I have not done the driver portion of the mod but I did try a set of
5965A tubes and it brightened up the sound (sounds more lively).
I best put a disclaimer: I'm not really an audiophile I'm just a guy who likes
to listen to music so that's my end goal, If it sounds good to me then I like it.
5965A tubes and it brightened up the sound (sounds more lively).
I best put a disclaimer: I'm not really an audiophile I'm just a guy who likes
to listen to music so that's my end goal, If it sounds good to me then I like it.
Yes, I removed all four capacitors in the driver stages. The sound with the 5963 shows in my humble opinion more definition and therefore sounds more lively. The higher definition may be why it kills sibilance.
The B+ voltage is my first suspect as it may lead to increased distortion; is this a correct assumption? The plate voltage on the E80CC is about 135V and the B+ voltage (at point 9) is 208 V. The plate of the power tube shows 277V.
The B+ voltage is my first suspect as it may lead to increased distortion; is this a correct assumption? The plate voltage on the E80CC is about 135V and the B+ voltage (at point 9) is 208 V. The plate of the power tube shows 277V.
Did you replace the original Chinese tubes that came with the amp? If yes then practically any high quality 12AU7/ECC82 would make it sound more lively.
The 5963 is a 12AU7 variant with slightly higher gain but with the same (non-linear) characteristics.
Sorry, I do not understand this statement. Higher definition should increase sibilance, warm and lush sound can eliminate it.
Your measurements suggest that your power line voltage must be around 240V, otherwise the values are OK.
I recommended removing the cathode bypass caps from the driver stage first and check how it sounds. I do not know your source, transducers, which may well be the source of sibilance. The laid back characteristics of the original amp may balance it to some extent. The stock EH 6L6GC also has slightly coarse treble but I would not call it sibilant.
Thank you all for the response on my observations.
It is nice to know, that the high voltage is not the prime suspect.
The sound of a system depends on so many interacting factors, that a straightforward resolution is seldom found. It may well be that by me changing components, like the tubes, coupling capacitors and the driver stage for example, the complete chain leans to much to fast and bright so that my headphones (Beyer Dynamica 880) and my modified Dali Ikon speakers ( known to be bright) tend to break up in the 3 - 6khz range where sibilance is thought to originate.
Modern hifi sources also have a tendency to lean to the high frequencies.
It is nice to know, that the high voltage is not the prime suspect.
The sound of a system depends on so many interacting factors, that a straightforward resolution is seldom found. It may well be that by me changing components, like the tubes, coupling capacitors and the driver stage for example, the complete chain leans to much to fast and bright so that my headphones (Beyer Dynamica 880) and my modified Dali Ikon speakers ( known to be bright) tend to break up in the 3 - 6khz range where sibilance is thought to originate.
Modern hifi sources also have a tendency to lean to the high frequencies.
What kind of grid stoppers did you mean? There are screen grid stoppers installed for the power tubes. The value is a compromise, it is fine for Triode and UL modes, and a bit lowish for Pentode mode.
Control grid stoppers are not that important and some resistors partially serve that purpose anyway, it is not a guitar amp that you want to override constantly. It is not worth messing up the PCB for these things.
Control grid stoppers are not that important and some resistors partially serve that purpose anyway, it is not a guitar amp that you want to override constantly. It is not worth messing up the PCB for these things.
I mean the control grid stoppers.
The screen grid stoppers in the tu-8200 may be a bit low in value according to the widely reccommended value of 300 ohms for triode and 1k - or more - for UL use.
Control grid stoppers not only play a damping role in overdriven guitar amplifiers, where the control grid may be driven high in the positieve voltages, hut also have a role in suppressing parasitic oscillations in the very high frequency range and RF interference. I observe that a lot of literaturen reccommands these grid stoppers and most designs in hifi show these grid stoppers, but they are lacking in a a lot of Chinese builds and cheaper products tfrom other origens (also the screen grid stoppers are frequently lacking) .
The 12AU7 may not need them as much as, for example the ecc88, but for 6L6 and EL34 control grid stoppers are considered a must. Values of 1k and higher are usual. The high power pentodes are known to oscillate in the Mhz-range. It is frequently argued that neither input pots nor grounded grid leak resistors van serve these functions.
I like to know if there is any experience with the TU-8200 showing oscillations in high frequencies?
