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Tauri 14th April 2011 06:48 PM

6P1P-EV PP guitar amp tryout.
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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?

costis_n 14th April 2011 08:19 PM

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.

rman 15th April 2011 01:31 AM

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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 [B]grossly[B] 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

TheGimp 15th April 2011 03:14 AM

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).

TheGimp 15th April 2011 03:51 AM

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.

Ian444 16th April 2011 11:17 AM

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.

rman 17th April 2011 05:43 PM

Ian is right. Let's give another clue. The first is a missing essential part. The second is something connected wrong.

costis_n 17th April 2011 06:14 PM

One misconnected, one not connected at all. Also no gridstoppers. Makes one wonder about the usefulness of simulation software...

mashaffer 17th April 2011 06:42 PM

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.

Tauri 17th April 2011 06:47 PM

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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.
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