Yes you need to know the voltage. I guess I should have said "You need to draw many load lines." So you draw a load line best on the rule of thumb of using 10X larger resistors and see if you like the result. If not draw an other using a different voltage and so on.
Design, even when done by professional engineers is never a direct process. It is always interactive. You never know if you over-all idea is good until you work out the next level of details and then most of the time you go back. Designing houses, software and amps is all the same type of interactive cycle.
That's why guitar amps have gain controls. I assume your amp does and most you see sold in stores do have at least one gain control pot. The control pot does not really control gain. A triode stage has what gain it has. The pot acts as an attenuator.
and when you turn up the gain the distortion sound is because you have overloaded the NEXT stage. The first triode in a guitar amp is always "clean" almost HiFi but needs to have enough gain that if no atenuated it would drive the nest stage to square wave clipping. Then the gain knob control if that next stage is over driven or not
So for a clean kind of sound you lower the gain and raise the master volume but if some kind of clipping "fuzz" sound is wanted you set the gain to ten but then it is to loud so you turn down the master volume. I'm sure you know this. some amps have two gain stages and two gain control knobs. The gain of the triode stage determines the effect when the control is at 10.
But you can modify the preamp's gain later by swapping out the plate load resistor. That is one reason I like buillding with turret boadrd, resistors can be swapped out in seconds, just heat the turret and the part comes lose with cutting or untwisting of wire leads. I've also used resistor substitution boxes and flipped the switch and gone with what sounds best. You need 20 years of experience to just know what's best from the start, few people ever build enough amps to learn that. So like I said expect to have to change things at every stage.
Or you could just make an exact clone of an amp you like.
ok thank you very much! I guess my real issue then is that I'm trying to figure out what kind of voltage im looking for for the power transformer. I realize that if worst comes to worst i can sort of dial in a voltage using a trimmer pot or resistors, but I want to get in the ballpark before i start playing around with resistors. Thank you for your help. I was definitely getting too wrapped up in figuring out values according to numbers rather than sound.
is the voltage applied to the center tap on the OP trafo important? I'm have a hard time figuring out why its there. is it just the largest voltage available?
is the voltage applied to the center tap on the OP trafo important? I'm have a hard time figuring out why its there. is it just the largest voltage available?
Yes, the voltage on the OT CT is important.....
The voltage on the OP transformer center tap is what the anodes of the output tubes see. As a basic rule of thumb, you need to keep the anode current and voltage within the power dissipation specs of the chosen output tube. For output triodes, the current times the anode voltage determine the power dissipation. For pentodes, the screen grids also come into play a bit as well. If you exceed the power dissipation of the output tubes, bad things can happen, like shorted tube life, melted plates, shorted tubes and smoked parts. Some designs exceed the ratings with varying results. Also keep in mind that as B+ exceeds 450-500V or so, your choices of power supply caps with sufficient voltage ratings starts to get small. You can always stack lower voltage rated caps if needed....
Take a look at Duncan amps TDSL pages for typical operating conditions for various output tubes. The link below is for a 6V6 output tube. The table shows typical operating conditions with a given B+, load, bias, distortion, power output, etc for both single ended (SE) and push pull (PP) operation.
TDSL Tube data [6V6]
If you can understand and digest that data in the tables, that will go a long way to a successful amp design.
If you end up needing to reduce power supply volts there are several ways of doing that that are more efficient than just adding series resistance, such as using a CLC supply and a small first cap value, etc.
The voltage on the OP transformer center tap is what the anodes of the output tubes see. As a basic rule of thumb, you need to keep the anode current and voltage within the power dissipation specs of the chosen output tube. For output triodes, the current times the anode voltage determine the power dissipation. For pentodes, the screen grids also come into play a bit as well. If you exceed the power dissipation of the output tubes, bad things can happen, like shorted tube life, melted plates, shorted tubes and smoked parts. Some designs exceed the ratings with varying results. Also keep in mind that as B+ exceeds 450-500V or so, your choices of power supply caps with sufficient voltage ratings starts to get small. You can always stack lower voltage rated caps if needed....
Take a look at Duncan amps TDSL pages for typical operating conditions for various output tubes. The link below is for a 6V6 output tube. The table shows typical operating conditions with a given B+, load, bias, distortion, power output, etc for both single ended (SE) and push pull (PP) operation.
