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Old 28th May 2020, 11:34 PM   #21
Mancave62 is offline Mancave62  United States
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Join Date: Jan 2016
Location: Baton Rouge
Quote:
Originally Posted by SandorS View Post
Hi PaczeltF,

I noticed my TU-8200 has no jumpers inside that'd allow to change modes UL, triode and pentode. I asked the local shop I purchased from and got confirmed they soldered the pentode mode, for some reason. Gosh.
Think will bring back to fix it. And why the pentode, if any?

I also noticed that TU-8800 looks to allow UL or triode mode.
For my education, what does UL really do? Can it really blend the good from pentode and triode modes?
The Elekit manual just says it's meant to be an intermediate mode between the two other. And sonically, can one say UL is more close to either the pentode mode or the triode?

I enjoy writing irrelevant things in a thread it does not fit to.

Well I connected my Benz Ace MC via an all valve phono stage to the TU-8200. Wow. Welcome music.

Thanks a lot.

Sandor
I have had my Tu-8200 for several years now, I much prefer the Pentode mode and that's all I every use now. Considered soldering it in because the jumper seems so flimsy, but it works fine, so I left it adjustable. I have rolled many tubes (KT88, KT77, EL34, 6l6GC, KT66, 6550, 6ca7, 7581A). They all sound great to my ear. My favorites are the KT77, 6ca7, and what I'm stuck on now is the 7581A (6l6GC on steroids). Tube rolling is a blast, have fun!
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Old 29th May 2020, 06:46 PM   #22
SandorS is offline SandorS
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Thanks man
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Old 29th May 2020, 07:08 PM   #23
SandorS is offline SandorS
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Join Date: May 2020
Hi Paczeltf, Thanks
Will play with the modes if I can. Saw adaptors on ebay that are said to convert a tube running in pentode mode to triode mode. Or just blows up the thing.

I guess you tweaked the amp to be able to use ecc83?
Far beyond my capabilities.
But I appreciate ecc83 tubes, running in my phono.


Quote:
Originally Posted by paczeltf View Post
Hi Sandor,



The Tungsram sounds much better than the stock Chinese 12AU7 that came with my amp, but I doubt that is because better linearity. All ECC82 types of tubes share the same specifications. You need to go with a different tube family for better linearity, which is what I did.



All these modes relate to the extent of the modulation of screen grid voltage with the output signal, which creates a local negative feedback in the power tube section.

In pentode mode, the screen grid is connected to a fixed voltage with no feedback, in case of the TU-8200 it is the power supply voltage (B+). This gives the highest output power (well this is why tetrodes were invented), but also the highest output impedance and distortion in general.

In triode mode, the screen grid is connected to the anode giving 100% modulation. This will result in a triode-like characteristics with better linearity and lower output impedance, but the power drops more than 50%.

The so-called "Ultralinear mode" was invented trying to do some experiments with partial feedback rather than calculations. It turned out that about 40% modulation on the screen grid coming from an intermediate tap of the output transformer gives almost as much power as pentode mode with distortion figures being close to the triode mode. This is the preferred mode in TU-8200 as well.

There is a lot of information available on the net, search for "ultralinear mode plate characteristics".
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Old 29th May 2020, 08:04 PM   #24
paczeltf is offline paczeltf  Hungary
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TU-8200 Compatible Power Tubes
Quote:
Originally Posted by SandorS View Post
Hi Paczeltf, Thanks
Will play with the modes if I can. Saw adaptors on ebay that are said to convert a tube running in pentode mode to triode mode. Or just blows up the thing.
This type of adaptor may cause oscillations. I would skip on this.

Quote:
I guess you tweaked the amp to be able to use ecc83?
Nope. Just read through the thread that I opened.
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Old 8th June 2020, 04:47 PM   #25
SandorS is offline SandorS
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Join Date: May 2020
Thanks Paczeltf. I notice I missed a whole lot info I went through now a couple of times. I repect the knowledge and all experiment.

May I ask these for my understanding:

- What impedance range of a headphone you think fits, without the modification you suggest in your spreadsheet? Is that like 90 ohm plus, or even higher? My current headphone has 70 ohm nominal impedance. Thinking to buy a Senn HD 650 (300 ohms) at some point.
Btw have you received any inputs since, re weather the unit in TU 8200 R with adjutable headphone impedance is available separately thus can be installed for Tu 8200?
- Your mod of C22, does help to reduce hum for all headphones or just those above / outside the impedance range you determine in prior point?
- Your mods in the spreadsheet, can you think whether the different modes benefit differently from these? Or, all modifications are beneficial for the UL, triode and the pentode modes, too?
- Your mods in the spreadsheet, they are to do all or none, right (except the ones you indicate as are optional)?


Any advice or thought is appreciated.

Thanks
Sandor




Quote:
Originally Posted by paczeltf View Post
This type of adaptor may cause oscillations. I would skip on this.



Nope. Just read through the thread that I opened.
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Old 8th June 2020, 08:30 PM   #26
paczeltf is offline paczeltf  Hungary
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Join Date: Jan 2018
Location: Budapest
TU-8200 Compatible Power Tubes
Quote:
Originally Posted by SandorS View Post
- What impedance range of a headphone you think fits, without the modification you suggest in your spreadsheet? Is that like 90 ohm plus, or even higher? My current headphone has 70 ohm nominal impedance. Thinking to buy a Senn HD 650 (300 ohms) at some point.
It depends on the phones. Some tolerate high output impedance, some don't. Focal Clear, for instance, do not, which is something I expected after reading the review in a well known magazine. High impedance Sennheisers usually like being driven like that.

Quote:
Btw have you received any inputs since, re weather the unit in TU 8200 R with adjutable headphone impedance is available separately thus can be installed for Tu 8200?
Please ask Victor, but my understanding is that no upgrade kit is available.
Also note that even though the output level on the revised model is jumper-selectable, the output impedance is still high. (I explained this in another thread btw.)

Quote:
- Your mod of C22, does help to reduce hum for all headphones or just those above / outside the impedance range you determine in prior point?
Any phones.

Quote:
- Your mods in the spreadsheet, can you think whether the different modes benefit differently from these? Or, all modifications are beneficial for the UL, triode and the pentode modes, too?
The changes are irrespective of the chosen mode and all of them should benefit.

Quote:
- Your mods in the spreadsheet, they are to do all or none, right (except the ones you indicate as are optional)?
C22 is the most important one especially in case of 50Hz mains frequency. D7/R64 are also mandatory if you want to try a driver tube with higher heater current.
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