Eico 666 Tube Tester Buries the Needle

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streetcore

Member
Joined 2009
#1
I picked up an Eico 666 Tube Tester yesterday and tried testing a few tubes today. First were two 6U8 tubes. I read that the roll chart was unreliable, so I downloaded the Tube Data Chart dated 1-1-78, which I believe is the most up to date. The initial leakage tests seemed to go as expected, but when I did the merit test the needle went right off the Good side of the scale and was buried or pinned on the right side.

I repeated the same test using the settings on the roll chart. There are two lines for the 6U8 tubes and on one line I got Merit reading in the middle of the Good scale, but on the other line the needle went off the scale again. Same thing happened with both tubes.

I probably should have stopped there and asked for advice, but I decided to test some 7591 tubes next using the 1978 chart settings since the 7591s are not on the roll chart. This time tester seemed to function normally providing Merit results around 120-130 for four tubes.

Lastly, I tried a 5AR4 tube and the needle was buried on the right side again.

Is there a problem with this tester or am I doing something wrong?

Thanks.
 
#5
 
#6
Thanks for all the links. I've seen a lot of them and downloaded the manual and other documents before deciding to make the purchase. I'll try and do the calibration and see if that helps. Seller said I could return it within 7 days if it wasn't working properly.
 
#9
I tried to do calibration tonight, but didn't get past first step. I set voltage to 130, then pushed C button and touched cap lead to chassis, and the needle moved toward "0" on inter-element scale, but didn't make it all the way. It stopped at about 130 on upper scale as seen in attached pic. So I tried adjusting R7, but nothing happened. I moved the knob throughout the full range, but the needle didn't budge.

I then measured the resistance across the centre and outer pins on R7 and the resistance changes when I turned the knob. So it seems it seems to be functioning, but maybe not properly. The document by Mike at MDBVentures.com suggests cleaning or replacing the adjustable resistors if unable to zero meter, so I'll try cleaning first.

Any other suggestions would be much appreciated.

Thanks.
 

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#10
Well, I feel like an idiot. 🤦‍♂️ I had the calibration pots mixed up. After taking the tester out of the case I put it face down to figure out where everything was. Then I flipped it over and was having a hard time connecting my voltmeter at the back, so I turned tester around so I was looking at from the top down with the meter closest to me. I was thinking R7 was on my left side, but it was actually on my right side.

Before I figured out what I was doing wrong I cleaned the calibration pots and replaced two 270K resistors that were measuring 320-350K. Then I tried calibrating again and it still wasn't working, because I was still looking at the tester upside down. I went back to the "Buying, Restoring, and Calibrating" document and then to the schematic when something clicked and it suddenly dawned on me what I had done.

Now it is calibrated as per the manual and I tested the two 6U8 tubes again. On the first one the needle went all the way to 140 on the end of the GOOD scale, but it didn't go past like it did before. The next tests where fairly normal, around 120-130.

I still need to do some more testing and read through all those documents, but at least now I feel like it is working reasonably well and I don't need to worry about returning it.

Thanks to everyone who offered advice.
 
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