vceo on the MJE350 is 300V. 

 Does the TIP50 need a heat sink?


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## rsabo

New stuff happened.

 [size=small]*ps:*[/size]
 schematic:
http://img406.imageshack.us/img406/7...opsrev3zz8.png
 board:
http://img406.imageshack.us/img406/6...brdrev3qi7.png

 [size=small]*reg:*[/size]
 schematic:
http://img409.imageshack.us/img409/2...regrev3du5.png
 board:
http://img406.imageshack.us/img406/3...brdrev3yv1.png

 changes:
 -resistors moved around to provide better cooling.
 -error in reg schematic fixed, and added to board.
 -added the resistor divider to the ps board.

 Not sure if I should move the traces (the new ones) away from the top, or away from the diode.

 Also, in regards to setting output voltage, I think you can adjust D3 in order to change the reference voltage. That changes the voltage going through R1, which changes the current going through R2 and R3, whose value can then be potentially changed to more easily obtainable values. I'm not knowlegeable to know whether changing the reference voltage will have any other effects however.


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## AndrewFischer

Here is a possible filament supply. I'll include my thoughts later today when I've got some time. 

 The unregulated borrows heavily from the STEPS. D5 and D6 are optional and often not needed. The regulator is 95% from an example in the National datasheet for the LM 338.








 This supply is called the MEPS. That's the exclamation a Conehead makes on realizing a STEPS provides insufficient power.


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## AndrewFischer

Some thoughts on a filament power supply for the Aikido.

 AC filament power is worth considering. Indirectly heated tubes don't pick up too much noise from the heaters. I'll be using AC heaters when I first power up my Aikido boards. 

 DC will reduce noise. My initial idea was to use a STEPS board to provide unregulated power around 14 V. I'd leave out the regulator. A series connected diode string would cut the voltage down to something very close to 12.6VDC. If I ever switched to 6 volt tubes, I'd just swap the primary to series connection, cutting the output voltage in half. Just one problem. The largest transformer that will fit on a STEPS is 25VA. At typical tube complement needs just over 30W. 

 I decided to step-up the STEPS and the MEPS was born.

 The unregulated power is derived from Tangent. Matching Vunreg to the output is critical at the higher currents. If Vunreg is too high, we will dissipate too much power in the regulator. If Vunreg is too low the regulator will drop out. There needs to be a margin to allow for line voltage fluctuation. I want to allow for post construction Vunreg adjustments without having to swap transformers. The Aikido will work with a wide range of tubes. The filament supply should support that with a minimum of work.

 MEPS keeps the original over spec'd line filter. The transformer is an Amveco 35 or 50VA unit. I plan to have jumpers for both the primary and secondaries, allowing for the maximum possible output choices from a single transformer.

 Rectifier diodes can be any TO-220 units that can handle the current and power. Two or three optional series diodes follow the bridge. You would use these when needed to drop the unregulated voltage a little. I can see needed this when swapping to tubes that use less power. With 6Volt tubes, these diodes could dissipate a few watts, so I will leave room for heat sinks.

 I have several ideas for the regulator. The above schematic is idea #1.

 An LM317T is limited to 1A. That isn't going to work. Moving up to the LM338 gets us 5A. That is enough for 12V tubes but not 6. Power dissipation is a problem. The dropout voltage is around 2.5V. To get a safe margin, Vunreg is going to have to be 3 to 6V higher than the output.


> 6V*2.4A = 12.8W
> 12.8*4 = 51C


That is with a perfect heat sink! I decided to split the heat across two LM338s. The increase in cost isn't much. You can't just put two 3 pin regulators in parallel. If you do that, one ends up getting all of the load, then goes into thermal or current limit. This regulator circuit, updated from the LM338 data sheet, uses the two .1 ohm resistors to sense the current going two the two regulators. The op-amp adjusts the top regulator to keep the load balanced. 

 National has an ancient application note, LB-51, that describes an alternative way to do this. It is worth a read.

 This will work for 12V tubes. 6V tubes draw twice the current and will dissipate twice the power in the regulator. With a regular NPN linear regulator, the amount of power dumped into the regulator is nearly as much as what goes into the tubes. That's not a good design.

 That leads us to idea #2.

 A LDO regulator, like an LM1084 has a 1.5V drop out. Some of the LT parts from Linear are 1V. Thats much better but we need to keep the input voltage less than 3V over Vout. One way to do this is with a switcher feeding a linear regulator. Since there are some interesting 6V tube choices, I'll draw up a #2 MEPS over the next few days.

 Comments are welcome.

