- Feb 16, 2008
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DIY Tube Preamp question
- Thread starter Bass4lyf
- Start date
I think I'm remembering the megaohm value for a bleeder resistor?
In any case, I've always thought the direct shorting method was kind of a harsh way to do things but I've heard it recommended so many times.... Is there times when this is more acceptable? i.e. is it the amount of capacitance or the voltage that pushes the limits here? (probably both)
In any case, I've always thought the direct shorting method was kind of a harsh way to do things but I've heard it recommended so many times.... Is there times when this is more acceptable? i.e. is it the amount of capacitance or the voltage that pushes the limits here? (probably both)
@OP
That looks like a nice kit for what i think to be a fair price. 6N3 (or 6N3P) are russian double triodes, similar to 12AX7 or ECC83 used in most commercial amps/preamps. I've worked with them and they're quite allright. The 220u/400v capacitors they seem to use are also ok, looks exactly like those I've installed years ago in a tube amp project and they're still going strong. The overall construction also seems good.
Now, a few things about building the project. The designer decided to use a double diode, tube rectifier for the power supply, which means that you'll have to use a 2x180V + 6.3V (or 180V 0 180V + 6.3V) transformer. The 2x180V section, after being rectified by the 6Z4, should give about +250V for the plate voltage of the two 6N3 tubes. The 6.3V section is for the heaters of the 6N3 and 6Z4 tubes. This basically means that the simplest solution is to buy the additional ~60 bucks transformer in order to make it work
The transformer that you have isn't a solution, I'm afraid 
Using a double diode instead of a bridge rectifier requires a "double-the-voltage" tap transformer instead.
Does all of the above sound weird? This means that you don't have experience building tube preamps/amps, which is absolutely ok; if you also don't have some experience in building any solid-state equipment, then you should stop for a while and try to read a bit about DIY solid-state and tube gear before diving in - 250 volts DC won't necessary kill you, but it's a hell of a ride
Good luck!!
Adrian
That looks like a nice kit for what i think to be a fair price. 6N3 (or 6N3P) are russian double triodes, similar to 12AX7 or ECC83 used in most commercial amps/preamps. I've worked with them and they're quite allright. The 220u/400v capacitors they seem to use are also ok, looks exactly like those I've installed years ago in a tube amp project and they're still going strong. The overall construction also seems good.
Now, a few things about building the project. The designer decided to use a double diode, tube rectifier for the power supply, which means that you'll have to use a 2x180V + 6.3V (or 180V 0 180V + 6.3V) transformer. The 2x180V section, after being rectified by the 6Z4, should give about +250V for the plate voltage of the two 6N3 tubes. The 6.3V section is for the heaters of the 6N3 and 6Z4 tubes. This basically means that the simplest solution is to buy the additional ~60 bucks transformer in order to make it work
The transformer that you have isn't a solution, I'm afraid Using a double diode instead of a bridge rectifier requires a "double-the-voltage" tap transformer instead.Does all of the above sound weird? This means that you don't have experience building tube preamps/amps, which is absolutely ok; if you also don't have some experience in building any solid-state equipment, then you should stop for a while and try to read a bit about DIY solid-state and tube gear before diving in - 250 volts DC won't necessary kill you, but it's a hell of a ride
Good luck!!
Adrian
should definatly never use a screwdriver aswell especially on anything bigger than a el84 single ended type amp, since you run the risk of shocking yourself and blowing chunks of the screw driver off.
+1
The Paia's are 12v wall wort with a 45v step up oscillator circuit.
Fairly safe. Still danger, soldering heat, fumes, caps wired backwards blowing up, etc.
There's really no benefit to learning electronics for education this way these days. You can pick up ltspice and model high voltage tube amp circuits safely. Even run .wav files through them.
See: http://www.duncanamps.com/technical/ltspice.html
Then you'd have a technology experience you could actually apply from ancient to modern circuits. No modern EE is going to design or redesign without a computer.
