A Triad xfmr for a voltage doubler PSU - diyAudio
 A Triad xfmr for a voltage doubler PSU
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diyAudio Member

Join Date: Sep 2009
Location: Santa Fe, Argentina
A Triad xfmr for a voltage doubler PSU

Hi everyone

I'm working on a 5watt 6BL7 PP amp that want 380V on the plates, and draw
53mA /chan (idle)
So, I decided to use a voltage doubler PSU, like in the EICO HF-87.
Will this Triad transformer be enough for my purposes?
VPS230-570 - Triad Magnetics - VPS230570 - datasheet
Filaments, instead, (2 6SL7 + 2 6BL7) will be served by another Triad, the
VPS12-3400 : VPS12-3400 - Triad Magnetics - VPS123400 - datasheet
J
Attached Files
 Documento.doc (19.5 KB, 16 views)

 20th July 2010, 09:12 PM #2 diyAudio Member     Join Date: Aug 2009 Location: Johnson City, TN I would calculate the total power dissipation of your tubes plus margin for drivers, etc, and compare it to the dissipation rating of the transformer. Tubes = 0.053A * 380V * 4 tubes = 80.56W. Then figure 20% margin for additional driver tubes, etc. 80.56 * 1.2 = 96.67W Transformer = 230 * 0.570 = 131W. Dissipation factor is thus 96.67/131 = 73.79%. Less than 75% should be good since you are using a doubler and may be pulling higher transient current compared to bridge rectification.
 21st July 2010, 02:57 AM #3 diyAudio Member   Join Date: Oct 2004 Location: Maui, Hawai'i, USA That's wonderful, but I think the voltage is going to be well above the required 380Vdc with doubler rectification. To the OP; load a copy of Ben Duncan's PSUD2: PSUD2 Then, build your power supply. Unless you know the DC resistance of the primary and secondary windings, pretty close, there will be some uncertainty, but it will get you in the 'hood. Aloha, Poinz
 21st July 2010, 04:05 AM #4 diyAudio Member   Join Date: Apr 2004 Location: Monroe Township, NJ Poinz is right. A Grienacher doubler will yield approx. 600 VDC from that Triad trafo. If you take a Triad N-77U and boost it with something that produces 25 VAC or so, say a "Rat Shack" Catalog # 273-1512, you will be on target, via a Greinacher doubler. The 820 μF./250 WVDC 'lytics Jim McShane sells, along with a pair of UF5408 diodes will do the job quite nicely. __________________ Eli D.
 21st July 2010, 04:27 AM #5 diyAudio Member     Join Date: Aug 2009 Location: Johnson City, TN True, I didn't think about the initial voltage vs doubler and accepted his values. Bridge rectified he would get 325V, more likely he will get near 600V out of it. Add a 25.2 transformer and a bridge and stack them. That will put you at 360V. If that isn't enough go with a 48V transformer and you will get 392.
 21st July 2010, 04:45 AM #6 diyAudio Member   Join Date: Aug 2009 Location: Sacramento Hello Mosquito, I am mostly with TheGimp in post number 2 but a touch more conservative. Power transformers come with a VA rating. That is volts times amps. If the connected load is purely resistive the load can equal the VA rating. A amplifier power supply is pretty ugly, volts spike, current spikes, current and voltage are not in phase. All that ugly adds up to a lot of heat in the transformer that would not happen it the load was pretty in phase sine waves of volts and amps. I would pick a power transformer with at least twice the VA of the connected load. I like to keep the temperature of the transformer cool enough to keep my hand on it for awhile, 135 degrees F or less with the IR thermometer. BTW You can reduce the voltage of the doubler by adjusting down the capacitance of the first 2 capacitors in the doubler. Think CLC smoothing. If the power supply is choke input the voltage is half. If the power supply has large C’s at the input the voltage is twice the choke input power supply. If the capacitance is reduced to some intermediate value, the output voltage is reduced to somewhere between the choke input and the full size capacitor input. This voltage reduction does not come at the expense of added transformer heating. This beats burning excess voltage in a resistor and less transformer VA is required. DT All just for fun!
 21st July 2010, 08:30 AM #7 diyAudio Member     Join Date: Sep 2009 Location: Santa Fe, Argentina Wow! Thanks for all these juicy answers! I missed to mention (my bad) that each output stage is formed by a single glass bottle containing two triodes. The 53mA figure is then for each output stage, not each triode. The math is 53mA X 2, plus safety margin. I actually modelled the thing on PSudes, and think to drop to 380V via rc cells (like in the EICO) A lossy cheap transformer will never be as the superb one in the EICO, with only 6 ohm RDC secondary winding. So I presume I'll need to drop much less. I'm sorry but I don't catch how to boost or stack a transformer (how to actually connect the windings) Can someone post a graph? At the moment I'm not at home, but later I'll post the PSUdes file I worked out, to be corrected if anything's wrong. Thanks everyone J
diyAudio Member

Join Date: Sep 2009
Location: Santa Fe, Argentina
PSU designer file

Here it is. Just change the file extension for *.psu, and it's ready to be opened in PSUdes.
By the way, DualTriode's suggestion seems to work the way I need.
Thanks again
J
Attached Files
 6BL7_D.doc (258 Bytes, 6 views)

Last edited by Mosquito; 21st July 2010 at 04:36 PM.

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