Hi!
I'm building myself a mic preamp and i'm having some problems with B+ part of the PSU (the rest works well) from this site:
http://www.gyraf.dk/gy_pd/g9/g9pd.htm
I would like to have aroud 300VDC out of it. I was told to have 230VAC at the input to get around 300VDC at the output, and change R35,36 (517R) to 470R trimer to be able to trim output voltage . To test the PSU on its own i should pull 2-3mA of current.
So i used what i had, my input voltage to the regulator was 210V, i wired 100K resistor in series with led diode to get 2,5mA of current at the output. With this i got 250VDC after the rectifier and the same at the output. But i couldn't trim the output voltage.
I tried to get help at another place, but the answers i got are only confusing me, people seem to not agree, or i don't understand what they are saying. Anyway, i'm getting very very frustrated with this thing because i should go to France in a few days to test my diy preamp which needs this psu. As you probably imagine, finishing this circuit means A LOT to me.
I have two questions if anyone who really knows what this is about is willing to help me;
Can i get from 245VDC to 310VDC at the output of regulator if my AC input is 230V?
If this is not possible, how many volts AC do i need to get from 290 to 310VDC at the output of regulator?
TL783 datasheet:
http://www.datasheetcatalog.com/datasheets_pdf/T/L/7/8/TL783.shtml
I will have more questions about feedback resistors, minimum current for regulator to regulate etc, but maybe it's better if i ask step by step.
Miha
I'm building myself a mic preamp and i'm having some problems with B+ part of the PSU (the rest works well) from this site:
http://www.gyraf.dk/gy_pd/g9/g9pd.htm
I would like to have aroud 300VDC out of it. I was told to have 230VAC at the input to get around 300VDC at the output, and change R35,36 (517R) to 470R trimer to be able to trim output voltage . To test the PSU on its own i should pull 2-3mA of current.
So i used what i had, my input voltage to the regulator was 210V, i wired 100K resistor in series with led diode to get 2,5mA of current at the output. With this i got 250VDC after the rectifier and the same at the output. But i couldn't trim the output voltage.
I tried to get help at another place, but the answers i got are only confusing me, people seem to not agree, or i don't understand what they are saying. Anyway, i'm getting very very frustrated with this thing because i should go to France in a few days to test my diy preamp which needs this psu. As you probably imagine, finishing this circuit means A LOT to me.
I have two questions if anyone who really knows what this is about is willing to help me;
Can i get from 245VDC to 310VDC at the output of regulator if my AC input is 230V?
If this is not possible, how many volts AC do i need to get from 290 to 310VDC at the output of regulator?
TL783 datasheet:
http://www.datasheetcatalog.com/datasheets_pdf/T/L/7/8/TL783.shtml
I will have more questions about feedback resistors, minimum current for regulator to regulate etc, but maybe it's better if i ask step by step.
Miha
hi
with a 230 vac transformer, after the rectifier you should be getting something in the order of 1.414 times that voltage, say, 320 volts.
you say that you're getting 250volts after the rectifier something is wrong there, can you check your wiring again?, that capacitor should be smoothing things out.
looking at the spec sheet, the regulator has a minimum current take of 15ma, so once you have sorted out the input to the regulator you need a bigger load, so if you want 15ma, divide that into 300v and that's the load that you require, the additional load through the voltage setting resistors will help too.
the voltage is set as follows
vo = vref[1+r2/r1]
vref is the drop over the reg.
you only want to drop about 20 volts, pick your values to suit.
hope that this helps
bill.
ps. you might want to get rid of the 470R resistors either side of the regulator, you don't have much headroom to regulate with, i dont know what the current take is with your preamp, however, if it is about 50ma you are going to lose about 5volts in these resistors alone.
with a 230 vac transformer, after the rectifier you should be getting something in the order of 1.414 times that voltage, say, 320 volts.
you say that you're getting 250volts after the rectifier something is wrong there, can you check your wiring again?, that capacitor should be smoothing things out.
looking at the spec sheet, the regulator has a minimum current take of 15ma, so once you have sorted out the input to the regulator you need a bigger load, so if you want 15ma, divide that into 300v and that's the load that you require, the additional load through the voltage setting resistors will help too.
the voltage is set as follows
vo = vref[1+r2/r1]
vref is the drop over the reg.
you only want to drop about 20 volts, pick your values to suit.
hope that this helps
bill.
ps. you might want to get rid of the 470R resistors either side of the regulator, you don't have much headroom to regulate with, i dont know what the current take is with your preamp, however, if it is about 50ma you are going to lose about 5volts in these resistors alone.
Hi Bill,
My first tube needs 3mA, second 15mA. I will check my wiring again (i'm quite sure it's ok, but anyway), meassure transformers one more time and get custom transformer. Now i'm using one 20VA EI trafo and one very old 15VA toroid. Btw, my input voltage to the rectifiers was 210VAC.
Thanks for help, i will be back
Miha
My first tube needs 3mA, second 15mA. I will check my wiring again (i'm quite sure it's ok, but anyway), meassure transformers one more time and get custom transformer. Now i'm using one 20VA EI trafo and one very old 15VA toroid. Btw, my input voltage to the rectifiers was 210VAC.