Now, a few things about building the project. The designer decided to use a double diode, tube rectifier for the power supply, which means that you'll have to use a 2x180V + 6.3V (or 180V 0 180V + 6.3V) transformer. The 2x180V section, after being rectified by the 6Z4, should give about +250V for the plate voltage of the two 6N3 tubes. The 6.3V section is for the heaters of the 6N3 and 6Z4 tubes. This basically means that the simplest solution is to buy the additional ~60 bucks transformer in order to make it work
This does make sense to me, and i do understand what everyone else is saying about me being in danger because of my poor knowledge on tube preamps. I think I will go and buy a book or two and do some severe reading. The reason why Im interested in buying that second tube preamp kit that I linked yas (the stereo marantz one) is because it all comes assembled, except for the transformer and any other things I would want to add. I just want you guys to tell me if that preamp would be adequate enough as a 2 channel guitar/bassguitar preamp, just so I can get a start with what I want to do with the preamp. I have worked 'alittle' with solidstate amps, but I am always building speakers. Before I started building speakers, I new nothing, but then I did my research, learnt how to work with crossovers, and began to build speakers. And in my opinion, these speakers have come out real nice. Now I want to try something different, something alittle more complex, and that is the tube preamp. I know I have no knowledge about them now, but when it comes time to actually building it, I most likely will have. I have only just started my 'learning' of the tube preamp hence all these dumb questions on this forum. But you gotta start somewhere.
I really appreciate the help from everyone in this forum anyhow, no matter how harsh it was.
Hi
Not having the schematic for that kit, I'm not able to tell you anything specific on how appropriate would be for a instrument preamp. However, by the looks of it, seems like pretty much the typical configuration, so there's no reason why it wouldn't work for you.
For some reading on DIY with tubes, visit Invalid Link Removed , there's a lot of nice stuff there.
Break yer leg!
Adrian
Not having the schematic for that kit, I'm not able to tell you anything specific on how appropriate would be for a instrument preamp. However, by the looks of it, seems like pretty much the typical configuration, so there's no reason why it wouldn't work for you.
For some reading on DIY with tubes, visit Invalid Link Removed , there's a lot of nice stuff there.
Break yer leg!
Adrian
Actually there seems to be some confusion over what this tube actually is. It would have to be a triode in order to act as even a buffer but some data sheets show the tube as a rectifier or diode!
Paul
http://www.ax84.com/
Read through here.
I know plenty of small time amp builders who started out there.
Educate yourself!
P.S. I got my start building a 100w Superbass off of weber.... but i had an EE breathing down my neck. Even then it took me 40 hours plus to get it right! That doesnt include the other uncoutable hours of reading ETC.
Read through here.
I know plenty of small time amp builders who started out there.
Educate yourself!
P.S. I got my start building a 100w Superbass off of weber.... but i had an EE breathing down my neck. Even then it took me 40 hours plus to get it right! That doesnt include the other uncoutable hours of reading ETC.
@Bass4lyf:
There's usually no need for a voltage regulator in a preamp, so you can safely go without one. You would use one if, for example, you'd want the preamp gain to be something constant, not being influenced by the occasional power supply voltage variations.
@BassmanPaul:
Hm, weird. 6n3p (and 6N2P) are definitely double triodes, in fact, 6N2P would be more suitable for a drop-in replacement for 12AX7, being also pin compatible. 6N3P has a different pin-out and the heater is 6.3V only.
Regards,
Adrian
There's usually no need for a voltage regulator in a preamp, so you can safely go without one. You would use one if, for example, you'd want the preamp gain to be something constant, not being influenced by the occasional power supply voltage variations.
@BassmanPaul:
Hm, weird. 6n3p (and 6N2P) are definitely double triodes, in fact, 6N2P would be more suitable for a drop-in replacement for 12AX7, being also pin compatible. 6N3P has a different pin-out and the heater is 6.3V only.
Regards,
Adrian
Algernon it could be that there is more information on Russian tubes available in Europe than in the Americas.
