Hello!
Before actually getting to soldering, i thought it's a good idea to get some opinions on this scheme, you know, what's all the mistakes etc. Casual stuff.
The 3 1MEG resistor's should in reality be pots, though i didn't find any pots in LTSpice. And 2 560ohm are trimpots for biasing.
Simulation was taken from the grids of both output tubes.
Also 1 question a bit out of this: Is under 3-band EQ also meant Volume, Treble, Bass? If not, how to do 3-band EQ with tubes?
Before actually getting to soldering, i thought it's a good idea to get some opinions on this scheme, you know, what's all the mistakes etc. Casual stuff.
The 3 1MEG resistor's should in reality be pots, though i didn't find any pots in LTSpice. And 2 560ohm are trimpots for biasing.
Simulation was taken from the grids of both output tubes.
Also 1 question a bit out of this: Is under 3-band EQ also meant Volume, Treble, Bass? If not, how to do 3-band EQ with tubes?
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Would be more enlightening if you take the waveform from the cathodes or the anodes of the output tubes, to see at which point they go into cutoff (meaning they go into class-b). If they do not, it means your proposed amplifier is class-a.
The waveform looks distorted, it is because you have the EQ, but of course you want to have this, it is not for Hi-Fi!
3-band EQ, means Treble - Middle - Bass (TMB), almost all Fenders have it. Before it, you can have the Volume control.
The waveform looks distorted, it is because you have the EQ, but of course you want to have this, it is not for Hi-Fi!
3-band EQ, means Treble - Middle - Bass (TMB), almost all Fenders have it. Before it, you can have the Volume control.
Hi.
It looks like you are using much too large a plate resistor on the input stage. that 6dj8 will be running at less than a milliamp. barely turned on. 100k is typical load for a 12ax7. 100 volts seems pretty low for supply voltage as well. I know you want distortion, but that waveform looks grossly distorted.
I used 6dj8's for my guitar amp too. here is what I built. the bottom of the volume control in front of the phase splitter should be connected to ground though
It looks like you are using much too large a plate resistor on the input stage. that 6dj8 will be running at less than a milliamp. barely turned on. 100k is typical load for a 12ax7. 100 volts seems pretty low for supply voltage as well. I know you want distortion, but that waveform looks grossly distorted.
I used 6dj8's for my guitar amp too. here is what I built. the bottom of the volume control in front of the phase splitter should be connected to ground though
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With 560Ohms for the cathodes of the 6V6s you are going to be running pretty cool at around 20-22mA. You will probably run class AB1 with a 270V supply.
I recommend dropping down to a 330 or 300Ohm resistor to get the current closer to what the data sheet calls out for 250V B+ (45mA at -12.5V on the grid).
I recommend dropping down to a 330 or 300Ohm resistor to get the current closer to what the data sheet calls out for 250V B+ (45mA at -12.5V on the grid).
By the way, if you are going to use 6P1P-EV tubes instead of the 6V6 shown in the schematic, I built a high gain lead amp with them along with 6P2P-EVs for gain stages and phase splitter.
I've built two similar amps with one running Class A at 250V B+ putting out 8W and a second one running class AB1 at 325V B+ putting out over 10W.
http://www.diyaudio.com/forums/tubes-valves/184371-volume-control-tonestacks-potentiometers-noise.html
I've built two similar amps with one running Class A at 250V B+ putting out 8W and a second one running class AB1 at 325V B+ putting out over 10W.
http://www.diyaudio.com/forums/tubes-valves/184371-volume-control-tonestacks-potentiometers-noise.html
There's 2 major mistakes in that schem Tauri, that will stop it from working. I suggest you copy known good schematics until you gain an understanding of how tubes work. Look at schematics that work that are similar to yours, and look for the differences, that will be what stops yours from working.
Some missing connections and coupling caps in there. I simulate pots as two resistors with a connection in between them. That way I can change the value of the two resistors and rerun the simulation to get different levels. I am sure there is a better way but so far does what I need. Plotting the current through L1 and L2 in the transient simulation mode will tell you a lot about your operating mode.
Thanks for pointing that out. Corrected my scheme a bit.
So, few guys are on it already, what am I missing now?
Also is it better to connect triodes in series like in rman's scheme? Does it give more gain?
And actually I do use 6p1p-EV's in the output, thus needed to lower the voltage.
So, few guys are on it already, what am I missing now?
Also is it better to connect triodes in series like in rman's scheme? Does it give more gain?
And actually I do use 6p1p-EV's in the output, thus needed to lower the voltage.
