How to test EML tubes with the AT1000 tube tester.
In the so called stand alone mode, you can not verify EML tubes comfortably. Besides, the tester uses operating points from the stored data table inside the tester, which operating poinst may not be as you need, but you can not change those easily. Changing the data table inside your tester, has a risk to damage the software, and I ecommend you not to do so in the beginning. You would need to send it to Amplitrex for repair if that goes wrong. So much better, and fully safe is the computer mode, as this can use any setting you want. I would say the stand alone method, is not qualified for detailed testing our tubes, only for rough testing.
Computer Mode testing of EML tubes
- First, create a directory on your computer, where you will save the settings that we are going to create.
- Select a tube with the right heater voltage, and generic part number is more or less the same. For instance we are going to set it up for 300B-XLS here, and we will change the 300B settings for this. Note, the change is only in the self made "set up" file that we store on the PC somewhere. This will make no change to the AT1000 internal data.
- Open the 300B tube from the Amplitrex computer test menu.
- In the TAB "TEST SET UP" change the Test setting to what you see on the tube box. That is Ua= 495V. Ia=100mA. Take the Gm from the EML website (it is appr 6300 for new tubes). Enter the Grid voltage as you read it on the tube box of YOUR tube, that you are going to test. It can be from appr 100V, with a few Volts tolerance, but you need to take what you see on the box.
- In the TAB "LIMITS" enter this: Plate max 125mA, Plate max 65 Watt
- Go to the top menu of the AT1000 screen, and enter SETUP, SAVE. Use 300B-XLS as filename, use the directory you made at 1)
- Go to the top menu of the AT1000 screen, and enter SETUP, LOAD, choose the file you just saved, check under SET UP if all data is there
- Plug in the 300B-XLS and switch the heater on
- IMPORTANT: Set the biasing for auto bias.
- Click the TAB "Function" and run the noise test. (No need for the head phone here)
- Watch the AT1000 tester directly (on the green display) and see what the tube is doing. It should go to 100mA now. Observe it, and let the tube warm up for minimum two minutes. Cut and re-start the noise the test when the current is above 115%, so here above 115mA. If you do need to re-start, it means nothing, but the second time the tube should stay stabile. If even not at the third time, the tube is defective.
- Normally the tube will get stabile after a 2 minutes already. Extreme stability is not needed, expect for precision testing. This is called, thermally stabile, and you can now do the test.
- After the tube is run hot, under the noise test program, you can end the test with the "OK" button that should have popped up at starting the noise test. Directly continue with the next test.
- While the tube is still hot, select both tube test and plate curves, and then press start
- RESULTS WILL SHOW UP.
- The result will have a gird voltage. If this voltage is the same as on the box, the tube is good. Deviation can be several volts for a used tube, but the way to just this is another (see next chapter)
Verify USED tubes
This is done in the FIXED BIAS mode (Click the TAB "Function)
- Use the 300B-XLS set up from above
- Go to the tab TEST SET UP and enter the grid voltage of your tube, as you see it on the tube box. Now suppose, it is 99 Volts. So you enter 99 Volts in the menu. The rest stays unchanged.
- Click the TAB "Function" and set it for FIXED BIAS
- Goto to10) from above here, and finish the testing.
- The result will be the PLATE CURRENT. You can express this in percent yourself. At 80mA it is 80%. A tube with 70% is regarded good, below 70% it gets questionable, below 60% the tube is worn out, but might still work. Some amplifiers can be very tolerant and work at no problems on a 40% tube, though any amplifier must work perfect on a 70% tube. (This is not 70% emission, but 70% plate current of original, and such a tube at the right Bias will easily supply full plate current)
For all other tubes it works the same, so you should make a small directory with test set ups, and with that you can work quick and convenient. Note the right heater voltage. You can change that with the set menu. For instance if you make an adapter for the AD1 tube, which you want to plug into the UX4 socket, you can begin with the 2A3, modify that at 4V and save it as "AD1".