Where's my voltage gain?!

[jimboyogi]

I understand the no-hard-sums approach Alex, my degree is in applied wine science! Looking at the static anode characteristic graph, my beginner understanding is that it has to with the available voltage for possible voltage swing, and the slope of the grid curves where they intersect the load line affecting the extent of voltage gain. The LED bias just sets a constant bias voltage, as dictated by that particular LED colour/brightness etc. This bias voltage doesn't change when you change the plate load resistance and therefore plate current, as it would using a cathode resistor. It also doesn't change as the cathode current goes up and down in response to an AC signal, which is why there is no need for a cathode bypass capacitor.

Seriously though, i couldn't hope to explain it as well as Merlin B does here - The Valve Wizard

I bought the book, much easier to flick back and forth to try and understand.

[jimboyogi]

Load resistance for EL84 Class AB two tubes in PP is Raa = 8 kOhm, not 5.3 kOhm. OT with Raa = 5.3 kOhm is probably for 6V6. EL84 and 6V6 has diferent load resistance. Perhaps it is less total amplification for it.
EL84 Data
http://www.drtube.com/datasheets/el84-philips1969.pdf

vintagekiki, the valve/tube that I was referring to is a ECF82, a medium mu triode and a sharp cutoff pentode in the same bottle. This is a small signal (or preamp) valve. I am wondering if you are confusing this ECF82 with the EL84 ouput pentode?

[vintagekiki]

I am all the time talking about the output stage your amplifier, about load resistance for PP output stage with pair EL84. Load resistance that you mention Raa = 5.3 kOhm is not suitable for PP EL84, and output tubes simply are not adequately adjusted. PP output stage with pair EL84 should have a load resistance of about Raa = 8kOhm.
I know very well what is ECF82. I have 62, telecomunication engineer by profession. and I grew up with the tubes. To be able to conduct any constructive exchange of opinions, it is necessary schematics for your amplifier. Discussion without schematics is story in the wind. I do not see what so much secrecy about your schematics. When study the whole schematics of your amplifier, then we can talk professionally about voltage gain, about ECF82, about any thing.
You may not understand me, because of my poor knowledge of languages, sorry I use a translator in both directions.

[Merlinb]

I am all the time talking about the output stage your amplifier, about load resistance for PP output stage with pair EL84. Load resistance that you mention Raa = 5.3 kOhm is not suitable for PP EL84,

Calm down! Jimboyogi did not mention the EL84 in his first message. He is only interested in the ECF82 preamp, which he says has an internal anode resistance of 5.3kOhm (mu/gm). He is not talking about a load resistance.

[Alex/Tubewonder]

Ah, but our "transconducting" friend will not even consider a possibility of ever being wrong.

[vintagekiki]

Disagreement is in the wrong identification of parameters.
Jimboyogi wrote ra ~ = 5.3K ohms. ra ~ is a sign for load resistance not for internal tube resistance. Internal tube resistance have a sign Ri or Rp without ~

useful link
http://livinginthepast-audioweb.co.u...egaincalcs.php (Calculating The Voltage Gain For A Valve)

[jimboyogi]

Disagreement is in the wrong identification of parameters.
Jimboyogi wrote ra ~ = 5.3K ohms. ra ~ is a sign for load resistance not for internal tube resistance. Internal tube resistance have a sign Ri or Rp without ~

useful link
Calculating Valve Voltage Gain (Calculating The Voltage Gain For A Valve)

vintagekiki, sorry about the misunderstanding!
I was using ~ as meaning 'approximately', I never knew that it had some EE meaning. Also I have been getting my theory largely from merlin b's book, where internal tube resistance is denoted as 'ra' and external anode load resistance as 'Ra'.

Also, thanks for the link, very interesting reading, and mentions the ECF82. There it states " The triode, however, is useless as a voltage amplifier and is best kept to cathode follower and phase splitter functions." I thought that mine was sounding pretty good!

Thanks for your assistance

[Merlinb]

Disagreement is in the wrong identification of parameters.
Internal tube resistance have a sign Ri or Rp without ~

This is incorrect in English-speaking countries (it may be different in other languages). The internal tube resistance is a dynamic or AC resistance, and these are always given a small letter 'r'. The anode load resistor is a static or DC resistance and is given a big letter 'R'.

In England:
ra = internal anode resistance.
Ra = anode load resistor.

