Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Morgan Jones Power Supply Help.
New Posts  All Forums:Forum Nav:

Morgan Jones Power Supply Help. - Page 2

post #16 of 21

Both of Morgan Jones books are available on ebook now( <- the e in ebook is supposed to be the link )

 

As dsavitsk suggested, PSUD2 is a neat little program to play around with.(again, the P in PSUD2 is the link ), that will give a feel for what you might expect while using some of the parts suggested in the Headwize article. 

 

more math.( the m in more )

 

Yes, most all transformer specs that I have seen are in RMS, for both the primary and secondaries.(I've never seen anything but RMS)

http://www.hammondmfg.com/pdf/5c007.pdf <- Here is a design guide from Hammond, the man'f of the transformer that dsavitsk recommended you use.


Edited by digger945 - 3/20/11 at 4:23pm
post #17 of 21

 

Quote:
Originally Posted by keabler View Post


It's not that I have no idea what is going on I am just a bit confused as how to start.  

So is the VAC from the transformer the peak voltage (which makes VRMS ~ 177V)?  Is multiplying the VRMS signal from the transformer by sqrt(2) correct to calculate the DC voltage from the rectifier the correct calculation?  I don't think I'm looking at this circuit right because my numbers don't come out.

 

I do have a more-than-beginners- knowledge of electronics and I am in E&M right now so the theory isn't too heavy either.  I don't think I am starting the calculations right.

 

 

 

The documentation is somewhat confusing between figure 12 and figure 13. 

figure 12 is using an "original style" transformer arrangement, with one transformer feeding the other. NOTE! The second transformer is marked as a 24:230v unit BUT it is being fed with only 18v from the first transformer! This is important. (230v/24v)*18v=172.5v

 

 

 

Before the rest of this, FrankCooter who I respect greatly once said something like this:

"Once you build the circuit, a well stocked junk-box is worth more than any calculation or sim" 

You can plug away at the calculator until you know every voltage and current to a freakishly tight tolerance. Even after that you will sometimes find that your junk just dosnt work the way the simulation said it would... Do your best with a pencil and paper (or whatever software tools you have) but be prepared to tweak things on the fly. 

 


Here is how I would go about "solving" this. 

The voltages around the audio part of the circuit are given in figure 4. Using ohms law you can calculate the currents through the output stage, and the input stage. Add them to get the total curent for 1 channel, and double that for a stereo amp. Using this method I get 26mA, VERY close to what stixx said. Good memory, and with real tubes its sooooooo much work to get things within this margin of error.

 

 

 

I would then go through the power supply like you did with 26-27ma, and see what you get. 

 

You are correct in how you got the first 350V, but as mentioned you used 50mA where you should have used 26-27mA. Even accounting for a reasonable DCR for the choke the numbers dont add up! This could be due to a number of reasons: its possible that the mains voltage where the designer lives is always low. Its possible his transformer sagged a LOT under load. Its also possible that he used an (mains):220v or 240v transformer rather than mains:250. Mains:220 or 240v transformers are QUITE common and priced very affordably, where 250v is harder to find except for stuff designed specifically for tubes. the schematic also indicates that the voltage on the first cap is 320V, which is somewhere between what you get with a 220 or 240v secondary... As a last factor the schematic indicates that the B+ and heater transformers are separate units, which improves my confidence in the assumption that he actually used a mains:220 or mains:240v transformer. 

 

If you recalculate starting with a 240v transformer, I think you will get much closer to 220V at the output. a 230v transformer is actually about perfect. If you can find a choke with a DCR of about 1Kohms the numbers line up realllly well. The Triad magnetics C-1x for example: 15H, 20ma, 1Kohm. I'd redesign around a choke with a 30mA current rating, but eventually things make sense.  

 

Now, if you are using a transformer with a "real" 250v secondary you will need to redesign the whole thing :)


Edited by nikongod - 3/20/11 at 5:43pm
post #18 of 21

This whole psu thing is rather confusing... and to start the examples shown on the Headwize site aren't really good psu's... (back to back transformers and such).

Something along the lines of what Nikongod said would make a lot of sense and would look something like this (--> see attachment).

Actually this is not too far from what I built myself a couple years ago (was using a tube rectifier though).

 

http://s10b.directupload.net/file/u/20659/ngjwfktb_jpg.htm

 

You can use R1 to tailor your output voltage... in a tube amp you don't have to be spot on with your voltage requirement, 10% tolerance is acceptable.

