So I took a screenshot of the graph that was generated by the schematic, and I can see that the voltage of the output has increased 5.2x. I'm not quite sure how good that is or isn't. How can I calculate output power from data provided by LTspice?
http://img.photobucket.com/albums/v321/mattthegamer463/Preamp/Output.jpg
http://img.photobucket.com/albums/v321/mattthegamer463/Preamp/Output.jpg
Hi Matt,
Your results has nothing with good or bad to do. What you see is gain ie. how many times the signal has been amplified. What you see is taht with the volumepot at 50% you get 1.2Vout when feeding 250mV in. 250mV is the same as 125mV in with the volumepot at 100%. So your gain is 1.2V/0.125V= ca 10 times/20dB.
You do not count preamp output in terms of power.
So if you are in the middle of a college course in electronics I think you can get some good basic info from your teacher.
I have added a few more topologies for you to compare.
Your results has nothing with good or bad to do. What you see is gain ie. how many times the signal has been amplified. What you see is taht with the volumepot at 50% you get 1.2Vout when feeding 250mV in. 250mV is the same as 125mV in with the volumepot at 100%. So your gain is 1.2V/0.125V= ca 10 times/20dB.
You do not count preamp output in terms of power.
So if you are in the middle of a college course in electronics I think you can get some good basic info from your teacher.
I have added a few more topologies for you to compare.
Thanks for those, I can't wait to fiddle around with them.
Last night I built a PSU that was working quite well, taking the 250V rated output from the transformer and outputing 234.5V with a 1/200th of a volt ripple using high voltage caps that I already bought. Then I tried doing a filament supply but the problem is that the transformer outputs 6.3V on its filament winding, but after the bridge rectifier and the caps the output was around 5V. Apparently tubes designated "A" like a 12AX7A can run on DC or AC for their filaments, but these tubes are just normal ones. Did I mess up with my transformer selection? Will I need a new filament transformer? Sorry to be asking you so many questions, but you've got lots of answers.
I have talked to my teachers, they all laughed at me for using tubes and did little more than tell me to go get some MOSFETs. I'm going to try the public library for some books on vacuum tubes, and I've been reading lots of beginner guides on the internet.
Last night I built a PSU that was working quite well, taking the 250V rated output from the transformer and outputing 234.5V with a 1/200th of a volt ripple using high voltage caps that I already bought. Then I tried doing a filament supply but the problem is that the transformer outputs 6.3V on its filament winding, but after the bridge rectifier and the caps the output was around 5V. Apparently tubes designated "A" like a 12AX7A can run on DC or AC for their filaments, but these tubes are just normal ones. Did I mess up with my transformer selection? Will I need a new filament transformer? Sorry to be asking you so many questions, but you've got lots of answers.
I have talked to my teachers, they all laughed at me for using tubes and did little more than tell me to go get some MOSFETs. I'm going to try the public library for some books on vacuum tubes, and I've been reading lots of beginner guides on the internet.
So, basically straight from the transformer to the heaters, with a resistor to cut the 7.1V to 6.3V, with the heaters in parallel, one wire on pins 4 and 5, the other wire on pin 9?
I just hooked up the transformer to test its actual outputs, and I got 294V on the high voltage windings and 7.1V on the filament windings.
I just hooked up the transformer to test its actual outputs, and I got 294V on the high voltage windings and 7.1V on the filament windings.
Okay, I'm becoming more and more confused each day. When I measured the transformer, the DMM was set to V AC, so the readings I got (294V, 7.1V) should be the RMS value, right? Then in LTSpice when asked for the amplitude of the power waveform I should put 294 x root(2) so that I get the peak voltage of the wave.
Does my B+ have to be spot-on 300V? If so, how do I get it to that specific voltage? Same issue for my filaments, do they need to be exactly 6.3V? I've been searching for stuff about filament voltages, the datasheets say like 100V above the Cathode voltage and things, but I have no clue what the cathode voltage is or how 100V could be the limit if 6.3V is the operating voltage.
Does my B+ have to be spot-on 300V? If so, how do I get it to that specific voltage? Same issue for my filaments, do they need to be exactly 6.3V? I've been searching for stuff about filament voltages, the datasheets say like 100V above the Cathode voltage and things, but I have no clue what the cathode voltage is or how 100V could be the limit if 6.3V is the operating voltage.
Dear Matt,
I am sorry, but you should really do some reading and research on your own... while this is a forum where DIYers try to help each other, your level of knowledge is below the "minimum treshold" necessary to follow the instructions given. As such, it can even be dangerous for you to pursue further building before you learn some basics.
