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Old 29th Jan 2010, 1:47 pm   #14
Leon Crampin
Octode
 
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,869
Default Re: Magic eye valve types

If you're testing an eye on a valve tester there's no need for an anode resistor. As long as you separate out the two supplies for the anode and target (I use the screen supply for this), you can make the eye "work" just by adjusting the triode anode voltage on the tester. As the deflection electrode is directly connected to the triode anode, this is a perfectly valid check and replicates what happens in use.

You can test the triode as you would any other triode, first. Magic eye triodes usually have fairly low gms of about 1 mA/V. This figure is never given in the data, but I've tested so many this way I know what to expect.

Sadly, it's always target degradation which kills an eye - I've never seen a faulty or even low emission triode. I haven't thought of a fix for this yet...

Leon.
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