The screen grid stoppers in the tu-8200 may be a bit low in value according to the widely reccommended value of 300 ohms for triode and 1k - or more - for UL use.
Control grid stoppers not only play a damping role in overdriven guitar amplifiers, where the control grid may be driven high in the positieve voltages, hut also have a role in suppressing parasitic oscillations in the very high frequency range and RF interference. I observe that a lot of literaturen reccommands these grid stoppers and most designs in hifi show these grid stoppers, but they are lacking in a a lot of Chinese builds and cheaper products tfrom other origens (also the screen grid stoppers are frequently lacking) .
The 12AU7 may not need them as much as, for example the ecc88, but for 6L6 and EL34 control grid stoppers are considered a must. Values of 1k and higher are usual. The high power pentodes are known to oscillate in the Mhz-range. It is frequently argued that neither input pots nor grounded grid leak resistors van serve these functions.
I like to know if there is any experience with the TU-8200 showing oscillations in high frequencies?
I know all this, but this amp was designed and tested without control grid stoppers next to the power tubes just like all other Elekit amps that I have seen. The PCB layout and the high frequency compensation in the GNFB is at least as important and no one has yet complained about oscillations. The only measurement that I saw does not show any trace, all it tells is that the OPT iron core is a bit smallish.
I am not sure if URLs can be posted according to the forum rules. If not, I can send you in PM.
I suspect that the generic recommendation on the control grid stoppers came from the experience with average DIY builders, who use unknown cables and point-to-point wiring with an unpredictable layout, and have no tools to control the results. This all can lead to hum and parasitic oscillations.
I suspect that the generic recommendation on the control grid stoppers came from the experience with average DIY builders, who use unknown cables and point-to-point wiring with an unpredictable layout, and have no tools to control the results. This all can lead to hum and parasitic oscillations.
I think I found the source of my problems with harshness and sibilance.
The coupling capacitors I used are way too bright in a high voltage application like a tube amp. I used Obbligato premium film capacitors 220nF, which type of capacitors I liked very much in a speaker crossover where they are not harsh and show fine bass.
By changing them for Mundorf Supreme 220nF in the TU8200 I solved the problem. ( I also changed the cathode FB resistor back to 18 Ohms for the E80CC)
Experimenting with the Obbligatos in other tube amps confirmed my suspicions.
The coupling capacitors I used are way too bright in a high voltage application like a tube amp. I used Obbligato premium film capacitors 220nF, which type of capacitors I liked very much in a speaker crossover where they are not harsh and show fine bass.
By changing them for Mundorf Supreme 220nF in the TU8200 I solved the problem. ( I also changed the cathode FB resistor back to 18 Ohms for the E80CC)
Experimenting with the Obbligatos in other tube amps confirmed my suspicions.
Adding to my last post.
I had some free time and tried a few of my best power tubes with wich I have also experience in other amps.
So over some hours I tried a few 6l6GC strong UOS : Sylvania, GE and Chinese modern production.
EL34 I do not like.
The best result in my humble opinion I got with modern Genalex Gold Lion KT77. Very analytical, lots of microdetail and natural from high to low frequencies. What ever kind of music I throw at it, comes out fine: Jazz, Pop, Classical voices, orchestra or chamber music.
The extra .8 A for the heaters, in addition to the extra .6 A for the E80CC, is no problem: the power transformer stays around 57 degrees Celsius over hours. The casing gets heated up extra by the tubes.
Taste is personal, but I recommend the experiment.
Thanks again for all the feedback on this nice build.
I had some free time and tried a few of my best power tubes with wich I have also experience in other amps.
So over some hours I tried a few 6l6GC strong UOS : Sylvania, GE and Chinese modern production.
EL34 I do not like.
The best result in my humble opinion I got with modern Genalex Gold Lion KT77. Very analytical, lots of microdetail and natural from high to low frequencies. What ever kind of music I throw at it, comes out fine: Jazz, Pop, Classical voices, orchestra or chamber music.
The extra .8 A for the heaters, in addition to the extra .6 A for the E80CC, is no problem: the power transformer stays around 57 degrees Celsius over hours. The casing gets heated up extra by the tubes.
Taste is personal, but I recommend the experiment.
Thanks again for all the feedback on this nice build.