Anyway, when it comes to tubes, unlike transistors, they have "guidelines". If it says 300V, it can do with 250V, but most probably with 350V as well... just look the ratings for a given tube.
As I said, you have to do some more reading and research
The internet is full of information!
I am sorry, but you should really do some reading and research on your own... while this is a forum where DIYers try to help each other, your level of knowledge is below the "minimum treshold" necessary to follow the instructions given. As such, it can even be dangerous for you to pursue further building before you learn some basics.
Anyway, when it comes to tubes, unlike transistors, they have "guidelines". If it says 300V, it can do with 250V, but most probably with 350V as well... just look the ratings for a given tube.
As I said, you have to do some more reading and research
The internet is full of information!If we want a simple (1st time project) low Zout (to drive SS power amp) 12AU7 line amp why not just try a simple CC-CF setup like this circuit?
http://www.shine7.com/audio/12au7_pre.htm
You don't have to use the fancyscmancy circuit board. Just wire point to point on the sockets (and maybe some tag strips) for easy modification and expansion. Later you can mess with mu-followers and the like as much as desired.
http://www.shine7.com/audio/12au7_pre.htm
You don't have to use the fancyscmancy circuit board. Just wire point to point on the sockets (and maybe some tag strips) for easy modification and expansion. Later you can mess with mu-followers and the like as much as desired.
mattthegamer463 said:
Scroll down to DC elevation. This explains the concept. There's lots of other good stuff on that site.
Jeff
The short version: The 6.3V rating is the voltage across the heater (this is the voltage that powers it) the heater to cathode voltage rating is the maximum voltage difference between the heater and the cathode of the tube. If you put the AC heater supply across the heater but connect one of the heater leads to ground (i.e. referencing the heater to ground) and then bias the tube so that the cathode is 75V above ground potential then there is a nominal 75V between the heater and the cathode and the heater is negative with respect to the cathode.
mike
mike
12AU or ECC 82
Hi Matt.
I can help u all the way . First , the B+ voltage MUST no t be above 230v. It will give u less output. Second use DC 12V6 voltage for heating the tube. I have 3 units running at different voltage and they do not sound the same. Look for AUDIO NOTE Pre. else where that unit can be modified to your requirement. I have 2 Xtra . board that is completed for sale.
U will love it after using tube pre it very musical and got lots of slammm.
Happy building.
Hi Matt.
I can help u all the way . First , the B+ voltage MUST no t be above 230v. It will give u less output. Second use DC 12V6 voltage for heating the tube. I have 3 units running at different voltage and they do not sound the same. Look for AUDIO NOTE Pre. else where that unit can be modified to your requirement. I have 2 Xtra . board that is completed for sale.
U will love it after using tube pre it very musical and got lots of slammm.
Happy building.
I've learned how to use LTSpice well enough to figure out two power supplies (not like they're that complex) but the simulations output nothing like what the actual circuit or even common sense point to.
A 300V wave from the transformer going through a bridge rectifier, resistors and caps shouldn't end up being 297V DC, right? RMS power and all that.
So, my built high voltage circuit is working, and using the CT I get 147V AC when loaded by the components of the supply. The output of the supply is about 197V DC. If I use the full transformer winding then I get 395V DC. Two things I can’t figure out; when I have a bridge rectifier in place, I get the same output as if I only have a half wave rectifier, a single diode. Is the difference not the peak voltage, but the size of the voltage ripple? I’m having a hard time figuring out the ripple, and my oscilloscope is old and ornery and doesn’t want to display it nicely.
I’m having a hard time to get my voltage closer to 300V DC. I'm not sure how to get it lower without big high-power resistors.
A 300V wave from the transformer going through a bridge rectifier, resistors and caps shouldn't end up being 297V DC, right? RMS power and all that.
So, my built high voltage circuit is working, and using the CT I get 147V AC when loaded by the components of the supply. The output of the supply is about 197V DC. If I use the full transformer winding then I get 395V DC. Two things I can’t figure out; when I have a bridge rectifier in place, I get the same output as if I only have a half wave rectifier, a single diode. Is the difference not the peak voltage, but the size of the voltage ripple? I’m having a hard time figuring out the ripple, and my oscilloscope is old and ornery and doesn’t want to display it nicely.
I’m having a hard time to get my voltage closer to 300V DC. I'm not sure how to get it lower without big high-power resistors.
Hey Matt,
You have to use peakvoltage when simming. So multiply AC by 1,414!