TDSL Tube data [6V6]
If you can understand and digest that data in the tables, that will go a long way to a successful amp design.
If you end up needing to reduce power supply volts there are several ways of doing that that are more efficient than just adding series resistance, such as using a CLC supply and a small first cap value, etc.
thats exactly what i was looking for thank you...it makes sense now that i really think about it...I assume all of these voltages are with respect to the cathode correct?
They are with respect to ground, so if you are using cathode bias, the voltage drop across the cathode R subtracts from the B+ to calculate the drop across the tube. That's why fixed bias yields a little more output power for a given B+ than cathode bias, since the cathode is grounded, and all the drop is across the tube.
Champ Amp
Reading this thread has been very interesting from several aspects, and I thank everyone that posted to it.
Although I am not a pro at the engineering side of things, I have made several amps in my time, and am actually beginning on a Class A project very soon. However, that is a HiFi amp, not a guitar amp.
However, as an old-time audiophile as well as both a guitar and bass player, there are a couple of things that I would like to add.
A couple of the posts recommended that you consider using a known design to begin with, and that you consider the Fender Champ as a starting place. I highly recommend that you seriously consider this, assuming that you do not need high SPL. In my younger days, I was a recording engineer, and while multiple Marshall stacks are great, unless you need all that power to fill a large space, you will not need it. In terms of sound, the Fender Champ is hard to beat. Erik Clapton used a Champ to record the Layla album. It has to do with the tone of the amp/speaker combo and how that amp overdrives when pushed.
I noted that you made the choice to go with all tubes, which would have been my other recomendation. It is difficult to get a SS circuit to go into the type of distortion that a guitar player wants. There is an edgyness about it that just doesn't work for most guitar use.
As to the tubes, the reason that most guitar amps use the 6V6 and similar as opposed to the KT88 types is once again associated with how they go into distortion. However, they will not provide the higher power levels that the KT 88's will.
In my home HiFi system, I use a tube pre (Marantz 7C) with a pair of modified Dyna Mk III's to drive the electrostatic tweeters, but two different SS amps to drive the midrange boxes (Braun 810's) and the sub (RH Lab 1). When I was playing, I used a tube setup for my guitar, but a SS for my bass playing as the SS gives a tighter bottom.
Think about the Champ for a first project, then if you need more power to go over the rhythm section and brass, then perhaps something along the lines of a Twin Reverb. Later, if you wind up doing stage gigs, perhaps a high power amp will be needed and you can think about a Marshall type circuit.
After you have gotten the tube thing working and played around with it, and you want to really step up, you might think about looking into a Class A amp. There are a number of very good guitar Class A amps being made now (both tube and SS designs), but they require a lot of cooling as their power goes up, and are very-very inefficient in terms of power consumption for power output. However, a little bit of Class A power equates to a lot of Class AB power.
Best of luck with your project.
Lilith
"Life, don't talk to me about life..." Marvin the Robot, Hitchhikers Guide to the Galaxy
Reading this thread has been very interesting from several aspects, and I thank everyone that posted to it.
Although I am not a pro at the engineering side of things, I have made several amps in my time, and am actually beginning on a Class A project very soon. However, that is a HiFi amp, not a guitar amp.
However, as an old-time audiophile as well as both a guitar and bass player, there are a couple of things that I would like to add.
A couple of the posts recommended that you consider using a known design to begin with, and that you consider the Fender Champ as a starting place. I highly recommend that you seriously consider this, assuming that you do not need high SPL. In my younger days, I was a recording engineer, and while multiple Marshall stacks are great, unless you need all that power to fill a large space, you will not need it. In terms of sound, the Fender Champ is hard to beat. Erik Clapton used a Champ to record the Layla album. It has to do with the tone of the amp/speaker combo and how that amp overdrives when pushed.
I noted that you made the choice to go with all tubes, which would have been my other recomendation. It is difficult to get a SS circuit to go into the type of distortion that a guitar player wants. There is an edgyness about it that just doesn't work for most guitar use.
As to the tubes, the reason that most guitar amps use the 6V6 and similar as opposed to the KT88 types is once again associated with how they go into distortion. However, they will not provide the higher power levels that the KT 88's will.
