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Old 30th December 2012, 10:09 PM   #1
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Default Tube tester

I don't have any experience with tubes but have repaired a few tube Guitar amps. I have A tube microphone and a few tube microphone preamps. I have access to a tube tester for a good price. Would it be useful to me for maintence or diagnosis? Does a tube tester only test good or no good? Can a tube tester be used to match tubes or check other variables? This one has an analog meter on it.
Thanks
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Old 30th December 2012, 10:49 PM   #2
6L6 is online now 6L6  United States
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When is it ever bad to have more tools at your disposal?

It depends on what kind of tester it is, some are just a general tube strength meter, some give much more specific numbers, and then you can match.
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Old 30th December 2012, 11:41 PM   #3
kevinkr is offline kevinkr  United States
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Tell us what it is you have access to and we might be able to better advise you.. IMO emission type testers are worthless so you should be looking for one that states it tests transconductance aka mutual conductance. Gas and shorts testing capability is a bonus.
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Old 30th December 2012, 11:41 PM   #4
TheGimp is offline TheGimp  United States
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What make and model tube tester is it?
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Old 31st December 2012, 12:20 PM   #5
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Quote:
Originally Posted by argonrepublic View Post
I don't have any experience with tubes but have repaired a few tube Guitar amps. I have A tube microphone and a few tube microphone preamps. I have access to a tube tester for a good price. Would it be useful to me for maintence or diagnosis? Does a tube tester only test good or no good? Can a tube tester be used to match tubes or check other variables? This one has an analog meter on it.
Thanks
Hi,
This is an attempt to make a simple tubetester for the most common E-types as EL84, EL34, KT88, ECC81,82,83 , 12BH7 and 6SN7...and more types later. You can find the test setup at my amateur site:

TUBEAMP ...on the site look for "Tubetester" and datasheet for Telefunken, M-O Valve, GE, Siemens & Halske, Sylvania a.o.

The test setup should be able to tell you whether the tube has gas leak , and whether you have 100% emission. Microphonic tubes can be found by knocking on the glass...you will have a ringing-sound.

regards
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Old 31st December 2012, 12:44 PM   #6
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Quote:
Originally Posted by Leakstereo20 View Post
Hi,
This is an attempt to make a simple tubetester for the most common E-types as EL84, EL34, KT88, ECC81,82,83 , 12BH7 and 6SN7...and more types later. You can find the test setup at my amateur site:

TUBEAMP ...on the site look for "Tubetester" and datasheet for Telefunken, M-O Valve, GE, Siemens & Halske, Sylvania a.o.

The test setup should be able to tell you whether the tube has gas leak , and whether you have 100% emission. Microphonic tubes can be found by knocking on the glass...you will have a ringing-sound.

regards
Nice one, thanks for that.
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Old 31st December 2012, 01:34 PM   #7
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Quote:
Originally Posted by Stefkorn View Post
Nice one, thanks for that.
You're welcome,

As the Gm and Mu is understood:

Someone mentioned Gm for tubes :

Transconductance is termed as the change of the current in amperes of the anode for each volt we change the voltage on the control grid, with all other factors held constant.
In other words...if we have the setup I mentioned from my amateur site with two variable voltages ...one 0-300V for the plate, one neg. 0--120V for the grid, it is possible to draw the Gm lines on a datasheet paper... by change of the negative voltage of -1V step by step. I know it takes some time....
Mu = gain
The gain in Mu, describes an voltage change in volts at the anode for each volt we change the voltage on the control grid, with all other factors held constant.
In other words:
If we take the 250V dc as reference on the plates and starts with the -7,3V on the grid of a EL84 ...and then we reduce from the - 7,3V with 0,1V / 1/2V step (up and down) it is possible to read and write the platevoltage down on the datasheet....I know it takes some time...

Just a proposal....

regards
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Old 31st December 2012, 03:44 PM   #8
Yvesm is offline Yvesm  France
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Hi,

you write:
"The gain in Mu, describes an voltage change in volts at the anode for each volt we change the voltage on the control grid, with all other factors held constant."

Wich is perfectly true and means the the anode current MUST be held constant.
But the anode current will change when changing grid voltage (as for Gm measurement), so you must readjust the plate supply voltage to restore the same plate current.
It is the value of this "readjustment" wich is the Mu.

Another way is to measure the Rp (wich is Mu / Gm).
This can be done by changing the plate voltage with all other factors held constant while plotting the coresponding current change and you know Rp as dVP / dIP.

Since Gm is already know, you can compute Mu as Rp * Gm.
Because Gm is usually expressed in µmho, Rp must be expressed in Mohm.

Yves.
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Old 31st December 2012, 07:59 PM   #9
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Quote:
Originally Posted by Leakstereo20 View Post
You're welcome,

As the Gm and Mu is understood:

Someone mentioned Gm for tubes :

Transconductance is termed as the change of the current in amperes of the anode for each volt we change the voltage on the control grid, with all other factors held constant.
In other words...if we have the setup I mentioned from my amateur site with two variable voltages ...one 0-300V for the plate, one neg. 0--120V for the grid, it is possible to draw the Gm lines on a datasheet paper... by change of the negative voltage of -1V step by step. I know it takes some time....
Mu = gain
The gain in Mu, describes an voltage change in volts at the anode for each volt we change the voltage on the control grid, with all other factors held constant.
In other words:
If we take the 250V dc as reference on the plates and starts with the -7,3V on the grid of a EL84 ...and then we reduce from the - 7,3V with 0,1V / 1/2V step (up and down) it is possible to read and write the platevoltage down on the datasheet....I know it takes some time...

Just a proposal....

regards

Why bother, I use a XY writer for that, and a 0-300v power supply
set the grid voltage, Pen down sweep anode voltage , Pen up set grid voltage.
it takes about 1 to 2 minutes

cheers, v4lve.
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Old 31st December 2012, 09:44 PM   #10
Hi_Q is offline Hi_Q  England
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Wonder if you guys have seen this?
The uTracer, a miniature Tube Curve Tracer / Tester.
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