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But I have a 6.3VAC winding with a center tap I need 6 VDC.
Can someone point me in the right direction?
I need DC filaments for a Phono preamp. I thought I understood this but it seems I keep getting stranger and stranger output voltages each time I try it.
Also, what diodes are best for this? 1N5822?
Thanks!
"I KNOW you can hear it, but are you REALLY listening?"
Follow Ups:
Use PSUD2 power supply simulator at Duncan amps. You need clean DC, not pulsating. Use a choke such as a Hammond at .7 ohms or less- filter is CLC (capacitor-choke-capacitor). 6.3 volts needs a bridge, not full-wave, center tap.
6.3v looks like some 9 pin dual triodes?
try using that 6.3VAC first... if it's quiet, then don't rectify
But it's for a phono preamp. I'm pretty sure DC is the way to go with a high gain circuit.
"I KNOW you can hear it, but are you REALLY listening?"
DC heating IS the way to go in a phono preamp.
3X 12AX7s require 900 mA. at "6" V. and 450 mA. at "12" V. IMO, the best way to build a DC supply for the heaters starting with a 6.3 VAC winding is via a Greinacher ("full wave") voltage doubler and a 7812 3 terminal rectifier. Use Schottky diodes and enormous 'lytics in the cap. stack. For 450 mA. of 12 VDC, a 2A. rated 6.3 VAC winding is needed. Nothing new here about TANSTAAFL applying.
Don't forget a substantial heat sink for the regulator IC.
It's cutting things too fine to bridge rectify 6.3 VAC and then regulate down. Maybe a low dropout regulator will have enough headroom, but the doubler definitely provides the headroom necessary to correct operation of an inexpensive 7812.
Eli D.
One thing to share with you Eli:When I was using low drop rectifiers, even though they could regulate at about 3/4 of a volt differential, I found them to sound their best at equal or greater than 2.1 volts differential.
It was on filaments and I eventually ended up re-designing the Ronan regulators Phil Seig liked so much to use.
Jeff Medwin
Edits: 06/21/12
Are you saying that the rectifier type used to provide DC to indirectly heated filaments affects the sound?
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No, I said a "low drop" regulator sounds best with a 2.1 VDC differentail across it, even if it can theoretically operate and regulate at a lower differential.
Jeff Medwin
So you're talking about an application for rectifiers that has nothing to do with this thread?
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Buy Chinese. Bury freedom.
No, not at all, I never once mentioned rectifiers.
A regulator is different from a rectifier TK.
I was making a comment on Eli Duttman's suggestion about using a low drop regulator for an Ef supply.
Jeff Medwin
So, you're saying the regulator used to power the filament of an indirectly heated cathode affects the sound?
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Buy Chinese. Bury freedom.
Sure, everything, every part, every wire, every solder connection effects the sound TK.
Very elementary, no high school degree needed to know that.
Jeff Medwin
No, not every part affects the sound. Are you saying you never graduated high school?
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Buy Chinese. Bury freedom.
No, I am saying YOU need to forget whatever you learned after grade 12, go back to elementary and high school, and learn that every part inside the amp effects the sound.Cheers,
Jeff Medwin
Edits: 06/25/12
Every part inside the amp does NOT affect the sound. As for education, ignorant people generally make poor design choices.
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Buy Chinese. Bury freedom.
With all the bickering.....(give each other a big hug, please) the point of regulator was lost.
IF I understand correctly, when using one of the 78xx regulators you need voltage a couple volts ABOVE the intended regulated voltage before regulation. Maybe, expressed as a %age, 25% or 20% would do.....some help here would be nice....or perhaps a rule of thumb I could remember later.
But, that, as near as I can tell, was the point of the regulator. So, to get 6v to the heaters, you'd need maybe 8 or 9v INTO the regulator.....and apparently a different, non-CT transformer.
And while it is OT for a phono preamp, my CMOY headphone amp taught me this. I have a 24vdc wall wart which I regulated to 18v. Very stable, though no longer 'portable'. Straightforward following a drawing with no improv.
Too much is never enough
You'll need more than a couple volts headroom with the 78XX series regulators. Google "7812 datasheet" for more info. Also, the ground terminal of a three-pin regulator can be raised above ground to increase its output voltage. For example, one could use a 7805 with two silicon diodes forward biased in series at the ground terminal to achieve approximately 6.3VDC. OTOH, if you're concerned about accuracy, the LM317 only requires two resistors to set its output voltage to an exact value. It can also be configured as a current regulator, which will eliminate the startup flash of tubes like the 12AX7.