About "big highpower resistors" it will be enough with std 5W wirewound found in your local shop. To build a good PSU for your pre you can easily do it by using a few cascaded RC links.
As we now can communicate by using *.asc-files things will be a lot easier. To publish them just change the name to *.txt .
You have to use peakvoltage when simming. So multiply AC by 1,414!
About "big highpower resistors" it will be enough with std 5W wirewound found in your local shop. To build a good PSU for your pre you can easily do it by using a few cascaded RC links.
As we now can communicate by using *.asc-files things will be a lot easier. To publish them just change the name to *.txt .
In your circuit:
Change Sine to your unloaded AC-voltage *1,414, should be ca 420V AC.
Also add Rser to be ca 250ohms.
Add a CRCRCRC-link of 33u-1k-33u-1k-33u-1k-33u
Now you should end up with a ripplefree DC of 280-290V.
Add a load of 10k as this corresponds to just below 30mA load.
This should be in the ballpark of the correct IRL conditions.
Change Sine to your unloaded AC-voltage *1,414, should be ca 420V AC.
Also add Rser to be ca 250ohms.
Add a CRCRCRC-link of 33u-1k-33u-1k-33u-1k-33u
Now you should end up with a ripplefree DC of 280-290V.
Add a load of 10k as this corresponds to just below 30mA load.
This should be in the ballpark of the correct IRL conditions.
Matt: A couple of other pointers.
If you seeing 7.1V out of your transformer filament windings with no load, that will drop somewhat to (hopefully) around 6.3V when powering the tube filaments, since you will be flowing current. If the voltage is still too high with everything connected up, you can add a small R (1 ohm or less) to get the filament voltage to 6.3V. The tube heaters are typically spec'd to operate at 6.3V +/- 5%. Operating them for a short period of time at 7V won't be the end of the world. Extended operation at 7V will shorten their lifespan. Also, make sure that your transformer filament windings can support the current draw of the tube heaters (shouldn't be a problem for a preamp)
Download and play with PSUDII (power supply designer II) from Duncan amps if you haven't done so already; it is a very easy program to design the power supply with lots of rectifiers to choose from both tube and SS and full wave and center tapped. And best of all, it's free.
here is the link:
http://www.duncanamps.com/psud2/index.html
Another incredibly handy reference on Duncan's site is the tube data:
http://tdsl.duncanamps.com/tubesearch.php
Consider using a choke in place of R1; it will help ripple and is an easy way to drop volts without a big honkin' resistor.
If you seeing 7.1V out of your transformer filament windings with no load, that will drop somewhat to (hopefully) around 6.3V when powering the tube filaments, since you will be flowing current. If the voltage is still too high with everything connected up, you can add a small R (1 ohm or less) to get the filament voltage to 6.3V. The tube heaters are typically spec'd to operate at 6.3V +/- 5%. Operating them for a short period of time at 7V won't be the end of the world. Extended operation at 7V will shorten their lifespan. Also, make sure that your transformer filament windings can support the current draw of the tube heaters (shouldn't be a problem for a preamp)
Download and play with PSUDII (power supply designer II) from Duncan amps if you haven't done so already; it is a very easy program to design the power supply with lots of rectifiers to choose from both tube and SS and full wave and center tapped. And best of all, it's free.
here is the link:
http://www.duncanamps.com/psud2/index.html
Another incredibly handy reference on Duncan's site is the tube data:
http://tdsl.duncanamps.com/tubesearch.php
Consider using a choke in place of R1; it will help ripple and is an easy way to drop volts without a big honkin' resistor.
@Revintage
Thanks, I've laid out a new circuit using that cascade that you suggested. My unloaded voltage of 294V x 1.414 = 415V peak, so with that going into the power supply a load resistance of 10k ohms like you said gets 316V DC output. A resistance of 8500 ohms gets 301V DC.
Which resistor were you referring to when you said Rser?
@boywonder
Aren't chokes big and honkin' too? I'd use a choke if I had the room but I don't have access to a shop anymore so making big modifications to the chassis isn't an option, and theres not much room internally for extra parts.
Thanks, I've laid out a new circuit using that cascade that you suggested. My unloaded voltage of 294V x 1.414 = 415V peak, so with that going into the power supply a load resistance of 10k ohms like you said gets 316V DC output. A resistance of 8500 ohms gets 301V DC.
Which resistor were you referring to when you said Rser?
@boywonder
Aren't chokes big and honkin' too? I'd use a choke if I had the room but I don't have access to a shop anymore so making big modifications to the chassis isn't an option, and theres not much room internally for extra parts.
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