rafafredd

Testing tubes for gas and leak
« on: April 09, 2005, 01:18:02 PM »
OK. I don´t have a tube tester. How can I go about testing some tubes I´m selling for gas and leaks and shorts?

I built a simple powersupply and I´m matching the tubes for the same plate voltage, but this is as far as I have gone in testing those.

Everyone that bought some are happy, but still I would like to be able to test those for other possible problems before shipping, and also to test other tubes of my collection for my own use in my DIY.

I guess it´s hard for me to find one of those old tube testers here in Brazil, so I´ll have to DIY it, but have no clue about how to test tubes for gas and leaks... Shorts should be easy...


dale116dot7

Testing tubes for gas and leak
« Reply #1 on: April 09, 2005, 09:48:38 PM »
Tube testers basically need to apply voltages to each electrode and measure some other current. So you can measure most things with a few pots, a few meters, and a big switch to move the meter function to different points in the circuit. You'll need to measure grid and plate currents, voltages, and set grid (each of them) and plate voltages easily. Follow the qualification test specifications you see on the Ratheon military tube data sheets - they show leakage currents, noise, etc. tests.

NewYorkDave

Testing tubes for gas and leak
« Reply #2 on: April 09, 2005, 10:02:49 PM »
Radiotron 4 has a good amount of information on tube testing. You downloaded it, right? ;)

One easy way to test for gas is the "grid shift" method. You cut a large-value resistor in and out of the grid circuit while measuring plate current. You could wire up the resistor between grid and ground and use a SPST switch to short across the resistor. The amount of shift in plate current when the resistor is in-circuit, versus when it's shorted out, will tell you if the tube is gassy. That's because excessive gas will cause enough grid current to flow to create a voltage drop across the grid resistor, which in turn affects the bias and therefore the plate current.

The value of the resistor, and the amount of permissible shift, is going to vary with the type of tube.

adamasd

Testing tubes for gas and leak
« Reply #3 on: April 10, 2005, 01:32:29 AM »
Quote from: "NewYorkDave"
Radiotron 4 has a good amount of information on tube testing. You downloaded it, right? ;)


did someone actualy scan that whole thing or is this sarcasm?

adam
so there

adamasd

Testing tubes for gas and leak
« Reply #4 on: April 10, 2005, 01:46:16 AM »
you can buy it on cd...
so there

alk509

Testing tubes for gas and leak
« Reply #5 on: April 10, 2005, 02:04:49 AM »
Quote from: "adamasd"
did someone actualy scan that whole thing or is this sarcasm?


Here's a hint:



:wink:

Peace,
Al.

Lest laziness get the best of you!

adrianh

Testing tubes for gas and leak
« Reply #6 on: April 11, 2005, 04:13:56 AM »
Al
Thanks dude!
I stole that graphic.
It will com in real handy around here!

CJ

Testing tubes for gas and leak
« Reply #7 on: April 11, 2005, 07:04:37 PM »
The best/cheapest way to test tubes is to plug them in and have a listen.
Tap on them with some chopsticks for microphony levels.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

gyraf

Testing tubes for gas and leak
« Reply #8 on: April 12, 2005, 06:20:08 AM »
Quote from: "CJ"
Tap on them with some chopsticks for microphony levels.


..BUT allow the tubes to fully heat (up to 15 minutes) before trying to judge microphonics. Many frame-grid tubes (e.g. ECC88/6DJ8) are very microphonic untill properly heated. Dunno why though..

Jakob E.
..note to self: don't let Harman run your company..

 

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