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Buy Chinese. Bury freedom.
If your transformer has a secondary source resistance of 5 ohms or so, you will get the results you get. Schottky's have less diode drop and are quieter. They are the bees knees for heater/filament supplies.
What is the spec on the transformer you are using?
Nothing to see here...
"I KNOW you can hear it, but are you REALLY listening?"
AudiodysseyWhat I do is get a tube with the same current draw
as the whole circuit and use it as a dummy load.
In your case a 6L6 or a 5687 filament draws 900mA.
A 6SN7 will get you close too at 800mA.
Unloaded voltage means NOTHING !!!
Too many variables to consider.
Load the PS and then we can work from there.DanL
Edits: 06/22/12
I rebuilt the original filament rectifier "module" I had made on a piece of clad board today. I'm going to try this.
Any chance you can explain how I do this...(this is your quote)
"It's quieter if you have the negative rail at about +40V.
Use a voltage divider from your B+ to get it."
Again, see above for my power supply schematic...
With 350-0-350 from the transformer, I dropped the 5U4 for a GZ34, LCLC this then goes to the gas regulators 0A2 and 0B2.
Thanks!
"I KNOW you can hear it, but are you REALLY listening?"
Audiodyssey
Easy -
255V PS B+
100K resistor
40V* Tap to Neg rail
18-22K resistor
Ground
Most recommend a 47-100uFd cap
from 40V to ground for stability.
* Exact voltage not important.
DanL
.
of the whole circuit and tell us what the strange readings are?
Trying to guess what your problem is based on the tiny amount of information you gave is a waste of time.
Recommending a diode without knowing the operating parameters is also a waste of time.
.
Ok, see above. I came up with 4.8VDC. I ran the CT through the negative side of a 10,000uF cap...and the cathodes into the positive. I wanted to add another section of filtering as well, but...my voltages were off.My winding is 6.3VAC with CT...2 amps plenty of current for my needs.
Do I need to tie the negative to chassis ground?
"I KNOW you can hear it, but are you REALLY listening?"
Edits: 06/21/12 06/21/12 06/21/12 06/21/12
.
Your circuit uses 1/2 the secondary for each half cycle whereas a bridge uses the whole thing on each 1/2 cycle.
The math is 3.15 V RMS for each half cycle so 3.15 x 1.414 = 4.5V peak
minus the diode drop and filtered should get you somewhere around what you got if the line voltage is a little high and/or the secondry a little higher than it should be. Without a load drawing current it will be higher as the xformer is probably rated at full load so the 4.8VDC makes sense.
Use a full wave bridge to get a higher VDC
.
Initially, I had a bridge (I think). There I used four 1N5822 diodes and just left out the center tap. My voltage was at 9VDC which was, well, too damn high. I thought it had something to do with not using the center tap, so I changed the configuration to the full wave rectifier.
I guess I just needed a larger dropping resistor in my bridge? My bridge was positive/neg out with the positive side through a 10,000uF cap, then a .2 ohm resistor, then another 10,000uF cap, then out...
Should my negative side have been to chassis ground??? That was where I was stumped and now I'm thinking it should have been grounded. This was just a dry run on a power supply for my phono preamp...
"I KNOW you can hear it, but are you REALLY listening?"
Ground is irrelevant as far as output voltage. You'll get 9V unloaded, but it will drop under load. How MUCH it will drop will depend on transformer and other losses. Due to the "peaky" distorted current waveform, the voltage drop will be more than you'd expect. You can estimate it with PSUD if you know the winding resistance, etc... here's an example with some guesses...
Voltage is a bit high - maybe 1.0 Ohm would do - but could be considerably different from this model. Current in transformer is about 1.8A. As mentioned, biasing it to a fraction of the B+ voltage (with AC bypass cap to ground) will minimize noise. But just grounding one side of the DC supply may be enough.
Audiodyssey
Use the four 1N5822 diodes
10,000uF - 3R resistor - 10,000uF
It's quieter if you have the negative rail at about +40V.
Use a voltage divider from your B+ to get it.
DanL
Use choke resistance are part of voltage drop & final tune voltage with resistor.
I don't have the real estate for a choke, Neff This is a very small Phono preamp on two chassis, the PS chassis is about 6" x "6"
"I KNOW you can hear it, but are you REALLY listening?"
Edits: 06/21/12
Make it 6 by 8 ....sound familiar DW ??
Jeff Medwin
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