The 2nd harmonic suppression is present over the whole frequency range. 'Normal'/expected behavior at 1 Watt output power; the 2nd harmonic dominates THD:
At 1.5 Watt, the 2nd is suppressed:
And here is the output level (voltage) as function of frequency; the resonant behavior is pretty obvious:
At 1.5 Watt, the 2nd is suppressed:
And here is the output level (voltage) as function of frequency; the resonant behavior is pretty obvious:
At 1.5W, the output transformer shouldn't be stressed in any way, should it? I can't find the data sheet for the 2777B, but it's supposedly similar to the 2783C (OPT for the TU-8800), which is supposedly similar to the 2785C (OPT for the TU-8900), and that has a data sheet up at https://www.lundahltransformers.com/wp-content/uploads/datasheets/2785C.pdf .
The PTC1/PTC2 thermistors before the mode selector have a value of 120 Ohm. Changing this value can affect the effect that I find in about half of my 807 tubes, i.e. that they are "noisy like a ground loop" in Triode mode (typically, but not exclusively, Eastern European ones make noise in triode and work perfectly in the other two modes). I mean that increasing this "resistance" if I jumper to Triode mode, does the resistance between G2 and the Anode change, does the operation change?
Second question or note: on the Hificollective website, in the upgrade options under TU-8200R Kit, number "2" contains the following note: "These are specifically voiced components that target the key signal components." In this block there are two groups of resistors R7, R8, R13 and R14 27K Ohms, as well as resistor pairs R5-6 11-12 1K Ohms. The latter are, if I understand correctly, the resistors following the cathode of the drive stage. While the 27K Ohm, at least the 13-14 is the power tube, in this case it is connected to the control grid of the 807s. I'm trying to find out based on the schematic why the 8 resistors are the most affected sound according to the HFC.
This "list" by HFC is significantly narrower than what Victor gave in Ferenc's thread, as far as I remember, like the resistors that are included in the signal path.
Tailored to the "R" version, it probably looks like this:
This "list" by HFC is significantly narrower than what Victor gave in Ferenc's thread, as far as I remember, like the resistors that are included in the signal path.
Tailored to the "R" version, it probably looks like this:
| 1/2W 12 Ω 6PCS (R3, R4 , R19, R20, R21, R22) |
| 1/2W 220 Ω 2PCS (R33, R34 headphone) |
| 1/2W 1K Ω 6PCS (R5, R6, R11, R12) |
| 1/2W 22K Ω 2PCS (R29, R30) |
| 1/2W 100K Ω 4PCS (R1, R2, R15, R16) |
| 1/2W 330K Ω 2PCS (R9, R10) |
| 1W 27K Ω 4PCS (R7, R8, R13, R14) |
Gotan, are you saying there is significant current flowing through G2 and the positive temperature coefficient protection resistors, so that changing the 120 Ohm resistor value changes the sound?
Regarding your second question/note, the 27K resistors and the 1K resistors are the anode resp. cathode resistors for the 12AU7 driver tubes, so they set the working point for those tubes, and should definitely affect the amplifier performance.
I must admit it is a while that I looked at Ferencz's modification recommendations, but I thought those were mostly for (bigger) capacitors. Are these HFC recommendations changes in value, or just for more 'audiophile' components, like carbon resistors? If the latter, I think I'm a bit biased, because the last (and only) time I used carbon resistors on purpose (I.e. not because nothing else was available) was as temperature sensors. We'd wire them up, dunk them in liquid nitrogen a few times, keep the ones that would stabilize in resistance value and throw away those that kept drifting, and they made superb temperature sensors at low temperatures. Great if that's what you want, but not something to use if you want constant resistance.
Did anybody make a Spice model for the TU-8200 or TU-8200R?
Regarding your second question/note, the 27K resistors and the 1K resistors are the anode resp. cathode resistors for the 12AU7 driver tubes, so they set the working point for those tubes, and should definitely affect the amplifier performance.
I must admit it is a while that I looked at Ferencz's modification recommendations, but I thought those were mostly for (bigger) capacitors. Are these HFC recommendations changes in value, or just for more 'audiophile' components, like carbon resistors? If the latter, I think I'm a bit biased, because the last (and only) time I used carbon resistors on purpose (I.e. not because nothing else was available) was as temperature sensors. We'd wire them up, dunk them in liquid nitrogen a few times, keep the ones that would stabilize in resistance value and throw away those that kept drifting, and they made superb temperature sensors at low temperatures. Great if that's what you want, but not something to use if you want constant resistance.