 Andrew


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## AndrewFischer

I changed the HV rectifier to use tubes instead of silicon. (thanks to rsabo for the eagle files!)






 This circuit uses a pair of 6X4 tubes in a full wave rectifier. A single 6X4 is good for about 70mA@300V output from a capacitor input filter. Rather than figure out if that is enough power for every possible Aikido configuration, I included the option to parallel two 6X4 tubes. If you don't need it, don't put one in the socket. 

 Why not use a larger capacity tube like an 6CA4/EZ81? Most of them are getting expensive. The EZ81 is $12-$20.

 6X4s are cheap. $4.00 last time I checked. A 6X4 is small. I might be able to get this to fit in the same space as the solid state board.

 I don't claim or expect this to have any sonic advantage. A tube rectifier will soft start. No need for a time delay. 6X4s are so cheap that it doesn't change the cost too much. The larger choke might be the bigger hit.


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## rsabo

Cool 
	

	
	
		
		

		
		
	


	




 Some possible errors that I saw on the MEPS schematic:
 -Pin 1 on R7 isn't connected to anything. Unless I've misunderstood how trimpots work, it needs to connect to ground.
 -There's no hole/wirepad for B+/4.

 A twelve-volt supply will work with 6V tubes, using jumpers J1 & J4. Not sure whether this would double the current capacity, however.

 It also looks kind of like A1 on V2 in the tube rectifier is shorted to ~.


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## AndrewFischer

Quote:


  Originally Posted by *rsabo* /img/forum/go_quote.gif 
_-Pin 1 on R7 isn't connected to anything. Unless I've misunderstood how trimpots work, it needs to connect to ground._

 

A potentiometer is a resistor with a sliding tap. With the knob fixed somewhere it can be modeled as two resistors.






 Measure the resistance from pin 3 to ground. It will be R1. If you disconnect pin 1 from ground, the resistance at pin 3 is still R1. Doesn't matter if pin 1 is grounded or not. When I lay out the board, I will likely end up grounding pin 1. I've left it open for now.


  Quote:


 There's no hole/wirepad for B+/4.
 It also looks kind of like A1 on V2 in the tube rectifier is shorted to ~. 
 

I'll fix those. My CVS server died last night. Its back up, but I don't have access to the files right now.



  Quote:


 A twelve-volt supply will work with 6V tubes, using jumpers J1 & J4. Not sure whether this would double the current capacity, however. 
 

I'd forgotten the Aikido boards will let you put the filaments in series. Putting the tubes in series cuts the current in half. We won't need the other design. The MEPS will work. 
 There is still the question of using a switcher as a pre-regulator. The end result would be more efficient. If I find some time I'll play around with a design. 

 Layout is next.


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## dsavitsk

Quote:


  Originally Posted by *AndrewFischer* /img/forum/go_quote.gif 
_Why not use a larger capacity tube like an 6CA4/EZ81? Most of them are getting expensive. The EZ81 is $12-$20.

 6X4s are cheap. $4.00 last time I checked. A 6X4 is small. I might be able to get this to fit in the same space as the solid state board._

 

So you are going to use 2 $4 tubes + 2 hard to find 7 pin sockets instead of one $12 tube and one easy to find socket? So, all in all, you might save $4, though there is the additional cost of slightly more board space and probably more shipping from multiple vendors. 

 Plus, and most importantly, this is a bad idea as the tubes will likely be unbalanced which means all the current being drawn from one instead of the other which will damage the one and ignore the other. Just use an appropriate rectifier and be done with it. NOS EZ80's are $10 and chinese GZ34's are $12 at AES.

 Also, even if you do insist on DC filaments, all of the accoutrement is wasted time and money. A simply regulator is more than enough as there is almost no noise passed from heater to tube, especially in an amp that uses lowish mu tubes and only has mu/2 gain.

  Quote:


 A potentiometer is a resistor with a sliding tap. With the knob fixed somewhere it can be modeled as two resistors. 
 

But it is standard safety precaution to connect both ends of the pot and the tap to one of them. This way, if something goes wrong with the pot while you are adjusting it (and this is common as these things are cheap and not built for a lot of adjustment) you still have some resistance.


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## AndrewFischer

I had planned to use a single 6X4. Antique Electronics Supply sells the tubes for $4.00 and 7 pin sockets for $0.95. I haven't figured the total power needed yet and wasn't sure if the 70mA you can get from a 6X4 would be enough. 

 However you are right about balance.

  Quote:


 Just use an appropriate rectifier and be done with it. 
 

Ok. I'll figure out how much power I need and then come back to this. 



