ln76d

I need to measure G7 output impedance.
Is the voltage drop method sufficient?
Feeding input of the preamp with 1V/1kHz through the 55-75 pF capacitor and measure drop at the output using potentiometer and multimeter or oscilloscope?

Second thing, how to detrmine pentode (wired as triode) output impedance?
I know that EF86 output impedance in triode mode is 15K, but i need to determine  E80F impedance.


abbey road d enfer

I need to measure G7 output impedance.
Is the voltage drop method sufficient?
Feeding input of the preamp with 1V/1kHz through the 55-75 pF capacitor and measure drop at the output using potentiometer and multimeter or oscilloscope?

Second thing, how to detrmine pentode (wired as triode) output impedance?
I know that EF86 output impedance in triode mode is 15K, but i need to determine  E80F impedance.
The voltage drop method is most accurate for 6dB drop, but then it may change the operating point and thus alter the actual value. Using it with lesser drop (let's say 10% sag) is correct in the sense that it does not change the operating point, but is more sensitive to measurement errors. It is necessary to check the signal integrity, because noise can have a significant effect on the measurement.
IMO, the best method is that that consist in injecting a signal into the output via a high value resistor, measuring the signal, and substituting a resistor for determining the value. Again, monitoring the signal integrity (audibly or with a 'scope) is wise; don't forget the loading effects of the measurement device(s).
You have to remember that both these methods will compute a resistive equivalent of the output Z, not taking into account the subtleties of reactive behaviour.
The experiment should be conducted at different frequencies, low, mid and high, in order to evaluate the effect of these reactive terms.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

ln76d

Thanks!!!!

I will try to measure at the weekend.

I wonder, how the microphones manufacturers  measure output impedance?
Anyone know?
Ricardo? Are you somewhere here?
You were working at Calrec, do you know how was specified output impedance for condenser mikes?

Any tips to calculate the output impedance of the pentode wired as triode?

ruffrecords

You need to appreciate that what you will measure, using the methods listed above, is the small signal ac output impedance. This gives you little or no information about the output impedance at high signal levels and absolutely zero information about the driving capability of the the output. So I have to ask, why do you need to know the output impedance?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ln76d

I need it for educational project :D
I'll be measuring frequency response, polar patterns, sensitivity etc. next week.
It behooves me also know the impedance ;)
I do not insist on this method and I know that it has its limitations.
I should have access to equipment and laboratories, so if there's any described better method i'll be happy for informations.
I will try tomorrow or friday to get measurement norm.

ruffrecords

I need it for educational project :D

OK, just make sure in your report you say you have measured the small signal ac output impedance. Just using the term output impedance on its own is inaccurate.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ln76d

I
I need it for educational project :D

OK, just make sure in your report you say you have measured the small signal ac output impedance. Just using the term output impedance on its own is inaccurate.

Cheers

Ian

Of course, if it will be the only method i will use ;)
I hope that i will find something in norms.

Do you know how (or where i could find some tips) for pentode wired as triode output impedance calculations?
I know that impedance depends on many factors, but how it was specified for EF86 (15K)?

ruffrecords

Do you know how (or where i could find some tips) for pentode wired as triode output impedance calculations?
I know that impedance depends on many factors, but how it was specified for EF86 (15K)?

The output impedance of a triode depends on the topology it is used in. I am not aware of their being a specification for the output impedance of an EF86. Can you please show me where in the data sheet this is listed?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

ln76d

Do you know how (or where i could find some tips) for pentode wired as triode output impedance calculations?
I know that impedance depends on many factors, but how it was specified for EF86 (15K)?

The output impedance of a triode depends on the topology it is used in. I am not aware of their being a specification for the output impedance of an EF86. Can you please show me where in the data sheet this is listed?

Cheers

Ian

It isn't specified in datasheet, 15K value is from Jakob site and i found it on some not G7 related topics and sites over the net.
That's why am asking how it can be calculated? As example  G7 circuit will be good enough :)

abbey road d enfer

Do you know how (or where i could find some tips) for pentode wired as triode output impedance calculations?

You may get a rough estimate by looking at the graphs.
http://www.r-type.org/pdfs/ef80.pdf
On page B, you can see, for example at Vgk=-2V, the 170V line shows Ia=10mA, and page C shows Ig2=2.6mA for a total of 12.6mA. The 150V line shows Ia=7mA and Ig2=2mA, for a total of 9mA.
So you get 12.6-9=3.6mA for 20V variation. You may conclude that the internal resistance - also known as plate resistance - is about 5.5 kohms.

As Ian mentioned, this is not the output impedance, which depends on the actual circuit.
You can see that the internal resistance is dependant on the operating point; this evaluation must be done after defining the operating point corresponding to your needs.
The problem with thismethod is that detailed information such as this particular one is not often available.