In USA:
rp = internal tube resistance.
Rp = plate load resistor.

Hope this helps avoid confusion!

[vintagekiki]

@ Jimboyogi. Again sorry. because my language is poor. Therefore, knowledge of the profession is not.
Pre amp tubes with higher anode current has less voltage amplification. Voltage amplification is required in pre amp stage. Tube with greater anode current, had higher current amplification and used in the drivers or exciters stages. ECF80 (82) was well seen tubes in phase splitter (inverter)

Personally, I think for biasing pre amp tubes is not practical to use LEDs. Current through the LEDs depends on the pieces to pieces. For tube biasing required precise correct values of current. To do this, use the current regulator diodes.
http://eu.mouser.com/Semiconductors/...des/_/N-2xpt0/

Boogie in MK II for biasing pre amp tubes used also current regulator diode TCR5304
http://www.americanmicrosemi.com/inf...?ss_pn=TCR5304

@ Merlinb. To clarify some terms, to better understand.
ra ~ = 5.3K ohms means the anode load resistance or impedance.
ra ~ 5.3K ohms means approximately
RA = 5.3K ohms means the internal tube resistance
If there is an equal sign ( = ) beside him can not stand approx sign ( ~ )

Large or small letter r certainly have meaning. But who understands, understands, independently from the size letters. For ECF82 from the data sheet shows the fact that the internal tube resistance aprox 5 kOhm. In the case as written here a sign ~ behind the ra, refers to the load impedance tube, rather than internal tube resistance.

[Wombaticus]

Any English speaker would automatically read "~=" as "approximately equal to". This is seen more frequently, I think, than just "~" in this usage.

[vintagekiki]

@ Wombaticus Using the logic of something that was approx, can not be approx equal. Approx means that there around some values, but equal that means exactly is this value. As I said my knowledge of languages is poor, leaving the grammar, this is a technical topic, and back to Where's my voltage gain.

[Wombaticus]

@ Wombaticus Using the logic of something that was approx, can not be approx equal. Approx means that there around some values, but equal that means exactly is this value. As I said my knowledge of languages is poor, leaving the grammar, this is a technical topic, and back to Where's my voltage gain.

This was not about logic, it was about how language is used everyday, in order that you might make yourself better understood. But to be clear, your logic is flawed: the single tilde alone is used to indicate a poor approximation, sometimes only within an order of magnitude. A double tilde is used to indicate the notion that something is approximately equal to some other value. And, of course, there can be a notion than something is a near approximate, rather than just a rough approximate. However, since the double tilde (≈) is not a standard keyboard character, this is usually rendered as "~=" online.

[vintagekiki]

@ Wombaticus I looked how official tube manufacturers denote the tube parameters.
http://www.drtube.com/datasheets/el84-philips1969.pdf
Please look at page 3
Internal resistance is marked Ri
Load resistance is marked Ra ~

Precisely are defined and written values the working conditions of the tube. They are not defined as approximate. Approx labeling is rather indefinite. Can be interpreted from case to case or can but not necessarily.
Many buildings failed because approx voltage, approx resistor, approx capacitor, approx … … Everything is approx, but the amp will not work properly.

If we want to be just as accurate again, let's look at a precise definition of approx.
http://en.wikipedia.org/wiki/Table_o...atical_symbols
x ≈ y means x is approximately equal to y; or π ≈ 3.14159

I am not disputing your knowledge of language, logical because it is your native language, but I do not really see that you much need to practice linguistic precision when I said that my knowledge language is poor. With all due respect you, I will follow the professional part of the topic

[Wombaticus]

Dude, whatever. I was just trying to help you be more readily understood, by, well, everyone else here.

[Merlinb]

Please look at page 3
Internal resistance is marked Ri
Load resistance is marked Ra ~

That is a Philips data sheet (Danish). Alternatively, see page 1 of the Mullard English data sheet:
http://www.mif.pg.gda.pl/homepages/f...129/e/EL84.pdf
Internal resistance is marked ra.

In any case, data sheets are not academic sources; they often contain notation errors. (For example it is common to see "KHz", rather than the correct "kHz").

Precisely are defined and written values the working conditions of the tube. They are not defined as approximate.

But it is correct to say that the internal tube resistance is "approximately equal to..." when the operating point is undefined or unknown, as it often is when designing a circuit from the start.