  Quote:


 A simply regulator is more than enough as there is almost no noise passed from heater to tube, 
 

I know that if you get the filament bias right, almost nothing gets passed into the signal. But what else am I supposed to do in my spare time 
	

	
	
		
		

		
		
	


	





 The caps around the rectifiers are not required. But they are penny parts.


 I could leave the input filter off, but I'd rather build a board that can have them. I may end up using this for something other than a filament supply. Besides I already have the parts on hand.

 This is about as simple a linear regulator as I could come up with. Maybe I made a math error, but it looks to me like a single LM338 is going to overheat.

 LM338Ts are $2.50 each from Digikey. The LF 356 is $1.10. The heatsink is $1.28. 

 A single LDO could work but would require careful parts selection. 

 I've got a few LM2678Ts sitting around. I've always wanted to learn how to lay out a simple switcher. Maybe I'll play with that tonight...


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## AndrewFischer

I've redrawn the unregulated HV schematic with a single tube. 
 At the moment it has a 6V4/EZ80. The 6CA4/EZ81 is the same pin out. I suppose you could use the same PC board for a higher current supply.

 I haven't ruled out using a single 6X4 or 12X4. Its a lot cheaper and smaller, I just need to figure out if it will provide enough power.

 Here are some possible rectifier choices, the approximate max output current, the maximum value for C5 and where I got the numbers from.
 6X4 70mA 10µF RCA manual
 6V4 90mA 50µF http://www.drtube.com/datasheets/ez81-philips1970.pdf
 6CA4 150mA 50µF RCA manual


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## AndrewFischer

Today's tubecad blog announced the Rev. B Aikido boards. 

http://www.tubecad.com/2007/01/blog0096.htm

 The new mono boards support a much wider range of tubes. You can also have 6 and 12 tubes on one board. The new stereo board will work as a headphone amp. 

 Still thinking about the 6X4 supply. 70mA * 250V is 17.5W. While that should be enough, Brooksie likes to run his tubes at high idle currents. 

 I'm sure there are some combinations that will work with a 6X4 and others where it won't be enough. I'll design something that will work with the 6V4 or 6CA4.


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## AndrewFischer

Here is the latest version of the HV supply board. 






 I've moved the choke off board. I'm not aware of PC mounted chokes in the 1 to 10 H range. For now, L1 is a small open frame Hammond. They are about $8 to $10. I chose some capacitors off of the UPW spec sheet, so I'd know what sizes to use on this board layout.







 This needs work. I've got some silk screens overlapping. C1 is a little close to the rectifier tube. UPWs are 105C rated. I think I'll move it a little to the right and the tube a little to the left. There is wasted space at the bottom too. . .

 Edit to remove old layout. New one to follow


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## AndrewFischer

I spent a few minutes on the layout this morning. The diode is back. I've moved the tube away from the capacitors. The board is a little smaller at 3.9"x2.7". Not done yet. The diode is cutting into a trace. Board is still too big.


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## AndrewFischer

I'm a EE. So far, I haven't done any circuit analysis. That just isn't right.

 The HV supply will be putting out about 300V to 360V. With a 6V4 the maximum current output is 90mA. Using ohms law, the impedance of load is going to be about

 300V/.090A to about 360V/.090A 

 or3.3K to 4K. If the current is about 35mA it will be more like 10K. anyway... The 120Hz impedance of C1 should be about 1/10 of the load or somewhere between 300Ω and 1KΩ at 120Hz.

 C1 = 1/(2pi*120Hz*300Ω) to 1/(2pi*120*1000Ω) or about 4.4µF to 1.3µF

 Even at the highest possible load we might see with a 6V4, 47µF is overkill.

 For best results, L1 should be somewhere between 4H and 10H. As the current goes down, the choke's inductance needs to go up. 

 I'm going to change C1 back to 10µF. It will be easier on the tube and make little difference at the output. I may make C2 a little bigger.


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## AndrewFischer

I've fixed all the errors I'm aware of. 

 Partial bill of materials.

Transformer: Hammond 272BX (300V 100mA) or 273DX (350V 90mA)
Choke: Hammond 156L, 157M or 193B. 8H 259Ω 157M is a good fit. 193B is overkill.
V1: 6V4
C1: 10µF 450V Nichicon UPM or UPW. 22µF 450V UPW will also fit.
C2: 220µF 315V Nichicon UPW. 330µF 250V and 100µ 400V are alternates
C3: 22µF 200V UPM
C4: Undecided.


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## AndrewFischer

Updated unregulated board.







