What sort of power transformer(s) can you obtain? The topology of the PSU will be governed by the available "iron".
Well i can get E core transformers i can't get a trasformer that can do high voltage and the low voltage for the heater in one box tho. I can get 2 individual transformers. And the mains voltage in my country is 230volts.
Power supply
You could use an isolation transformer...as they tend to be easier to obtain. This will give you appx 320 volts of HT ...since it is a preamp perhaps you could regulate it down towards your target voltage.
Let us get an exact voltage you want & we'll go from there & get it drawn up for ya!
______________________________________Rick.........
You could use an isolation transformer...as they tend to be easier to obtain. This will give you appx 320 volts of HT ...since it is a preamp perhaps you could regulate it down towards your target voltage.
Let us get an exact voltage you want & we'll go from there & get it drawn up for ya!
______________________________________Rick.........
Attachments
hi richard, aren't isolation trasformers 1:1? how will the voltage become 320? Could you please expain. I'm new to this. And the schematic says anything between 250 to 300 volts will work
230v RMS. 325v peak. The caps will be charged to this value, minus diode drop, more or less, in a SS design.
Voltages??
Daniel:
Transformers and most all "ratings" or designations of AC voltages are given as RMS voltages...What is RMS? It stands for Root Mean Squared.
RMS is derived from the mechanical generation of AC....It also has mathmatical significance...........The waveform we are talking about is called the Sinewave. Ever heard math people utter Sine or Cosine?........This waveform shape is what they are refering to.....very common in mathmatics.
The RMS voltage is .707 of its Peak.....The easy way to understand it is the total area of one upper curve of a sinewave is equivalent to 70.7 percent of the square box of the same time as one upper curve of a sinewave............Look at my drawing here, see if it makes sense for you.
_______________________________________Rick........
Daniel:
Transformers and most all "ratings" or designations of AC voltages are given as RMS voltages...What is RMS? It stands for Root Mean Squared.
RMS is derived from the mechanical generation of AC....It also has mathmatical significance...........The waveform we are talking about is called the Sinewave. Ever heard math people utter Sine or Cosine?........This waveform shape is what they are refering to.....very common in mathmatics.
The RMS voltage is .707 of its Peak.....The easy way to understand it is the total area of one upper curve of a sinewave is equivalent to 70.7 percent of the square box of the same time as one upper curve of a sinewave............Look at my drawing here, see if it makes sense for you.
_______________________________________Rick........
Attachments
Daniel:
It looks like this schematic will work ,but it has some specific components....looks a little like overkill for your application as it has several "extra" voltages....and it has some FET devices which you may not be able to get from the sounds of things....your simple preamp deserves a simple power supply....look for an LM 317 or LM 123 series regulated high voltage supplies...if you note these say they work on low voltages but are "floating" regulators and with some supporting circuitry can indeed regulate high voltages.
The low voltage filiment regulators are a much simpler design & are easier to build.
Do a search on High Voltage regulators...trying to keep it simple.
I found some schematics in Morgan Jones book "Valve Amplifiers".
I can't reprint them here in this forum , but I'm positive schematics abound thruout the net.
Ther are some other issues we will have to talk about concerning implementing & integrating you design into a workable project. Hang in there we'll get this built & up and running for ya!
___________________________________Rick.............
It looks like this schematic will work ,but it has some specific components....looks a little like overkill for your application as it has several "extra" voltages....and it has some FET devices which you may not be able to get from the sounds of things....your simple preamp deserves a simple power supply....look for an LM 317 or LM 123 series regulated high voltage supplies...if you note these say they work on low voltages but are "floating" regulators and with some supporting circuitry can indeed regulate high voltages.
The low voltage filiment regulators are a much simpler design & are easier to build.
Do a search on High Voltage regulators...trying to keep it simple.
I found some schematics in Morgan Jones book "Valve Amplifiers".
I can't reprint them here in this forum , but I'm positive schematics abound thruout the net.
Ther are some other issues we will have to talk about concerning implementing & integrating you design into a workable project. Hang in there we'll get this built & up and running for ya!
___________________________________Rick.............
Thanks a lot for help'n me out richard i found a schematic at DIY paradiso http://diyparadiso.com/6sn71.htm . The only problem for me is that it has chokes and finding chokes in india is very hard. Is there something that can be done
PS design
Daniel:
I came up with a cool design for your power supply it is based on the LR8N3....I didn't know they had developed a high voltage "three pin regulator" ( In 2004!) ...this simplifies everything!!!!!
Using your first schematic i'm integrating this cuircuit into a full schematic for you....using the 'common' isolation transformer.
This 'special' regulator brings up one problem and requires us to make a decision on the simplicity question,.
The regulator in question is cheap and small...probably not available there in India but is easily "deliverable" by someone in the United States....you could almost attach it to a postcard!
The other question is that this high voltage setup will apply HV to the Tubes instantly....we don't want that.
The typical setup would be a delay of some twenty seconds...First the transformers for the filiments would light up , then the HV would hit the tubes some twenty seconds after.....