The listing does mention that the board is a shunt regulated push pull configuration so that gives the schematic. That would indicate more of a buffer than a pure amplifying stage.
Paul
The listing does mention that the board is a shunt regulated push pull configuration so that gives the schematic. That would indicate more of a buffer than a pure amplifying stage.
Paul
I was just glancing through my tube amp book and im pretty sure it said that the power transformer puts out voltage in AC, but the tubes need DC voltage to power them. Is that right? If so, does this mean Il need to have some sort of rectifying happening between the tubes and power transformer to switch the voltage to DC? Will I need something like this - http://cgi.ebay.com.au/Tube-Rectifi...pt=Vintage_Electronics_R2&hash=item483a4bfd9b
or is there a simple small circuit I can put together using a few diodes and stuff?
Because of the technicality of tube preamps, I decided to buy an already built stereo tube preamp pcb board, with all the components soldered on. So I just need to add a power source, in/out jacks, tubes and whatever pots I want/need. If you guys need/want to see the schematics of this preamp, Il put em up.
or is there a simple small circuit I can put together using a few diodes and stuff?
Because of the technicality of tube preamps, I decided to buy an already built stereo tube preamp pcb board, with all the components soldered on. So I just need to add a power source, in/out jacks, tubes and whatever pots I want/need. If you guys need/want to see the schematics of this preamp, Il put em up.
Bass4lyf - sit down and study this schematic until you know how it works. That's what I did 20 years ago.
Invalid Link Removed
And yeah, you have to rectify the AC power supply voltage to DC, then filter it so you have DC to power the tubes. The tubes act like a variable resistor controlled by the voltage on the grid, so they are essetially modulating the DC that's feeding them. Capacitors pass AC, but block DC. These are just a few of the things you need to understand to get into building tube amps. Do a lot of research to figure out what you're doing.
Chris
Invalid Link Removed
And yeah, you have to rectify the AC power supply voltage to DC, then filter it so you have DC to power the tubes. The tubes act like a variable resistor controlled by the voltage on the grid, so they are essetially modulating the DC that's feeding them. Capacitors pass AC, but block DC. These are just a few of the things you need to understand to get into building tube amps. Do a lot of research to figure out what you're doing.
Chris
Well - at least he's not playing with flybacks and H/KV power supplies, although anything over 80V is considered 'high voltage' any more to satisfy those in Lawyer Land.
For interest I purchased the kit via Ebay. It is not a kit per se but two pre-assembled boards, one for power and the other for the pre-amp. It IS nicely put together but no schematic is provided. Apparently the factory will not provide the seller with a copy. The ad is a little misleading in that I read send $54 if you want the power transformer. The seller meant send an additional $54 for the transformer.
When I get the time I'll sketch out the schematic.
Paul
When I get the time I'll sketch out the schematic.
Paul
First - do heed the warnings about the hazardous voltages required for (most) tube circuits!
Second - basic tube circuits are easy to understand and design.
To get started you don't need an EE degree, just a few basic concepts and very elementary algebra. Voltage, current, resistance, V=IR (Ohm's law), P=IV (power), capacitance and inductance. Then understand that (to a first approximation) a tube uses a small voltage input to control current, and you've got a basic toolkit to understand and design simple tube circuits.
There is a wealth of information available on the web to help relate these simple concepts to tubes. Here are just few sites I've found:
How To Design Valve Guitar Amplifiers - oh, yes, in the UK, what we call "toobs" they call "valves".
tubebooks.org - "Vintage info from the days of vacuum tubes".
John Broskie's Guide to Tube Circuit Analysis & Design - Okay, this one is more advanced, and more oriented towards high-quality audio, but once you understand the basics, this will blow your mind!
Second - basic tube circuits are easy to understand and design.
To get started you don't need an EE degree, just a few basic concepts and very elementary algebra. Voltage, current, resistance, V=IR (Ohm's law), P=IV (power), capacitance and inductance. Then understand that (to a first approximation) a tube uses a small voltage input to control current, and you've got a basic toolkit to understand and design simple tube circuits.