In my home HiFi system, I use a tube pre (Marantz 7C) with a pair of modified Dyna Mk III's to drive the electrostatic tweeters, but two different SS amps to drive the midrange boxes (Braun 810's) and the sub (RH Lab 1). When I was playing, I used a tube setup for my guitar, but a SS for my bass playing as the SS gives a tighter bottom.
Think about the Champ for a first project, then if you need more power to go over the rhythm section and brass, then perhaps something along the lines of a Twin Reverb. Later, if you wind up doing stage gigs, perhaps a high power amp will be needed and you can think about a Marshall type circuit.
After you have gotten the tube thing working and played around with it, and you want to really step up, you might think about looking into a Class A amp. There are a number of very good guitar Class A amps being made now (both tube and SS designs), but they require a lot of cooling as their power goes up, and are very-very inefficient in terms of power consumption for power output. However, a little bit of Class A power equates to a lot of Class AB power.
Best of luck with your project.
Lilith
"Life, don't talk to me about life..." Marvin the Robot, Hitchhikers Guide to the Galaxy
Thank you for you input lilith. looking at the fender champ, it looks really simple and easy. (possibly I'll buy enough tubes to make that and a plexi-style amp) This way I can just make a carbon copy of the champ and get used to playing around with tubes and focus on the plexi from a more design based standpoint (including a few custom mods). I do have 2 speakers, both of which are rated way higher then i need.
Also, boywonder, I was asking about the values on the datasheet (i dont know if that was clear) and i was asking mainly because the grid voltage ratings are all negative, and since I dont have any negative voltages on this amp, I was wondering how i would get anywhere near that.
the datasheets (EH GE) for 6v6 says the maximum power dissipation is 14W, does that mean a PP can give me 28W or is taking PP into consideration? To me, it seems like the GE one means that 14W total for both tubes where as the EH one looks like its just for 1 tube. Is this a difference in tubes or am i reading one of the datasheets wrong?
Also, boywonder, I was asking about the values on the datasheet (i dont know if that was clear) and i was asking mainly because the grid voltage ratings are all negative, and since I dont have any negative voltages on this amp, I was wondering how i would get anywhere near that.
the datasheets (EH GE) for 6v6 says the maximum power dissipation is 14W, does that mean a PP can give me 28W or is taking PP into consideration? To me, it seems like the GE one means that 14W total for both tubes where as the EH one looks like its just for 1 tube. Is this a difference in tubes or am i reading one of the datasheets wrong?
Yes, the grid voltage needs to be negative with respect to the cathode, sorry.....
As you've probably already figured out, you typically get the grid voltage below the cathode voltage one of two ways: Cathode bias, where the voltage drop across the cathode R raises the voltage at the cathode above the grid voltage by the req'd amount, or fixed bias where the cathode is grounded and you supply an adjustable -ve voltage to the grid.
You may be confusing dissipation power with output power......The max dissipation power is the max power (volts times current) that the tube will take before the plates (anodes) glow red and/or other bad things happen. Output power to the speakers is less than that, in triode mode, way less. Looking at the Duncan amps page PaMax (Power anode max) is the max dissipation power and Pout is the output power.
It appears that driving the tubes hard in pentode mode AB1 push pull will yield a max output power of 14W. This data is the second to last data set in Duncan's table and corresponds to the GE data. It's the data set with an anode voltage of 285V and an 8K output transformer at 70ma idle.
Last edited:
ok. I understand how to make the cathode voltage higher, but it sounds like you suggest keeping the cathode connected to ground, so how do i make a negative power supply without giving up half of my voltage in my power supply?
and yes. I realized my mistake mixing up dissipation and output power almost immediately after posting. thank you. so just for clarification...that means that 2 6v6's in an AB PP setup will output 14W total correct?
and yes. I realized my mistake mixing up dissipation and output power almost immediately after posting. thank you. so just for clarification...that means that 2 6v6's in an AB PP setup will output 14W total correct?
I'm not suggesting fixed bias.......it makes for a more complex power supply, and requires periodic adjustment. Cathode bias works just fine, and is a little simpler. For a first build, it may be wise to stick with cathode bias.
2 6V6's in AB1 pentode PP will output 14W or less. Look at the other data sets at Duncan's site. They'll output about 6W in triode, and somewhere in between 6-14W wired as ultralinear, probably around 10-11W as a guess. Don't get too hung up on output power, if you want good guitar distortion, lower power may be more useful.