 Changes:

 Output bypass cap can be a Sprague 716P in the .1µF to .22µF 400VDC range or a smaller box cap.

 C5, the cap on V1/4 is now a .1µF cap. Several box caps from Wima and others will fit the flexible pad sizes here. Need to fix the pour here... Oops.

 Silk screen values for the resistors.
 Changed diode to a 1N4007. Part is really cheap and could be left off. 

 Other parts shifted around to make room for the Orange Drop.


 I'm still thinking about using a 6X4 rectifier. Most of the tube complements I've been looking at draw 50mA or less driving my Sennhiesers. That's well within the 70mA 6X4 limit.

 But this board is more flexible. If the 90mA 6C4 isn't enough a 6CA4 drops in.


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## AndrewFischer

I've sent this off to Olimex for production.







 Many small changes.

 RN65D resistors
 Holes changed to match Olimex drill rack.
 Tiny changes to meet Olimex 10mil design rules.
 Better silk screen text.
 10mil min silk screen for Olimex.


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## AndrewFischer

I spent a few days looking at linear regulators suitable for an Aikido. Output between 250V-350V and 50mA-100mA.

 I played SPICE with all sorts of LM317 based regulators. This is a good starting point for anyone thinking about following that route: http://www.national.com/an/LB/LB-47.pdf

 In the end, I decided to go with Broskie's simple regulator. Changing the zener from 10V to 8.4 drops the current in the two resistors to 8.4mA. 15K resistors instead of 14.5K sets the output to just over 250V. The lower current reduced the heat coming from each resistor to just over 1W. The MJE350s are loafing at about 1/4W each. The TIP50 runs around 5W to maybe 9W. It will need a heat sink. The rest of the parts aren't heating up much.






 I made a new layout with a decent sized heatsink for the TIP50. I left room for heat sinks on the MJEs. The resistors are bigger too.






 For now, the board is single sided. Not quite ready to send out.


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## rsabo

Would you mind running over the calculations for the heat output of the TIP50?

 Also, I don't really see the need to design a new reg board - there is one. If you think mine is inferior in whatever way, fine; however, anything else is just a duplication of effort, imo.

 edit:
  Quote:


 The TIP50 runs around 5W to maybe 9W. It will need a heat sink. 
 

If I'm reading the datasheet correctly - and google backs me up on this in at least one spot, in the quick time that I've checked - the TIP50 can dissipate up to 40W, meaning that there may not be a heatsink required, and if there is, a rather small one will do.

 apologies for any grammatical complexity, I'm not quite awake enough yet.


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## AndrewFischer

Figure 4:

http://www.fairchildsemi.com/ds/TI/TIP50.pdf

 The TIP 50 can dissipate 40W at 25C. As it heats up, the power drops to zero at 150C. To keep inside the operating area and have a little margin, I'd like to keep the device below about 105C.


 The Fairchild data sheet doesn't give the thermal resistance of the case but the ST does.

http://www.st.com/stonline/products/...re/ds/4147.pdf Thermal data is at the top of page 2.

 Thermal Resitance Junction-Ambient is 62.5°C/W. Without a heat sink my Aikido will heat the junction to about 600°C and the transistor will fry.

 Thermal Resistance Junction-Case is 3.125°C/W. The thermal resistance of the heatsink is about 2.6°C/W. 
http://www.aavidthermalloy.com/cgi-b...=530002b02500g

 The thermal resistance of the insulator is about .67°C/W http://www.aavidthermalloy.com/produ...ilms_iso.shtml

 (2.6+3.125 +.67) *10 ≈ 64°C Add in the 30 to 40 that could be inside a tube amp and the TIP50 is inside the 105C limit at 10W.

 This shorter heat sink might work too: http://www.aavidthermalloy.com/cgi-b...=529802b02500g. I'd rather take up the extra space and not worry about figuring exact thermal conditions.

 TIP50 Power dissipation I got from running SPICE simulations. As a rough estimate you can just take the load current. The current in the load is going through the TIP50's collector-emitter. My worst case is 100mA load, Vin = 350V and Vout = 250V. W = I*E. .100X(350-250) = 10W. 

 Your layout is nice and compact. The TIP50 will need an off board heat sink. It doesn't say on the data sheets, but one of the leads is likely bonded to the case. Insulate. If you stick with exact original schematic, the two 14.5K resistors need to be at least 2W devices. Also check the resistors you select are rated at full power at about 70C. If you need to make the resistors bigger, TO-220 resistors might be a way to keep board area down. Edit: with a 200V output and a reference change, you should be able to stick with 1W resistors. 


