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Old 17th January 2011, 03:24 PM   #31
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Hi,
Two things:

1.
How should I read the Power Output Simulation table Tubes & Transformers

Here is what I understand (right or wrong)

Tube: given, the tube type
B+ voltage: Given from the power transformer
Load Z: Given by the output transformer
Vp: ???
Vk: ???
Rk: Cathode resistance, a potential degree of freedom, can be change.
Ik: ???
Diss (idle): ??? What is the color code? Values should be high, low, or else?
Pwr Out: Power output, maximum energy that the amp can send to the speakers
Dist *nd: distortion, should be minimize.
DF: damping factor, show be as low as possible.

Can you shed some light on my question marks.

2.

Also, 810r is not there for the el34, but somebody suggested to use it as Rk. Why, and what will hapend?

Thanks,
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Old 17th January 2011, 07:08 PM   #32
rknize is offline rknize  United States
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B+ voltage: Measure this voltage on the red wire of the output transformer.
Vp: Plate voltage, measured at the blue wire of the output transformer
Vk: Voltage across the cathode resistor
Ik: Current through the cathode resistor

Diss (idle): Tube plate dissipation with no audio input. Orange values are nearing the maximum dissipation of the tube type and red is nearing the danger zone. However, this value depends on the manufacturer too. Some 6L6 types can handle quite a bit more than the max without plate glow (my JJs do) while others start to glow ever before reaching these values. The part George specs is conservative, though some people have had to go with higher value cathode resistors. The Chinese 6L6 types seem to have this problem. Other types vary as well.

Dist *nd: Try to minimize to some extent. You can see how larger Diss values tend to yield lower distortion numbers. In short, you are trading tube life for better distortion characteristics.

DF: This may or may not be important. It depends on how difficult your speakers are to drive.
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Old 20th January 2011, 01:05 AM   #33
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Hi,
I just measure my B+ and it is 475V. I don't want to keep swapping the Rk, but would like to be able to swap between el34 and kt88.

1. What would be the optimal Rk to be able to do so?

If I prefer one type of tube more than the other:

2. Which values of Rk should I have in my toolbox if I want to run optimally the el34?

3. Which values of Rk should I have in my toolbox if I want to run optimally the kt88?

B+ = 475V is not in the simulation table Tubes & Transformers (bottom)

Thanks
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Old 20th January 2011, 01:40 AM   #34
rknize is offline rknize  United States
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1) I wouldn't go lower than 560 ohm for your EL34s at 475 of B+. That is getting pretty close to the theoretical maximum. To get your actual plate dissipation with your current setup, you can measure the voltage (Vk) across the cathode resistor to get Ik and use the plate voltage to calculate Diss (this assumes triode mode):

Ik = Vk / Rk

Diss = (Vp - Vk) * Ik

2) Since you don't want to run the EL34 much hotter than it is in #1 (assuming your calculations agree), the answer is the same.

3) Some KT88 types can handle more current than others. New Sensor tubes (EH, Tung-Sol reissue, etc) can handle more than the SED KT88, for example. If I were to take a stab at it using the chart, 430 or 390 ohms would get you near the sweet spot.

As far as 475 not being in the chart...you need to look at the 450 and 500 numbers and extrapolate.
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