There is a wealth of information available on the web to help relate these simple concepts to tubes. Here are just few sites I've found:
How To Design Valve Guitar Amplifiers - oh, yes, in the UK, what we call "toobs" they call "valves".
tubebooks.org - "Vintage info from the days of vacuum tubes".
John Broskie's Guide to Tube Circuit Analysis & Design - Okay, this one is more advanced, and more oriented towards high-quality audio, but once you understand the basics, this will blow your mind!
A couple week s ago I purchased the "Inside Tube Amps" book by Dan Torres, almost finished reading it. I must say it is a bloody good book, it has taught me alot. I was just looking over my earlier posts in this thread and cant believe how ridiculous I sounded. I do understand that reading one book wont make me know everything needed to know about how tube amps work, but I do feel I have a fairly acceptable idea on the very basics of how they work and what is required to build one. I must apologise for asking such dumb questions in this thread a few weeks ago. Im not saying that I wont be asking anymore dumb questions but il try my best not to.
Anyway, I purchased this already built pcb board and recieved it in the mail yesterday. http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=310202133571&ssPageName=STRK:MEWAX:IT
It came with schematics, here it is (hope its big enough to read):
It says it needs 280v DC to power the tubes and another 12.6v DC. I just want to make sure Im on the right track with this. The power transformer will put out voltage in AC, I will need to convert this to DC for the tubes using a bridge rectifier. According to Dan Torres' 'Inside Tube Amps' book, a bridge rectifier boosts the rectified voltage 1.4x the ac voltage from the trans. In order to find the correct trans for my preamp, I need to divide 280v by 1.4 which is 200v right? So this means Il need a transformer that puts out 200 volts. But Im unsure of this, do I need a transformer that is 200-0-200, or 100-0-100? Also, for the 12.6v, Im assuming that I will have to bridge rectify this aswell? 12.6 divided by 1.4 equals 9 volts. So I need a transformer that has a 200v tap and a 9 v tap? Is that how they work?
Anyway, I purchased this already built pcb board and recieved it in the mail yesterday. http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=310202133571&ssPageName=STRK:MEWAX:IT
It came with schematics, here it is (hope its big enough to read):
It says it needs 280v DC to power the tubes and another 12.6v DC. I just want to make sure Im on the right track with this. The power transformer will put out voltage in AC, I will need to convert this to DC for the tubes using a bridge rectifier. According to Dan Torres' 'Inside Tube Amps' book, a bridge rectifier boosts the rectified voltage 1.4x the ac voltage from the trans. In order to find the correct trans for my preamp, I need to divide 280v by 1.4 which is 200v right? So this means Il need a transformer that puts out 200 volts. But Im unsure of this, do I need a transformer that is 200-0-200, or 100-0-100? Also, for the 12.6v, Im assuming that I will have to bridge rectify this aswell? 12.6 divided by 1.4 equals 9 volts. So I need a transformer that has a 200v tap and a 9 v tap? Is that how they work?
Your math is pretty much correct. If you are going to be using a full wave bridge rectifier, your high voltage winding should be 200-200 (there's no need fo the 0V center tap), or 100-0-100, but make sure you don't connect the 0V tap to ground if you use a 100-0-100 with a full wave bridge. For power supply filter capacitor, you'll only need 20uF or so, but to smooth it even more, you'll probably want to use a couple of 20uF/350V caps separated by a 100 ohm/5W resistor (pi filter since it looks like the letter "pi"). You don't have to DC rectify the 12.6V, but you can if you want. If you want the simplest solutin, you can feed the 12.6V with AC since it's just the heaters for the tubes. In that case you'd need a power transformer with 200V 20mA winding, 12.6V 0.5A winding, and whatever primary voltage you need (if your in the Sydney, I think you guys use 230VAC from the wall, right?)
Chris
Chris