We can put a timed relay to bring on the Hv...set for any time delay we want...but we need to tap off the heater transformer to do it.....it just adding to complexity but a regimen start-up procedure would have to be adhered to religiously!
By the way what is the availability of low voltage transformers...say 12 to 24 Volts?
My "Paint" program accidently deleted the cuircuit I was drawing up for you...I'll redo it gain tonight
_____________________________________Rick.............
Daniel:
I came up with a cool design for your power supply it is based on the LR8N3....I didn't know they had developed a high voltage "three pin regulator" ( In 2004!) ...this simplifies everything!!!!!
Using your first schematic i'm integrating this cuircuit into a full schematic for you....using the 'common' isolation transformer.
This 'special' regulator brings up one problem and requires us to make a decision on the simplicity question,.
The regulator in question is cheap and small...probably not available there in India but is easily "deliverable" by someone in the United States....you could almost attach it to a postcard!
The other question is that this high voltage setup will apply HV to the Tubes instantly....we don't want that.
The typical setup would be a delay of some twenty seconds...First the transformers for the filiments would light up , then the HV would hit the tubes some twenty seconds after.....
We can put a timed relay to bring on the Hv...set for any time delay we want...but we need to tap off the heater transformer to do it.....it just adding to complexity but a regimen start-up procedure would have to be adhered to religiously!
By the way what is the availability of low voltage transformers...say 12 to 24 Volts?
My "Paint" program accidently deleted the cuircuit I was drawing up for you...I'll redo it gain tonight
_____________________________________Rick.............
Attachments
wow richard thanks a lot. and i'll be able to get a 12volt or a 24 volt transformer real easy here. I'll also see if the regulator is available.
PS
Daniel:
Sorry for the delay...So here we go, folding one schematic into another ,this is what I came up with...a simple iso transformer for the high voltage..Two of them,each is rated for 100mA so the Max plate load of 20mA for your tubes is a breeze for it.
The capacity of you Iso transformer should be around 300 watts or so...the larger the better of course, the full wave bridge at six hundred volts per is a good safety margin, any values higher in voltage in caps is Ok depending on your component availability.
The peak inverse voltage on the bridge diodes leaves a margin, again higher is OK.
We still need to decide how we are going to apply High Voltage as written here there is NO switches for HV as we need to decide what we're going to do ...Can you find whats loosely called Delay relays? As allways scout around for your components & we'll see what is and isn't available in your area.
___________________________________Rick...........
Daniel:
Sorry for the delay...So here we go, folding one schematic into another ,this is what I came up with...a simple iso transformer for the high voltage..Two of them,each is rated for 100mA so the Max plate load of 20mA for your tubes is a breeze for it.
The capacity of you Iso transformer should be around 300 watts or so...the larger the better of course, the full wave bridge at six hundred volts per is a good safety margin, any values higher in voltage in caps is Ok depending on your component availability.
The peak inverse voltage on the bridge diodes leaves a margin, again higher is OK.
We still need to decide how we are going to apply High Voltage as written here there is NO switches for HV as we need to decide what we're going to do ...Can you find whats loosely called Delay relays? As allways scout around for your components & we'll see what is and isn't available in your area.
___________________________________Rick...........
Attachments
Thank for the schematic richard. I'll look for the delay relays. It'll take a while tho, i have my exams come'n up in a week so i gotta sit tight and study lol. I'll let you know as soon as i get the compoments. And also is the filament transformer 220 to 3volts AC?
Daniel.....OK, No the filiment transformer as noted as 9VAC...which when rectifyed comes out to 12.69 (9.0 times 1.41)..minus 1.4 volts going thru the diodes....the rest of the voltage is "disipated" thru the regulator.( The tubes of course get 6.3VDC)
Too much voltage (Within spec) going thru a regulator just wastes power & heats up the device....But there is a voltage spec that must be exceeded beyond the 'target' voltage...but not too much (Burn-up).
Before you start up on this we really should run it by the forum here to see if it has been done before by someone here & how well does it work, can it be tweeked, suggestions, etc.. Keep in touch...
________________________________________Rick..........
Too much voltage (Within spec) going thru a regulator just wastes power & heats up the device....But there is a voltage spec that must be exceeded beyond the 'target' voltage...but not too much (Burn-up).
Before you start up on this we really should run it by the forum here to see if it has been done before by someone here & how well does it work, can it be tweeked, suggestions, etc.. Keep in touch...
________________________________________Rick..........
Ah ok. I was also wondering if i can use film capacitors in the power supply as finding high voltage electrolytes aint easy here.
Yes you can use & actually best choice(Only choice?) for the bypass caps on the full wave bridge, you won't find a high enough value (10 to 60uF) for the power supply end section....yes you can string together multiples of caps to get higher values, but film caps won't get high enough to equal even the wimpiest electrolytic. besides films are usually non-polarized....that said I guess I should go back & notate which are polarized and which are not.
___________________________________Rick...........
___________________________________Rick...........
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