Look at the graphic I've uploaded. It was "ripped" from VMI. The 2nd schematic is the subject of interest. That's for a positive setup. So, turn everything upside down, to get a negative setup. IMO, it's self evident about how to squeeze 1 or more negative voltages out of a single low voltage winding. That 1/2 wave parallel topology places equal stress on all the diodes (Schottkys please) and increasing stress on the capacitors.
AnTek's web site shows a price of $35.00 for the model AN-2T350. BW, you tell the rest of us how that compares with Edcor's power trafo price.
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I've used John Ng's (Antek) toroids of a couple of projects (3 transformers) and they turned out to be typical Asian quality. You get what you pay for. In my opinion, the Edcor at $50-some (which I have no experience with) seems a worthwhile 'upgrade'. The Edcor seems to be about half the price of many other similar power transformers -- assuming I don't have some basic facts wrong.
With the cover, the Antek unit looks a bit better, IMO, but I like Edcor's graphic design (in limited quantity), and many don't.
..Todd
Thanks Eli for the tips!
One thing when I talked with BNB tubes is they didn't answer on my question whether there are different EH's or are their tubes coming from New Sensor.
Anyway I will have a talk with McShane if he at all can ship tubes over to Europe.
Have been checking in some datasheets on tubes, among those Johan recently mentioned just couple of posts back, I have to admit when I look on the curves for the 12AT7 they are in deed curvy and when I look on a ECC99 data sheet it's flat as a ruler, now there were some words mentioned earlier in this thread that the 12AT7 would match very well with KT88. Just trying to understand the interpretation going in here so the grid on KT88 must have such an "anti" curve in it's current drawing which mates well with the 12AT7 distortion signature that it would equal out the major part of the distortion, have anybody had a look on a FFT how the harmonics look like or is it done merely by voicing of the amplifier?
I think I will try the ECC99 in addition to 12AT7, hmm.. is it only JJ who manufactures ECC99, I don't feel at all so keen with JJ of some reason though I don't have yet practical experience with their tubes, I have understood they use a bit basic materials in their tubes..?
Cheers Michael
One thing when I talked with BNB tubes is they didn't answer on my question whether there are different EH's or are their tubes coming from New Sensor.
Anyway I will have a talk with McShane if he at all can ship tubes over to Europe.
Have been checking in some datasheets on tubes, among those Johan recently mentioned just couple of posts back, I have to admit when I look on the curves for the 12AT7 they are in deed curvy and when I look on a ECC99 data sheet it's flat as a ruler, now there were some words mentioned earlier in this thread that the 12AT7 would match very well with KT88. Just trying to understand the interpretation going in here so the grid on KT88 must have such an "anti" curve in it's current drawing which mates well with the 12AT7 distortion signature that it would equal out the major part of the distortion, have anybody had a look on a FFT how the harmonics look like or is it done merely by voicing of the amplifier?
I think I will try the ECC99 in addition to 12AT7, hmm.. is it only JJ who manufactures ECC99, I don't feel at all so keen with JJ of some reason though I don't have yet practical experience with their tubes, I have understood they use a bit basic materials in their tubes..?
Cheers Michael
That could be one good idea as the Antek toroids are missing the big negative voltage winding!
Another way to get the negative supply is to add windings, toroids in particular comes in very handy for that simple mod and would be more stable and cheaper.
I have done this and it works perfect, here is how you do to find out how many turns are needed:
Make 10 turns with an arbitrary wire temporary, plug in the transformer to the mains voltage and make a VAC measurement with your multimeter, let say you got 4 Volts from the temporary winding, now you know for every turn you get 0,4 Volts (4 Volt / 10 turns.. easy).
Next you have to set for a negative voltage you want, let's say 55 Volts...
now we have to remember that when we measure with a multimeter it takes the RMS value which means its not the peak voltage, BUT when we rectfire and filter the ripple voltage the filter capacitors charge up to the peak value.
For sinus shaped waveforms such as the mains voltage the peak voltage, Vpk = Vrms * 1,414 (the 1,414 is the square root of 2 and applies only to sinus, not triangular or square waves or other shapes)
Back to the equation, we found that Vrms for one turn is 0,4 Volt, so Vpk would then be 0,4 * 1,414 = 0,56
Next step is to obtain the final amount of turns to get 55 Volts for our negative supply, and we calculate it as follow.. 55 / 0,56 = 98 turns
but we make it 100 turns to compensate a bit for the diode voltage fall and for a nice and even figure.
Now we just have to add a rectifier bridge and one filter cap and we are done, Voi la!
Tried to be as pedagogic as possible so even noobs could do it but ask if something wasn't clear.
Cheers Michael
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I think Johan meant 40 W.
Oh ... -er - no, sorry. I was just looking into the future. You know? 16 x 6L6GCs nicely lined up .....
Oh ... -er - no, sorry. I was just looking into the future. You know? 16 x 6L6GCs nicely lined up .....
Nicely lined up in front of the 4 power transformers.
..Todd
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Michael,
You asked about the 12AT7. It's not that it mates specifically with the KT88. It is a matter of Physics that PP "finals" cancel even order HD products. A PP O/P stage exhibits a distortion spectrum that contains mostly 3rd and 5th order products. Unfortunately, that stuff is highly irritating. The HD spectrum of the 'T7 triode is skewed towards 2nd order products. So, small signal circuitry containing the 12AT7 mates well with any set of PP O/P tubes to yield an ear pleasing HD "waterfall" of 2nd > 3rd > 4th. OTOH, the 'T7 triode is a POOR choice in a SE amp. Can you say "wet", "syrupy" and otherwise nasty? "Horses for courses."
You asked about the 12AT7. It's not that it mates specifically with the KT88. It is a matter of Physics that PP "finals" cancel even order HD products. A PP O/P stage exhibits a distortion spectrum that contains mostly 3rd and 5th order products. Unfortunately, that stuff is highly irritating. The HD spectrum of the 'T7 triode is skewed towards 2nd order products. So, small signal circuitry containing the 12AT7 mates well with any set of PP O/P tubes to yield an ear pleasing HD "waterfall" of 2nd > 3rd > 4th. OTOH, the 'T7 triode is a POOR choice in a SE amp. Can you say "wet", "syrupy" and otherwise nasty? "Horses for courses."
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Sure, no problem. You want the B+ voltages of 456, 460, and 240V as presently in the schematic?
Hmmm, looks like things will pretty much "wash out". The toroid's edge is a small stray magnetic field. The EI has better cosmetics. Builder's choice!
Both options seem to be good values.
I am in this build now as well. If I understand the present design stage, the PS is done but the driver stage is still open for discussion and optimization.
If my 0.02 is of any value I like the 12at7 in the LTP. Mostly because I have a bunch of them. It doesn't bother me to push an output tube, but 465V seems reasonable and 50-60W output is exactly what I need for my biamp goals.
If my 0.02 is of any value I like the 12at7 in the LTP. Mostly because I have a bunch of them. It doesn't bother me to push an output tube, but 465V seems reasonable and 50-60W output is exactly what I need for my biamp goals.
Yep, exactly. Thanks!
Assuming you are using SS rectification.......what is the resistance of the transformer secondary? (one side to the CT)
Welcome aboard. Hopefully one of us will start the build soon. I've lost track of how many are going to do one. Perhaps Taj will even start one on the dinner table.