Did anybody make a Spice model for the TU-8200 or TU-8200R?
Hello Gruesome, it became clear to me immediately from your answer that I messed up the punctuation mark at the end of the sentence in the original post, because I didn't want to make a statement, but to ask about the effect of the PTC's 120Ohm. 
The reason why I ask whether the resistance value of this PTC can have an effect is that I have already talked to several old experts about the anomaly with my 807 tubes.
This is how it emerged that the internal resistance of the tubes (or something else) the voltages that may appear in the wrong place, can be the cause of the buzzing sound that appears in some "weaker manufactured" tubes when I switch to Triode mode. After all, in this case, the anode and grid2 are connected using the jumper?
The "weaker manufactured" tube is also a strange approach, because it's pretty much true:
all my Sylvania 5933 tubes are flawless in Triode as well.
2 out of 3 pairs of my ATS25 tubes run great in Triode.
A pair of Hytron 807s are flawless in Triode too.
However, out of 8 Tungsram 807s, only 2 run in Triode well. Philips QE06/50s, Westinghouse, RCA 807 were also noisy, buzzing in Triode. None of the Russian G-807s run in Triode.
All tubes are flawless in all other modes (UL, Pentode).
Regarding the resistors: Hificollective only changed the "quality" of the resistors in the recommendation, they did not affect the values.
Specifically, this was their recommendation:
(AMRG2.0-500) 27K 2W Amtrans AMRG Resistor x 2 (R7,8)
(RES-3600) - 27K 1W Audio Note Tantalum Resistor x 2 (R13,14)
(PRP-1/2-330) - 1K 0.5W PR9372 Metal Film Resistor x 4 (R5,6,11,12)
There are only 2 Amtrans carbon resistors. This is obviously just a guideline, there are a lot of alternatives when it comes to resistors, and the "factory" one sounds great too, I'm just wondering if anyone has played with these resistor replacements (especially the 8 places suggested by HFC).
What does it mean the "spice model"?
The reason why I ask whether the resistance value of this PTC can have an effect is that I have already talked to several old experts about the anomaly with my 807 tubes.
This is how it emerged that the internal resistance of the tubes (or something else) the voltages that may appear in the wrong place, can be the cause of the buzzing sound that appears in some "weaker manufactured" tubes when I switch to Triode mode. After all, in this case, the anode and grid2 are connected using the jumper?
The "weaker manufactured" tube is also a strange approach, because it's pretty much true:
all my Sylvania 5933 tubes are flawless in Triode as well.
2 out of 3 pairs of my ATS25 tubes run great in Triode.
A pair of Hytron 807s are flawless in Triode too.
However, out of 8 Tungsram 807s, only 2 run in Triode well. Philips QE06/50s, Westinghouse, RCA 807 were also noisy, buzzing in Triode. None of the Russian G-807s run in Triode.
All tubes are flawless in all other modes (UL, Pentode).
Regarding the resistors: Hificollective only changed the "quality" of the resistors in the recommendation, they did not affect the values.
Specifically, this was their recommendation:
(AMRG2.0-500) 27K 2W Amtrans AMRG Resistor x 2 (R7,8)
(RES-3600) - 27K 1W Audio Note Tantalum Resistor x 2 (R13,14)
(PRP-1/2-330) - 1K 0.5W PR9372 Metal Film Resistor x 4 (R5,6,11,12)
There are only 2 Amtrans carbon resistors. This is obviously just a guideline, there are a lot of alternatives when it comes to resistors, and the "factory" one sounds great too, I'm just wondering if anyone has played with these resistor replacements (especially the 8 places suggested by HFC).
What does it mean the "spice model"?
Spice (SPICE) is an electronics simulation program, originally written by somebody at UC Berkeley, I believe. See https://en.wikipedia.org/wiki/SPICE
I'm looking at the free LTspice implementation: https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
I noticed that there is a thread on diyaudio dealing with SPICE tube models. I haven't quite figured out yet how to integrate the tube descriptions given there into a spice tube model (the text files in that thread do not seem to be complete component descriptions for spice, but rather a part of a description), and of course entering the TU-8200R schematic into Spice is quite a bit of work. That's why I asked about an existing implementation. Besides being needed to run a simulation, having a schematic drawn in LTspice would also mean we would have a schematic drawing unencumbered by the copyright issues that Victor mentioned. I think having a schematic would help the discussion. Of course there could be new copyright issues, in principle everything that anybody creates is automatically copyrighted by the creator.