If you want more power, you can use EL34 tubes or 6L6 tubes, etc.
yea i want to keep the voltages relatively low for this project, so im not particularly worried about the power, but i just wanted to make sure the trafo i was looking at would work. I think im ready to start ordering parts (the only thing is still have to figure out is power transformer)...i think
while im at it, does anyone have suggestions for what brands of tubes are good or bad? I'm thinking about going with an edcor op trafo. what do you guys think?
also, Ive read that using a matched pair for the PP output stage diminishes 2nd order harmonics and accentuates 3rd order, which is apparently undesireable. Do you guys use matched pairs for your PP outputs?
also, Ive read that using a matched pair for the PP output stage diminishes 2nd order harmonics and accentuates 3rd order, which is apparently undesireable. Do you guys use matched pairs for your PP outputs?
Last edited:
Edcor transformers are a good value and sound great. They do have a lead time that's typically 4-6 weeks.....so keep that in mind.
I imagine that you have already checked out Edcor's PP offerings; if you haven't, they have the XPP series ($), GXPP series ($$), and CXPP series ($$$). The XPP series are naked (no ene bells); the others have end bells, most likely not important for a MI amp.
You'll probably want to use a XPP or GXPP series transformer for a guitar amp. While you are at it, you may want to order a power transformer from them also.
A you building a champ clone or something else? Have you ironed out all of your component values?
Can you post your intended schematic?
Also, consider downloading Duncan's free power supply designer II (PSUDII) software. It'll help tremendously in designing a SS or tube rectified power supply, and you can easily evaluate B+ sag, etc for a given transformer, etc.
http://www.duncanamps.com/psud2/index.html
I imagine that you have already checked out Edcor's PP offerings; if you haven't, they have the XPP series ($), GXPP series ($$), and CXPP series ($$$). The XPP series are naked (no ene bells); the others have end bells, most likely not important for a MI amp.
You'll probably want to use a XPP or GXPP series transformer for a guitar amp. While you are at it, you may want to order a power transformer from them also.
A you building a champ clone or something else? Have you ironed out all of your component values?
Can you post your intended schematic?
Also, consider downloading Duncan's free power supply designer II (PSUDII) software. It'll help tremendously in designing a SS or tube rectified power supply, and you can easily evaluate B+ sag, etc for a given transformer, etc.
http://www.duncanamps.com/psud2/index.html
Last edited:
Not sure if anyone has pointed you to the AX84 web site. AX84.com - The Cooperative Tube Guitar Amp Project I have built a few tube amps, but only one tube guitar amp. I used a pre and power amp from the building blocks section of the AX84 site. Just had a quick look, I built a 20 watt 6V6 PP amp, but it looks like it has been replaced by a 50 watt PP EL34. The great thing about the site is that it has templates for turret boards and for chassis drilling and great wiring diagrams. It really helps with the layout. Even if you don't use one of their designs, I would suggest checking the site out to modify their layout diagrams etc to suit what you eventually build.
Good luck with he project!
Good luck with he project!
I think im going to order enough tubes for a fender champ and something based on Mark Huss's plexi 6v6. for the champ im just going to try to copy a schematic exactly (Probably this one) and see if i can build and debug it correctly. and if that works out, then I will build the plexi-ish, because i really like having those 2 channels...I have 2 speakers, so that wont be a problem...ill have to figure out things like trafos for the champ though.
I can post a schematic of what im thinking for the plexi when i get home tonight. which reminds me, what do you guys use to draw up schematics? i've been using eagle recently, but its kind of annoying in some respects
thank you for that program! that is awesome. also, I have been directed to AX84...awesome site for this kind of thing!
I can post a schematic of what im thinking for the plexi when i get home tonight. which reminds me, what do you guys use to draw up schematics? i've been using eagle recently, but its kind of annoying in some respects
thank you for that program! that is awesome. also, I have been directed to AX84...awesome site for this kind of thing!
Last edited:
Hey, so I've been looking at power trafos, and it seems like it would be more economical to use a tube with a 6.3v heater, rather than the 5Y3, 5 v in the champ rectifier (also, i'm kind of confused by the heater/cathode situation). Does anyone have suggestions for good rectifier tubes with a 6.3 v heater supply?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.