I am building a valve amplifier, single ended, no feedback, triode-connected 7591S amplifier. For driver valve I am using one 6SN7. The schematic I am planning to use is based on Mikael Abdellah's KT88 amplifier and looks like this:
But I am unsure about the values on most components.
The things that are fixed: the tubes, output transformer and B+. Everything else is subject to change.
Thoughts? Tips? 🙂
But I am unsure about the values on most components.
The things that are fixed: the tubes, output transformer and B+. Everything else is subject to change.
Thoughts? Tips? 🙂
You will get about 40mA with 16V bias, and 344V plate to cathode. 344 + 16 = 360V B+. There is some drop of B+ through the primary DCR.
16V / 0.04A = 400 Ohms. Start with a self bias resistor of 390 Ohms, and adjust as necessary to get 40mA.
For some linearity on the 6SN7, try a self bias resistor of 1k and a plate load of 25k Ohms. Adjust if needed from there.
Just my $0.02
Enjoy Building and Listening!
16V / 0.04A = 400 Ohms. Start with a self bias resistor of 390 Ohms, and adjust as necessary to get 40mA.
For some linearity on the 6SN7, try a self bias resistor of 1k and a plate load of 25k Ohms. Adjust if needed from there.
Just my $0.02
Enjoy Building and Listening!
Hi!
Where did you get the schematic from? That 7591 cathode resistor (40 ohms) will fry the tube, I think. Probably a typo. There are other less catastrophic problems, but I would start with that one.
PS I just saw 6A3sUMMER comment, it is all there.
Where did you get the schematic from? That 7591 cathode resistor (40 ohms) will fry the tube, I think. Probably a typo. There are other less catastrophic problems, but I would start with that one.
PS I just saw 6A3sUMMER comment, it is all there.
A couple of changes, one to decouple the input stage supply from the output one, and adding a grid stopper to the output tube.
Since you're in Sweden I'd suggest an alternative of using EL12n outputs, cheap from BTB and Reichelt. The main thing is that you have a gain (mu) of around 18. This is the setup I use for all my SE amps - high gain output tube and low gain input tube. For input I prefer the 5 pin tubes 27, 37, 56, 76. They sound great. The 6SN7 has a bit too much gain.
1. Your power amplifier might need more when using a typical phono only preamp (40dB gain = 100; 100 x 5mv rms = 0.5Vrms)
Versus . . .
The power amplifier gain you need from a typical CD player (2.1Vrms, 3.0V peak with the DAC at Full Scale).
That is about 12.5dB difference between some phono signals and some CD signals.
I admit that phono cartridges do put out more than 5mV, but output voltage versus frequency varies widely according to the Inverse RIAA curve.
All Generalizations have exceptions.
2. 6SN7? u = 17 to 20. Should you use it, or should you not use it?
After our 600 tests of the 6SN7 for the article "Parallel Tubes Effects" in Glass Audio . . .
We continued with more tests and found the 6SN7 could put out a linear signal of +/- 80V peak.
All of us have our opinions.
Versus . . .
The power amplifier gain you need from a typical CD player (2.1Vrms, 3.0V peak with the DAC at Full Scale).
That is about 12.5dB difference between some phono signals and some CD signals.
I admit that phono cartridges do put out more than 5mV, but output voltage versus frequency varies widely according to the Inverse RIAA curve.
All Generalizations have exceptions.
2. 6SN7? u = 17 to 20. Should you use it, or should you not use it?
After our 600 tests of the 6SN7 for the article "Parallel Tubes Effects" in Glass Audio . . .
We continued with more tests and found the 6SN7 could put out a linear signal of +/- 80V peak.
All of us have our opinions.
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How was the 6sn7 biased for this experiment? I find schematics with 150v 4ma to 250v 8ma. The latter should give the best linearity. According to the tube data sheet atleased. Real world might be different though? 😊
Datasheet mu for a valve is calculated at constant Ia (CCS anode load), therefore a circuit using a resistor anode load will have less mu. And that can be varied between limits by changing the anode resistor value.
The cool kids try and stick with E12 components. 390 instead of 400 ohm, 27k not 25k etc. There is no reason not to.
Big thanks to everybody 🙂
So the new schematic with all of your inputs looks like this:
The tubes are already in my possession and won't be changed at this moment. The amplifier is going to be used with both RIAA and a streamer so i might need to add a preamplifier, but we will see.
So the new schematic with all of your inputs looks like this:
The tubes are already in my possession and won't be changed at this moment. The amplifier is going to be used with both RIAA and a streamer so i might need to add a preamplifier, but we will see.
The amp has been in the works for some time, even though the schematic was not complete, and looks like this:
The nob in the front is for impedance selection, switchable betweed 4, 6 and 8 ohms. I might add a volume control as well. But i believe i might have to use a preamplifier anyways to get all the inputs I need.
Ps, sorry for all the missspelling. Can't seem to get autospelling to work and english is not my main language...
The nob in the front is for impedance selection, switchable betweed 4, 6 and 8 ohms. I might add a volume control as well. But i believe i might have to use a preamplifier anyways to get all the inputs I need.
Ps, sorry for all the missspelling. Can't seem to get autospelling to work and english is not my main language...
The load impedance on an input tube's plate that uses a CCS load is:
The CCS impedance
In Parallel with
The next stage's grid resistor, RG.
Do not forget RG, it will reduce gain to be less than mu (u), no matter how small the gain reduction may be, or may not be.
And some CCS impedances are lower at high frequencies than at midfrequencies.
The CCS impedance
In Parallel with
The next stage's grid resistor, RG.
Do not forget RG, it will reduce gain to be less than mu (u), no matter how small the gain reduction may be, or may not be.
And some CCS impedances are lower at high frequencies than at midfrequencies.
Agreed. Datasheet mu is always an ideal value. I do not even know if they measure it or just calculate it from the datasheet 's average curves. Also the fact that datasheets show values for a typical tube, while real samples will vary, hopefully not too much.
The 2200uF cap bypassing the 390 ohm resistor seems about 10x too big. I think it should be a 220uF cap. This is probably where the mistake in the first schematic came about, the last 0 came off the 400 ohm resistor and landed on the 220uF cap! Making both wrong by an order of 10!