Regarding buzzing in triode mode: I am not a tube expert, but my understanding is that in Triode mode the G2 grid current is added to the anode current, and, all else being equal, the usable gain and output power should be lower than in Pentode or Ultralinear mode. Buzzing sounds like distortion, so maybe you are running your tubes too 'hot' in triode mode.
I'm looking at the free LTspice implementation: https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
I noticed that there is a thread on diyaudio dealing with SPICE tube models. I haven't quite figured out yet how to integrate the tube descriptions given there into a spice tube model (the text files in that thread do not seem to be complete component descriptions for spice, but rather a part of a description), and of course entering the TU-8200R schematic into Spice is quite a bit of work. That's why I asked about an existing implementation. Besides being needed to run a simulation, having a schematic drawn in LTspice would also mean we would have a schematic drawing unencumbered by the copyright issues that Victor mentioned. I think having a schematic would help the discussion. Of course there could be new copyright issues, in principle everything that anybody creates is automatically copyrighted by the creator.
Regarding buzzing in triode mode: I am not a tube expert, but my understanding is that in Triode mode the G2 grid current is added to the anode current, and, all else being equal, the usable gain and output power should be lower than in Pentode or Ultralinear mode. Buzzing sounds like distortion, so maybe you are running your tubes too 'hot' in triode mode.
Regarding replacing resistors of the same value with "boutique" resistors: there is obviously no sound reason, since it still sounds lavish. (I admit that I don't hear too much of a difference between my different coupling capacitors).
However, regarding the cumulative G2 and anode current: if I wanted to run it permanently in a Triode and of course to test whether this is really a solution, then which resistors should I change the value of to make this cumulative current smaller?
However, regarding the cumulative G2 and anode current: if I wanted to run it permanently in a Triode and of course to test whether this is really a solution, then which resistors should I change the value of to make this cumulative current smaller?
Gotan, I don't see how you would decrease the total output current without also decreasing output power. And I do not know enough about vacuum tubes to be able to judge what modifying the value of the G2 resistor does to the overall behavior. Making it larger would obviously limit the G2 current more, but I'm guessing you would have to increase its value a lot, to achieve significant G2 voltage reduction relative to the anode, assuming that the G2 current is in the few mA range (see for example https://frank.pocnet.net/sheets/127/6/6L6GC.pdf).
I looked up the 807 tube and I am a bit confused on how you hook it up to the TU-8200(R), since this tube has the anode connection at the top. Are you using a socket adapter that brings out an extra wire for the anode?
In any case, Wikipedia claims the 807 has a maximum G2 screen voltage of 300 V, compared to the 450 V for the 6L6GC. Maybe that is the reason why the 807 behaves worse for you, bringing it close to its G2 limit in the TU-8200(R)?
I looked up the 807 tube and I am a bit confused on how you hook it up to the TU-8200(R), since this tube has the anode connection at the top. Are you using a socket adapter that brings out an extra wire for the anode?
In any case, Wikipedia claims the 807 has a maximum G2 screen voltage of 300 V, compared to the 450 V for the 6L6GC. Maybe that is the reason why the 807 behaves worse for you, bringing it close to its G2 limit in the TU-8200(R)?
Yes I am using the mentioned socket adapter with top anode cap.
G2 screen voltage could be a good way. My measured values on position 19-20 are ~270V so on the higher side of limits in user manual and a bit close to the limit of the 807's g2.
As I see in schematic no one resistor is in direct contact with grid 2.
G2 screen voltage could be a good way. My measured values on position 19-20 are ~270V so on the higher side of limits in user manual and a bit close to the limit of the 807's g2.
As I see in schematic no one resistor is in direct contact with grid 2.
They keep the values from the manual and try to sell you magic components. My proposal is the opposite one: Normal, but still high quality components with different values.
Thank you for your opinion Ferenc! So far, I have managed to resist the temptation of boutique resistors (I prefer to collect what I need from Farnell and Mouser or my desk).
Regarding the grid 2, do you have an idea how I could reduce (as a test) the voltage applied to them?
"My proposal is the opposite one: Normal, but still high quality components with different values." If you had time please tell me more about this, thank you in advance.
Regarding the grid 2, do you have an idea how I could reduce (as a test) the voltage applied to them?
"My proposal is the opposite one: Normal, but still high quality components with different values." If you had time please tell me more about this, thank you in advance.