 I've made some small changes to the original design including a few component changes. I'm also working with a different form factor. I want these to fit in half of an Olimex SSS panel. I'm also playing with drill sizes and silk screens so I can get two boards for $27.30.


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## AndrewFischer

Quote:


  Originally Posted by *rsabo* /img/forum/go_quote.gif 
_Also, I don't really see the need to design a new reg board - there is one._

 

Some people watch TV or play computer games in their off time. I play SPICE and layout PC boards.


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## AndrewFischer

Minor changes to original design. Replace zener with IC reference. Add film cap to output. Pads to connect two mono amps. Resistor and pads for off board neon indicator. Extra gnd pad is a test point.







 The board is about ready to send out. Removed redundant MJE350 heat sinks from silkscreen. Board meets Olimex rules. Size matches the raw tube supply.


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## AndrewFischer

Browsing the TI catalog I found the TL783. The TL783 is a high voltage 3 pin adjustable regulator. It can take a 125 Volt difference between the input and output pins. Nifty. Google found me an existing regulator design that is nearly identical to what I would have done.

http://www.gyraf.dk/gy_pd/g9/g9_sch.gif

 I changed that a tiny bit and put it into Eagle.






 Resistor values are for about a 250V output. The string of zeners protect the TL783 during startup. Simple. Those are 5W zeners so the regulator will still blow up if it is shorted to ground. If you build the circuit as shown, R1 and R2 don't draw enough current alone for the TL783 to operate. The output voltage will rise if the output is not connected to a load.

 EDIT: Removed R3. With a tube rectifier it is not needed. The DC resistance of the choke and rectifier tube limit current surges. I did some checking and start up doesn't even get close to the 1N5365's short term power limits. 3.5A for 8.3mS .9A for 1S. I didn't check but it might even survive a brief short to ground.


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## AndrewFischer

3 fit on an Olimex SSS panel.


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## AndrewFischer

Sent to Olimex for production. 




 Olimex shipped the rectifier board Monday. It should be here in about a week.


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## AndrewFischer

The rectifier boards arrived today. 











 For comparison, the board to the left is from PCBPro. PCBPro has somewhat crisper silk screen, but the 10mil Olimex silk screen is fine.

 The Olimex boards have a slightly rougher cut edge then PCBPro. Not something I'd even noticed until I looked at the photos.

 For RoHS compliance Olimex has gone to immersion gold. Very nice. You can't see it in the photos but some of the PCBPro boards had significant solder puddles. Not a big deal, but Olimex is a clear winner over PCBPro here.


 Minor gripe. I sent the Eagle .brd file along with my Gerbers. Olixmex used the .brd file. In the .brd file, the board outline and the Rev 0.4 text were in non-standard Layer 121. Olimex took everything in 121 and put it in all the layers. -- So I've got copper and silk on the board outline. I've also got an reversed Rev 0.4 on the bottom. I pulled up the copper from the board outline. No big deal and looks fine. I should know better then to include a .brd file. I only sent them Gerbers for the regulator board. 

 Overall I'm quite pleased with the results. Price was good 47USD for two including shipping from Bulgaria. 

 The regulator boards should ship in about week and be here in two.



 I've decided on an Aikidio configuration. SPICE says it will idle at about 35mA for a Stereo pair. I'm going to get a transformer and choke in the 60mA range.


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## jarthel

/me wonders why there are no designs using rectifier tubes in this thread :|


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## AndrewFischer

Quote:


  Originally Posted by *jarthel* /img/forum/go_quote.gif 
_/me wonders why there are no designs using rectifier tubes in this thread :|_

 






 My board uses a 6V4 or 6CA4.


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## AndrewFischer

The regulator boards are here. This time I didn't leave my .brd file in the zip I sent to Olimex. They used my Gerbers. 







 I'm pleased with the way these turned out. $36.30 for 3 including airmail from Bulgaria. PCB Express would have been $200 for two. Batch PCB would charge $32.50 for one or $77.50 for 3.


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## AndrewFischer




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## AndrewFischer

The iron arrived today. I've got a busy weekend but I'm going to try and find time to do a smoke test into a dummy load.


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## AndrewFischer

I powered up the rectifier board. It works. The 380V output is a bit higher then my simulations predicted. Didn't take long to figure out why. The Hammond transformer is spec'd at 115V but the wall power here is 121V.That's 5%. I'm using a 15k load. At 380V that's about 25mA. The 270CX is 275-0-275 at 65mA. 

 A 270AX or JX would have been a better match. I think I'll just run the amp at 300V to 350V. Time to hit the tube handbooks.


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