You can't measure directly the internal resistance of a tube, you can only measure the output impedance of a stage and derive the value using the relevant formula. Indeed, the best is to use a common-cathode or common-grid stage and measure the output impedance at the plate, because the calculation is easier.
« Last Edit: December 02, 2015, 07:58:25 PM by abbey road d enfer »
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


ln76d

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #10 on: December 02, 2015, 08:29:59 PM »
Thank you!!!!!!!

It clarify a lot!

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #11 on: December 09, 2015, 01:21:01 PM »
Hi.
There is very good method to measure output impendance -  connect LCR meter to the mic's output.
LCR meter allows you to measure resistive and reactive part of impendance at different frequencies (usually 100Hz, 1kHz, 10kHz).
Have a fun!

PRR

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #12 on: December 26, 2015, 11:29:23 PM »
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/e/EF80.pdf

*At 10mA*, the EF80 has Gm of 6.8 to 7.4 mA/V, and Mu(g2g1) of 50.

So *at 10mA* 1/gM is 141 Ohms and Ri is 7,042 Ohms.

BUT.

You would never want 10mA inside a mike. That would be a Watt of plate heat.

Page 9 shows a plot of Gm against Ia. Assuming 1mA, Gm is near 1.6 mA/V. Assuming Mu(g2g1) stays near 50, Ri is 31K. Maybe a little lower at the low voltage used in a tube mike.

If the tube is resistor-feed instead of inductor-feed, you must also account for that resistor. As a wild-dart guess, effective source impedance may be 1/3rd (0.2 to 0.4) of the plate feed resistor.

abbey road d enfer

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #13 on: December 27, 2015, 06:07:04 AM »
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/e/EF80.pdf

*At 10mA*, the EF80 has Gm of 6.8 to 7.4 mA/V, and Mu(g2g1) of 50.

So *at 10mA* 1/gM is 141 Ohms and Ri is 7,042 Ohms.

BUT.

You would never want 10mA inside a mike. That would be a Watt of plate heat.

Page 9 shows a plot of Gm against Ia. Assuming 1mA, Gm is near 1.6 mA/V. Assuming Mu(g2g1) stays near 50, Ri is 31K. Maybe a little lower at the low voltage used in a tube mike.

If the tube is resistor-feed instead of inductor-feed, you must also account for that resistor. As a wild-dart guess, effective source impedance may be 1/3rd (0.2 to 0.4) of the plate feed resistor.
But the tube would be operated in triode mode, which justifies the very different result I expose in my earlier post, doesn't it?
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

ln76d

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #14 on: December 27, 2015, 09:56:33 AM »
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/e/EF80.pdf

*At 10mA*, the EF80 has Gm of 6.8 to 7.4 mA/V, and Mu(g2g1) of 50.

So *at 10mA* 1/gM is 141 Ohms and Ri is 7,042 Ohms.

BUT.

You would never want 10mA inside a mike. That would be a Watt of plate heat.

Page 9 shows a plot of Gm against Ia. Assuming 1mA, Gm is near 1.6 mA/V. Assuming Mu(g2g1) stays near 50, Ri is 31K. Maybe a little lower at the low voltage used in a tube mike.

If the tube is resistor-feed instead of inductor-feed, you must also account for that resistor. As a wild-dart guess, effective source impedance may be 1/3rd (0.2 to 0.4) of the plate feed resistor.

Thanks for great post and calculations!

There's  one minor problem ;)

I'm not using EF80 but E80F which is different tube. Is the Philips SQ answer to the EF806 and has nothing to do with EF80.

http://www.shinjo.info/frank/sheets/009/e/E80F.pdf
http://www.shinjo.info/frank/sheets/030/e/E80F.pdf

Right now i'm "fighting" with overall voltages inside microphone.
I changed capsule for k47 style  because  my teflon CK12 seems to be "out of tune"...
Measuring polar pattern characteristics for CK12, with +/-0,5V matched polarisation voltages (lowered to 58V) i get the worse results than with difference of 9V (for 80V) between backplate and rear diaphragm  (for cardioid). 
It looks close to omni in all three patterns...

bockaudio

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #15 on: September 11, 2019, 06:37:10 PM »
 "my teflon CK12 seems to be "out of tune"..."
The white plastic of the AKG "ck12" is nylon. Unless you built your own out of Teflon.

Marik

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #16 on: September 13, 2019, 02:19:09 AM »
"my teflon CK12 seems to be "out of tune"..."
The white plastic of the AKG "ck12" is nylon. Unless you built your own out of Teflon.

Since Nylon has one of the worst moisture absorption characteristics in business that choice of material is quite bizarre (to say the least) from such a reputable microphone maker...

Best, M
Samar Audio & Microphone Design

www.samaraudiodesign.com

The Art of Ribbon Microphones

bockaudio

Re: Measuring microphone output impedance/pentode as triode output impedance
« Reply #17 on: September 17, 2019, 01:50:34 PM »
The melt point of their capsule is that of nylon not teflon, without question. Then again, the capsule does snap together, like a toy. You can rotate the membrane in place. Perhaps a feature for high volume mfg.