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Old 13th September 2019, 08:25 AM   #41
paczeltf is offline paczeltf  Hungary
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Did you remove all the four bypass caps?
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Old 13th September 2019, 04:39 PM   #42
HarryY is offline HarryY  United States
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Some thoughts on Elekit TU-8200DX
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.
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Old 15th September 2019, 10:14 PM   #43
Disque is offline Disque  Netherlands
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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.
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Old 18th September 2019, 10:17 PM   #44
paczeltf is offline paczeltf  Hungary
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Quote:
Originally Posted by HarryY View Post
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).
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.
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Old 18th September 2019, 10:31 PM   #45
paczeltf is offline paczeltf  Hungary
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Quote:
Originally Posted by Disque View Post
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 5963 is a 12AU7 variant with slightly higher gain but with the same (non-linear) characteristics.

Quote:
The higher definition may be why it kills sibilance.
Sorry, I do not understand this statement. Higher definition should increase sibilance, warm and lush sound can eliminate it.

Quote:
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.
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.
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Old 19th September 2019, 02:42 AM   #46
HarryY is offline HarryY  United States
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Some thoughts on Elekit TU-8200DX
Quote:
Originally Posted by paczeltf View Post
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.
Yes I have a few sets of 12AU7 and even tried a set of 12BH7
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Old 22nd September 2019, 09:14 AM   #47
Disque is offline Disque  Netherlands
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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.
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Old 25th September 2019, 05:37 PM   #48
Disque is offline Disque  Netherlands
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By the way: did anyone considder placing gridstoppers?
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Old 26th September 2019, 11:57 AM   #49
paczeltf is offline paczeltf  Hungary
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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.
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Old 28th September 2019, 11:21 PM   #50
Disque is offline Disque  Netherlands
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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?
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