Thanks for help, i will be back
Miha
Hi,
it looks like my problem were old transformers i was using. Like i said, one was Ei, the other very very old toroid (insulation outside is almost black, looks like transformer was getting very hot). Anyway, when i checked my psu with variac, i got what i should.
I called workshop where i always buy custom transformers and they told me new one will cost 20 euros, that's for 230VAC primary, 12VAC (for heaters) and 220VAC (for B+) secondary, both 30VA.
I'm not sure if 220VAC on secondary is ok if i want to get from 245 to 310VDC out of regulator?
Datasheet for TL783 regulator says input to output difference should be more than 25V and less than 125V. If i have 230VAC input and 245 to 310VDC output, i guess i'm fine.
I want it to be variable because i have some other tube circuits where i need regulator like this one.
So, is 220VAC on secondary side of trafo ok for what i need?
Miha
it looks like my problem were old transformers i was using. Like i said, one was Ei, the other very very old toroid (insulation outside is almost black, looks like transformer was getting very hot). Anyway, when i checked my psu with variac, i got what i should.
I called workshop where i always buy custom transformers and they told me new one will cost 20 euros, that's for 230VAC primary, 12VAC (for heaters) and 220VAC (for B+) secondary, both 30VA.
I'm not sure if 220VAC on secondary is ok if i want to get from 245 to 310VDC out of regulator?
Datasheet for TL783 regulator says input to output difference should be more than 25V and less than 125V. If i have 230VAC input and 245 to 310VDC output, i guess i'm fine.
I want it to be variable because i have some other tube circuits where i need regulator like this one.
So, is 220VAC on secondary side of trafo ok for what i need?
Miha
Hi!
Bill if you will read this; thanks a lot for all help you gave me,it was very helpful. Circuit works well since i changed transformers for B+. One of them have 280, the other 230VAC and both work well.
Reason for my confussion was that i used too low input voltage, so the regulator didn't work.
I have one more question about the psu: is there any difference in sound between solid state and tube rectifier? I know it is in git.amps, but i'm not sure if it's the same in preamps.
I'm asking because i have space in chasis of preamp i built for at least tube rectifier, maybe also regulator (OA2 for example).
Regards from Miha
Bill if you will read this; thanks a lot for all help you gave me,it was very helpful. Circuit works well since i changed transformers for B+. One of them have 280, the other 230VAC and both work well.
Reason for my confussion was that i used too low input voltage, so the regulator didn't work.
I have one more question about the psu: is there any difference in sound between solid state and tube rectifier? I know it is in git.amps, but i'm not sure if it's the same in preamps.
I'm asking because i have space in chasis of preamp i built for at least tube rectifier, maybe also regulator (OA2 for example).
Regards from Miha
Glad to hear that you have everything sorted out. Good news indeed, as for the difference between solid state and valve regulators, i can't tell you.
I think that I have tin ears.
THe main considerations are; valve regulators are big and bulky, and will take a lot of damage, overloads etc., they basically need their own power supply as well what with additional heaters and the like.
Whereas LM317s with a power transistor round it, and a other components, are rock solid, and small. The downside is that when they fail, they fail all at once, there is no 'accidental' short cct.
Why don't you breadboard one first then try it before committing yourself to fitting one permanently?
kind regarsd
bill
I think that I have tin ears.
THe main considerations are; valve regulators are big and bulky, and will take a lot of damage, overloads etc., they basically need their own power supply as well what with additional heaters and the like.
Whereas LM317s with a power transistor round it, and a other components, are rock solid, and small. The downside is that when they fail, they fail all at once, there is no 'accidental' short cct.
Why don't you breadboard one first then try it before committing yourself to fitting one permanently?
kind regarsd
bill
Yeah, i think i could use one of my transformers to try this. Btw, TL783 psu is breadborded too, at the moment. But since it's nice, simple and very usefull i will make pcb for it.
I found this schematic with EZ80 rectifier:
http://www.jogis-roehrenbude.de/Verstaerker/SRPP-VV/1a.jpg
It looks similar to what i use now, except for rectifier and dual out voltages. I think i will give it a try.
Btw, do you suggest something else? I can get EZ80 type tubes quite cheap here (nos Tesla and some russian models).
Regards from Miha
I found this schematic with EZ80 rectifier:
http://www.jogis-roehrenbude.de/Verstaerker/SRPP-VV/1a.jpg
It looks similar to what i use now, except for rectifier and dual out voltages. I think i will give it a try.
Btw, do you suggest something else? I can get EZ80 type tubes quite cheap here (nos Tesla and some russian models).
Regards from Miha
hello
go to www.duncanamps.com and download his power supply modelling tool, in there you can model many different type of rectifiers in various modes too.
picking the right rectifier very much depends on your load, in yuor case it's pretty light, the ez80 will push out 270ma with the piv somewhere north of 900v, so you should be well and truly ok.
bill
go to www.duncanamps.com and download his power supply modelling tool, in there you can model many different type of rectifiers in various modes too.
picking the right rectifier very much depends on your load, in yuor case it's pretty light, the ez80 will push out 270ma with the piv somewhere north of 900v, so you should be well and truly ok.
bill
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