Sure.
Attached is the schematic of my VHex+ amplifier.
Q5 is the CCS.
Iccs = (V(LED) - Vbe) / R15 = (1.8 - 0.65) / R15 = 1.15 / R15
Attachments
Did the change but this time the bias is not increasing with various resistance values for bias increment.
Hard to tell right away - I didn't study Hitachi circuit in detail.
I'm sure it will work if the right operating points are arranged.
There may be a countless number of ways to prevent those transistors from closing at idle.
12AU7 has got the same heater power consumption = 2 x 0.3A = 0.6A (6.3V).
6SN7 is not good for this circuit, as it will have positive bias (grid is more positive than cathode), resulting in grid current - not good at all.
Be careful arbitrarily substituting one tube for another. In general, this will not work well unless the circuit component values are changed to allow the new tube to bias correctly. Until you have a working circuit, I'd stick with the 12AU7 that the circuit was designed for.
+35V DC at the anodes. Not many tubes work well at this kind of low voltage.
12AU7 (ECC82) does work well. 6DJ8 is the other one that works well, but in this circuit it requires much more degeneration due to its significantly higher trans-conductance.
So, as Ray just mentioned - it's not possible to just substitute the tube.
You are talking about a completely different amplifier than the one Valery designed in this thread. First, the 12AU7 for which the amp was designed is a 9-pin Noval tube; the 6SN7 has an octal base. Substituting an octal tube for the Noval would require that the circuit board be redesigned. Second, raising the tube B+ to a level that would be appropriate for the 6SN7 would require an additional high voltage power supply, again changing the design considerably.
Why don't you just build the amp the way that Valery designed it and see how it sounds?
What are your concerns? Please let us know, otherwise we don't understand why you want to change 12AU7 to something else.
What do you mean "the smallest"? In size? For what reason do you care about the size? 12AU7 is smaller than 181CT-Z.
Changing one tube with the other will change the amplifier's "signature". It will lead to so many other changes, that it will result in a completely different amplifier. It will most likely not make it any better - it's already very good. It will just make it different.
I'm trying to understand, what exactly you'd like to achieve. What the requirements are.
I want to use one of the finest tubes available.
Would like to choose the one from here.
Shuguang Treasure Vacuum Tubes – Select – NEW! | Psvane & Shuguang Treasure Audio Tubes
The question is - finest for what?
Again - example from the automotive industry.
I'm offering you a Mercedes. You're saying - why don't we put a Ferrari engine into it? Ferrari engines are the best ones available (for what? but that's a different topic).
I'm saying - ok, everything is possible, but we need to completely re-design the car for that. It will be completely different from the finest, balanced in all the aspects, well-tested, reliable design we already have. Ferrari engine has got more power and more RPM, but will such a substitution result in a better car? Most likely it will not. As we still don't understand - better for what? Drag-racing? Track competitions? Interstate long-distance cruising? Supermarket shopping? Eye catching? I'm not joking )) Completely different purposes ))
TubSuMo is carefully designed for the finest sound. 181CT-Z will make it more expensive and probably more beautiful. But not better-sounding.
Sound very much depends on the tube in simple common-cathode cascades with low-loop-gain local feedback. TubSuMo utilizes the tube the different purpose. It does not sound like traditional tube amplifier due to its incomparably lower distortion.
Again - example from the automotive industry.
I'm offering you a Mercedes. You're saying - why don't we put a Ferrari engine into it? Ferrari engines are the best ones available (for what? but that's a different topic).
I'm saying - ok, everything is possible, but we need to completely re-design the car for that. It will be completely different from the finest, balanced in all the aspects, well-tested, reliable design we already have. Ferrari engine has got more power and more RPM, but will such a substitution result in a better car? Most likely it will not. As we still don't understand - better for what? Drag-racing? Track competitions? Interstate long-distance cruising? Supermarket shopping? Eye catching? I'm not joking )) Completely different purposes ))
TubSuMo is carefully designed for the finest sound. 181CT-Z will make it more expensive and probably more beautiful. But not better-sounding.
Sound very much depends on the tube in simple common-cathode cascades with low-loop-gain local feedback. TubSuMo utilizes the tube the different purpose. It does not sound like traditional tube amplifier due to its incomparably lower distortion.
TubeHex+
Just for fun. Attached are 2 schematics I designed some time ago.
1-st one has got 6SN7 at the input.
2-nd one has got 6DG8.
I personally prefer the variant with 6DG8 (from designer's point of view). This one is tested by Terry - see the square wave response pictures. 6SN7 version has never been live tested.
This is the part of a separate project - "Sons of VHex".
Rhythmsandy, if you've got enough energy, you can build both of them and see if there is some difference in their sonic signature. Not that difficult - project time frame depends on the builder's skills level. One evening exercise for Terry
Just for fun. Attached are 2 schematics I designed some time ago.
1-st one has got 6SN7 at the input.
2-nd one has got 6DG8.
I personally prefer the variant with 6DG8 (from designer's point of view). This one is tested by Terry - see the square wave response pictures. 6SN7 version has never been live tested.
This is the part of a separate project - "Sons of VHex".
Rhythmsandy, if you've got enough energy, you can build both of them and see if there is some difference in their sonic signature. Not that difficult - project time frame depends on the builder's skills level. One evening exercise for Terry