 

psu_MJ.jpg


Edited by stixx - 3/21/11 at 5:14am
post #19 of 21
Thread Starter 
Quote:
Originally Posted by nikongod View Post

 

 

 

The documentation is somewhat confusing between figure 12 and figure 13. 

figure 12 is using an "original style" transformer arrangement, with one transformer feeding the other. NOTE! The second transformer is marked as a 24:230v unit BUT it is being fed with only 18v from the first transformer! This is important. (230v/24v)*18v=172.5v

 

 

 

Before the rest of this, FrankCooter who I respect greatly once said something like this:

"Once you build the circuit, a well stocked junk-box is worth more than any calculation or sim" 

You can plug away at the calculator until you know every voltage and current to a freakishly tight tolerance. Even after that you will sometimes find that your junk just dosnt work the way the simulation said it would... Do your best with a pencil and paper (or whatever software tools you have) but be prepared to tweak things on the fly. 

 


Here is how I would go about "solving" this. 

The voltages around the audio part of the circuit are given in figure 4. Using ohms law you can calculate the currents through the output stage, and the input stage. Add them to get the total curent for 1 channel, and double that for a stereo amp. Using this method I get 26mA, VERY close to what stixx said. Good memory, and with real tubes its sooooooo much work to get things within this margin of error.

 

 

 

I would then go through the power supply like you did with 26-27ma, and see what you get. 

 

You are correct in how you got the first 350V, but as mentioned you used 50mA where you should have used 26-27mA. Even accounting for a reasonable DCR for the choke the numbers dont add up! This could be due to a number of reasons: its possible that the mains voltage where the designer lives is always low. Its possible his transformer sagged a LOT under load. Its also possible that he used an (mains):220v or 240v transformer rather than mains:250. Mains:220 or 240v transformers are QUITE common and priced very affordably, where 250v is harder to find except for stuff designed specifically for tubes. the schematic also indicates that the voltage on the first cap is 320V, which is somewhere between what you get with a 220 or 240v secondary... As a last factor the schematic indicates that the B+ and heater transformers are separate units, which improves my confidence in the assumption that he actually used a mains:220 or mains:240v transformer. 

 

If you recalculate starting with a 240v transformer, I think you will get much closer to 220V at the output. a 230v transformer is actually about perfect. If you can find a choke with a DCR of about 1Kohms the numbers line up realllly well. The Triad magnetics C-1x for example: 15H, 20ma, 1Kohm. I'd redesign around a choke with a 30mA current rating, but eventually things make sense.  

 

Now, if you are using a transformer with a "real" 250v secondary you will need to redesign the whole thing :)


Thank you so much.  It makes sense to me now.  I totally understand that with electronics theory and actual operation can differ greatly (especially with tubes).  I will read some more about transformers and power supplies.  I'm glad I at least know where I am going now.  I have the undergrad lab at my disposal so I have a large capacity to tinker with the circuit.  I am pretty excited for this project I've wanted to build an amp for a while, and now I get to build an amp and get a grade!

 

Thanks again for every ones help,

 

post #20 of 21

As far as tubes go the JJ 6DJ8's have been known to be inconsistent and noisy lately.  See Jim McShanes web site.  I've stumbled across some Tesla ECC88's and E88CC's (they're both 6DJ8 equivalents) that performed suprisingly well.  Tubemomger has some (see link).  I wouldn't go overboard on exotic parts.  The Morgan jones is OK (I've built a couple of them) but not the last word by any means.  It's a good place to start and can sound quite nice in a slughly tubey, old fashioned way.  Just get standard Panasonics for the PS caps but maybe splurge a bit on a Pana FC for the output cap.  Use a couple in series for higher voltage ratings.  Bypass the output electrolytics with a polypropylene film cap, the Dayton DDFC's or Jantzen cross caps from Parts Express are high value inexpensive caps. 

 

http://www.tubemonger.com/Tesla_NOT_JJ_MPs_MINT_NOS_1979_ECC88_p/115.htm

 

Cheers, Steve

post #21 of 21
Thread Starter 
Quote:
Originally Posted by stixx View Post

This whole psu thing is rather confusing... and to start the examples shown on the Headwize site aren't really good psu's... (back to back transformers and such).

Something along the lines of what Nikongod said would make a lot of sense and would look something like this (--> see attachment).

Actually this is not too far from what I built myself a couple years ago (was using a tube rectifier though).

 

http://s10b.directupload.net/file/u/20659/ngjwfktb_jpg.htm

 

You can use R1 to tailor your output voltage... in a tube amp you don't have to be spot on with your voltage requirement, 10% tolerance is acceptable.

 

psu_MJ.jpg


Thanks, I didn't realize you could add more than one section after the rectifier.  Every thing makes so much sense now.

 

Thanks to every one who helped I am always impressed by head-fi's community.

 

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › Morgan Jones Power Supply Help.