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Old 14th August 2012, 03:44 AM   #1
opa1 is offline opa1  United States
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Default EL84 in UL

I have a quick question about running a EL84 se in UL. The opt's are gxse15 5k with 40% taps. What will change? Its a rh84 design in triode.
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Old 14th August 2012, 04:26 AM   #2
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I have a quick question about running a EL84 se in UL. The opt's are gxse15 5k with 40% taps. What will change? Its a rh84 design in triode.
If you are in ultralinear, there is no triode.
The screen grids will connect to the 40% taps.

Last edited by soundguruman; 14th August 2012 at 04:31 AM.
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Old 14th August 2012, 04:32 AM   #3
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I know, I was asking what difference if any by changing to UL.
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Old 14th August 2012, 04:40 AM   #4
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I know, I was asking what difference if any by changing to UL.
It can have more output power, and low distortion at lower power levels.
But when the power level gets up near maximum, it has more distortion than a triode amplifier. Won't sound quite as sweet.
That's a good way to describe it.

So if you don't crank it up all the way, it dissipates more power on peaks, with reasonably low distortion at normal lower levels.. Tubes last longer...It's a compromise between heat and distortion.
The distortion is still nice compressed kind of distortion, it still sounds good.

But if you are cranking it way up all the time you are better off class AB, as far as buying tubes a lot.

Last edited by soundguruman; 14th August 2012 at 05:02 AM.
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Old 14th August 2012, 04:56 AM   #5
opa1 is offline opa1  United States
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No, not going pp. Low volume is all i do. Just wondering about sound quality.
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Old 14th August 2012, 05:04 AM   #6
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No, not going pp. Low volume is all i do. Just wondering about sound quality.
At low volume it still has nice low distortion,
but it saves the tube life compared to triode.

When the screen grid is energized, it makes the plate less sensitive.
So, it may need a bit more signal from the preamp, but not a bunch more.

It comes down to how nice of a transformer is possible.
The transformer will make or break the sound quality.

Last edited by soundguruman; 14th August 2012 at 05:30 AM.
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Old 14th August 2012, 05:13 AM   #7
ChrisA is offline ChrisA  United States
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Originally Posted by opa1 View Post
I have a quick question about running a EL84 se in UL. The opt's are gxse15 5k with 40% taps. What will change? Its a rh84 design in triode.
Here is the way to think about UL...

In triode mode the screen's voltage goes up and down with the audio signal because it is connected to the plate. You don't get much power from the tube in this mode but in triode mode you get mostly 2nd harmonics and many people like the sound of second harmonics

In Pentode mode the screen remains at a constant high voltage. The tube can produce the most power in this mode.

In UL mode you are roughly half way between the two above modes.

It is not hard to install a 3-way switch to switch modes. Just do NOT operate the switch with the power on. Hide it inside the chassis
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Old 14th August 2012, 05:32 AM   #8
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Half way between is a good way to explain it.
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Old 14th August 2012, 03:00 PM   #9
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Originally Posted by opa1 View Post
I know, I was asking what difference if any by changing to UL.
UL is simply one form of local negative feedback.

The gain of UL-connected output stage is higher than in triode mode, but a little lower than in pentode. This has effect to the sensitivity of the amplifier.

The output impedance in UL-mode is much lower than in pentode, but slightly higer than in triode. UL and triode can sometimes be used without GNFB but pentode never in Hifi purpose.

Maximum output power in UL is essentially higer than in triode mode and a little smaller than in pentode.

The minimum distortion depends on bias, load and individual tube in all modes, not so much on operating mode.
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Old 14th August 2012, 03:11 PM   #10
opa1 is offline opa1  United States
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Thanks for the interpretations of ul. Making it switchable sounds like a good idea.
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