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A few thoughts. Your cathodyne phase splitter has no bias, you need a grid leak resistor to the bottom of R10. Also I doubt the need for a bypass capacitor on that bias resistor.
Unless you are looking for clean only I don't think that the 6DJ8s are going to give you nearly enough gain. A couple of 12AX7 or 12AY7 stages would be more normative for a guitar. The high mu triodes have rather high rp though so a cathode follower is often used to drive the tone stack. Also cathodyne PI will have different sound at overdrive than the LTP such as used in Marshalls.
Unless you are looking for clean only I don't think that the 6DJ8s are going to give you nearly enough gain. A couple of 12AX7 or 12AY7 stages would be more normative for a guitar. The high mu triodes have rather high rp though so a cathode follower is often used to drive the tone stack. Also cathodyne PI will have different sound at overdrive than the LTP such as used in Marshalls.
Hi all.
Mike: Good catch on that missing grid resistor. I was going to say his circuit should work now. Interesting comment about the cathodyne as compared to the LTP. I had no idea as this was my first guitar amp, built or bought.
Tauri : The tubes in series as you say in my circuit are called a cascode. It is a high gain stage like you guessed. I did it that way because as Mike says 6dj8's don't have that much gain. That is also why I added a bypass switch around the tone stack which looses most of the gain from the first stage.
Cheers.
Rolf.
Mike: Good catch on that missing grid resistor. I was going to say his circuit should work now. Interesting comment about the cathodyne as compared to the LTP. I had no idea as this was my first guitar amp, built or bought.
Tauri : The tubes in series as you say in my circuit are called a cascode. It is a high gain stage like you guessed. I did it that way because as Mike says 6dj8's don't have that much gain. That is also why I added a bypass switch around the tone stack which looses most of the gain from the first stage.
Cheers.
Rolf.
Rman, on yours you might consider changing the cascode to a mu follower and putting the tone stack after the mu follower which has better drive and lower zout than the common cathode gain stage. Another thing to consider is that at least with the mu follower and I think also with cascode the over load characteristics are a lot more abrupt than with common cathode gain stages so you may find the distortion a bit nasty (my be what you want though).
K1 L1 L2 L3 1
Don't use leading dot at the beginning, I don't know why...
You are also gonna have to guess some inductor values
and provide a load resistor.
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Mike:
Interesting thoughts. There is a fine line on the gain control between "crunch" and a big mess. I originally tried the cascode first where it wouldn't get overloaded but it couldn't drive the tone stack. I don't really feel like rebuilding it right now, but I will keep it in mind.
Thanks.
Rolf.
Interesting thoughts. There is a fine line on the gain control between "crunch" and a big mess. I originally tried the cascode first where it wouldn't get overloaded but it couldn't drive the tone stack. I don't really feel like rebuilding it right now, but I will keep it in mind.
Thanks.
Rolf.
Are you using 6N1P and referencing 6DJ8 in your schematic since you are actually using 6P1Pand using 6V6 symbols?
You have one spare triode not shown on the schematic. Convert your Cathodyne to a LTP and you will gain some gain as a side benefit.
If you are using Svetlana 6P1P-EVs don't worry about the 250V limit. I run them at 325V and have no problems. Just keep the screen voltage down at 250 or less and watch your anode dissipation. Keep your anode dissipation below the 12W limit and you will be fine.
In experiments I have cranked 6P1P-EVs over 375V on the anodes for short periods (IIRC) with no apparent long term problems. One of these days I'm going to build an amp to do long term testing at 350V AB1 to see how they do.
You don't need (or want) polarized caps as coupling caps.
You have one spare triode not shown on the schematic. Convert your Cathodyne to a LTP and you will gain some gain as a side benefit.
If you are using Svetlana 6P1P-EVs don't worry about the 250V limit. I run them at 325V and have no problems. Just keep the screen voltage down at 250 or less and watch your anode dissipation. Keep your anode dissipation below the 12W limit and you will be fine.
In experiments I have cranked 6P1P-EVs over 375V on the anodes for short periods (IIRC) with no apparent long term problems. One of these days I'm going to build an amp to do long term testing at 350V AB1 to see how they do.
You don't need (or want) polarized caps as coupling caps.
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@TheGimp: No, I do use 6DJ8's for this preamp. I think i'm going to leave it as cathodyne, because I don't want that much gain, though with 6DJ8's there is very little compared to 12AX7.
If they can run on so much higher anode voltage, why isn't it marked on the datasheet? Anyhow, I can't get higher than +270V with my transformer, so have to settle.
If they can run on so much higher anode voltage, why isn't it marked on the datasheet? Anyhow, I can't get higher than +270V with my transformer, so have to settle.
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