Hi,

I am trying to troubleshoot a non working tube tester. All parts look to be good (resistors, caps (?), tubes, transformer), but I can't calibrate it. No good voltages retrieved (on octal socket) when pressing push-buttons on calibration procedure. When probing rectified voltage on 83 and 5y3 tubes, I have ~160V DC and about 80 V AC. This don't look good (?).

The schematic is difficult to understand. I can't really find a reference point to proble voltages. I don't really know what to do.

Help please...

Hi J-F,
The most common problem I have found with tube tested is that the sockets wear out.

Best Regards,

Bill Grimm

That's right... I thought I had properly cleaned all sockets, but they are still intermittants. Will have to replaced them.

What is the acceptable margin of error when reading a voltage in the calibration procedure?

My trusty old 533 is holding up really well. When I got it, I blasted out all the switches and sockets with deoxit, gently retentioned the sockets with a dental pick, and put a tiny bit of WD40 (with a tooth pick) on all the switch bushings. There was a generous supply of excess tolux inside of the case in the back which was enough to fix the rough corners once they were put back in shape with wood dough. That was sbout 5 years ago.

Once you have a tube set up and running, pay attention to the line voltage adjustment and get it right. Higher filament wattage tubes are especially subject to this. This being done, you can test known good ones against whatever you have, and give a verdict. So long as there are no shorts, gassiness, or bizzare results, a low reading should not be an automatic death sentence for a tube.

:That's right... I thought I had properly cleaned all sockets, but they are still intermittants. Will have to replaced them.
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:What is the acceptable margin of error when reading a voltage in the calibration procedure?
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The best reference point for voltages is the cathode connection at one of the sockets. Set it up for a 6L6 and use pin 8 as the reference. All the voltages are full-wave-rectified, unfiltered DC, so there will be a large AC component along with the DC. You'd need an average-reading 1000 ohms-per-volt meter (Simpson 260) to read them accurately, but the chances are, if they're there at all, they're correct. A common problem with old Hickoks is push-button switches not making contact after sitting for a few decades. Many of them have normally-closed contacts, which will prevent things from working if they aren't making.

Forgot to mention, a Simpson 260 can be made into a 1000 ohms-per-volt meter by shunting it with 250K on the 250V range. Then the plate voltage should be 150V and the screen 130V. Grid bias is 0-40V with an AC signal on top of it.

I have finally all voltages, but at +10% average. Is that critical?

Why do I have to use a Simpson 260? My Fluke our my Radio Shack (Micronta) can't do the job? Not shure to understand why.

Else, can I use an old Amproble volt-ohm-milliameter or at least my scope?

Thank you.

:Forgot to mention, a Simpson 260 can be made into a 1000 ohms-per-volt meter by shunting it with 250K on the 250V range. Then the plate voltage should be 150V and the screen 130V. Grid bias is 0-40V with an AC signal on top of it.
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Amprobe not Amproble. It's a volt meter with a needle not digital.

You can use anything but it may not indicate the right voltage unless it's average-reading. The Amprobe will do, and you could calibrate it against a digital meter on straight DC.

Hickoks also are calibrated for a 1000 ohms-per-volt meter (which draws 1 mA). If you use a more sensitive meter, the voltages will be higher since the meter isn't loading them down.

Thanks for all the infos. I think my tester is working correctly now with all help I found here...

The only things to do now, it's to clean all sockets (finish the job I started) and fine tune the 6000 and 15000 ranges, but I don't have any reference tube to see if 3000 range is ok!

Try testing a few new tubes and if they come out about right, the tester is working properly.

I tested some new tubes... 2x 6l6 (same reading, good) and one 83. Is it normal that fuse light comes on when testing this 83? Tube is NOS and was testing low (english mode)... but testes good on another tester (TV-11).

It's possible. You can swap it with the 83 in the tester to find out.

Yes, all the high wattage filament tubes cause the fuse light to glow a little, even a 5U4. Adjust the line voltage pot before you perform the test.

:It's possible. You can swap it with the 83 in the tester to find out.
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