EF40 triode connected plate resistance?

I cant find this number on the datasheets,and wonder how to go about calculating them

Pls. look at the Mazda datasheet for EF86 / 6F22 (equivalent):

Ra = 16000 Ω
gm = 2,0 mmhos
µ = 33

for Ip+g2 = 4 mA
and Va+g2 = 250 V

Regards Andreas

i didnt know they are direct equivalent of EF86....im sure they are close enough though..THANKS!

http://www.mif.pg.gda.pl/homepages/frank/sheets/030/e/EF40.pdf

page 3

moamps said:

http://www.mif.pg.gda.pl/homepages/frank/sheets/030/e/EF40.pdf

page 3

Click to expand...

An interesting data sheet because it is one of the very few that gives a low frequency equivalent noise resistance, in this case 40K. The EF86 quotes its low frequency input noise as 2uV in a 10KHz bandwidth which is close to an equivalent noise resistance of 25K - so it is a little quieter.

Cheers

Ian

> how to go about calculating them

For what plate current?? Makes a difference.

Andreas gave a value for 4mA. I'm suspecting you are thinking of a mike head amp which may run closer to 0.5mA. Assume Gm and Rp vary *roughly* as square-root of current. So at 1/10th the current, Rp may be closer to 160K.

Why do you care? Are you trying to "match" a load resistor or transformer?

> http://www.mif.pg.gda.pl/homepages/frank/sheets/030/e/EF40.pdf page 3

That's the resistance-coupled amplifier suggestions. Does not directly answer his question. In theory Rp may be inferred from this data, if there's a voltage/current condition similar to the point you intend to use it.

tubes are just variable resistors, so use ohms law.

200 volts/ 1 ma = 200, we are in ma for denominator so add K> 200K.

200 volts / 0.5 ma = 400






















K. 

I'm suspecting you are thinking of a mike head amp which may run closer to 0.5mA

Click to expand...

Exactly.
im trying to match a transformer - or to check what will be the low end roll off with my miserable (7:1)10H tx....
(i also have a 4.2:1 with 50H primary now...)

so i took the curves for triode(EF86) and tried some math based on the following quote:

Then I calculated the plate resistance (Rp). Rp is defined as a change in plate voltage divided by a change in plate current with the grid voltage held constant, so I changed the plate voltage by +10 volts and followed the grid voltage curve for a reading of plate current, which showed a change of .125mA.  So 10V/.125mA = 80000, or 80K.  (Don't forget to move the decimal!  .125mA = .000125A)

Click to expand...

so i see a .0004A change from 40V to 50V on the -1 grid line

results are written on the curves attached, but i got ~25K and 20K paralleled with the 130K resistor (100K+30K)

so,operating point is 42V @ 0.6mA ,105V B+

it seems im way off here?why?

mich said:

im trying to match a transformer -

Click to expand...

Hello,

an example of a preamplifier based an the EF40 is the Klangfilm KLV 002

http://www.audioantik.de/Kino/V002.pdf

Regards Andreas

You have Triode curves??

Dynamic plate resistance is just the *slope* of the tangent to the plate curve at the operating point.

Your curves-snippet is unclear. Is my pink line 58V 1.8mA? If so, that's 32K.

32K||130K== 26K source.

> 10H tx....

Well, 10H at 20Hz tims 2pi is 1256 ohms. You are a long way out. About 414Hz.

> 50H primary now...

5 times better. 83Hz.

PRR,
your pink line is 58V 1.8mA
but i didnt get why did you stop the line at 1.8mA .or better , what determines the angle of the slope?

Thanks !

> why did you stop the line at 1.8mA

Traditionally: the length of the match-book used to fit a straight line to the curve in the book. Matchbook gives a long-enough line that you can find four points (2V 2I) far enough apart to give decent accuracy when squinting at the scales.

In this case of course it's all computer and mouse and line-tool. But same idea: line long enough so you can get good readings of V and I at each end.

Thanks,
i think i got it,so here is another try:

curves for E88cc this time
200V B+
80K RL