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 Post subject: tube testing question
PostPosted: Feb Sat 16, 2019 7:13 pm 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 746
Location: Elko, MN.55020
Have a question that has always bugged me about testing tubes.
I have a couple Hikock testers that have voltage setting dials.
Have always wondered what the correct voltage setting should be used for testing tubes
Can set from 105v to 135v.
My other Hikcock tester shows a red mark on the voltage scale at about 100v.
What voltage should be used to get an accurate reading on these Hikcock testers?
murf


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 Post subject: Re: tube testing question
PostPosted: Feb Sat 16, 2019 9:00 pm 
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Joined: Feb Sat 06, 2016 1:47 am
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Location: La Mesa Califonia
Line set to 120 volts with tube being tested in socket.


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 Post subject: Re: tube testing question
PostPosted: Feb Sat 16, 2019 9:17 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12336
Location: Mpls, Minnesota
The voltage readings around the knob simply give you a rough estimate of the incoming voltage when the line adjust is set correctly on the meter, as these markings are rather useless many testers do not have them. On the testers withe the separate voltage meter, adjust the voltage to the red dot. Read your manual carefully, some want you to do the line adjust before inserting the tube, some want you to adjust after inserting the tube.

Dave


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 Post subject: Re: tube testing question
PostPosted: Feb Sat 16, 2019 11:53 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18297
Location: Albuquerque, NM 87123
If you have not been adjusting this control you have probably got somewhat erroneous readings on all the tubes you tested. That control adjusts the filament voltage going to the tube. If it is set high then too much current is going to the heaters and you may get higher emission and possibly a gas or leakage indication. If it is set low then you may get lower emission results.

When the tube tester is calibrated correctly it will deliver proper heater voltages when adjusted to the Line Set position. This control is needed because heater/filament currents vary widely.

As a test, you should check filament voltages once in a while with an accurate AC voltmeter under load while testing a tube.


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 Post subject: Re: tube testing question
PostPosted: Feb Sun 17, 2019 11:50 pm 
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Joined: Jan Wed 11, 2012 4:21 pm
Posts: 746
Location: Elko, MN.55020
I have adjusted accoeding to the red dot on the scale on the one hikcock tester, and just set it to the 120 volt setting on the other Hikcock tester.
Get different readings according to the tester used. Noticed if I dial the voltage back to 100 volts where the red mark is on the other tester, the readings show higher on on the tester without the red marking on the scale.
Just don't know which is more accurate.
murf


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 Post subject: Re: tube testing question
PostPosted: Feb Mon 18, 2019 12:21 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 12336
Location: Mpls, Minnesota
What are the model numbers of your testers??

Dave


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 Post subject: Re: tube testing question
PostPosted: Feb Mon 18, 2019 3:02 am 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8258
Location: Long Island
Surely you've heard of Segal's Law: "A man with one watch always knows what time it is. A man with two watches is never sure." Trying to get two tube testers to agree with each other is a similarly hopeless situation.

Most--but not all--Hickok power transformers were designed to give nominal output voltages with 106 volts input, after the line adjust rheostat. That's where the red mark usually is in models with separate voltmeters. It seems unlikely that the meter on your one tube tester would have no red line or dot for setting the line voltage, so maybe it is a replacement. If so, its calibration could be iffy.

What you need to do is find out where the voltage needs to be set to get proper heater voltage to the tubes under test. Easiest way to do this is to plug in a tube which draws a bit of current. A 5U4 would make a good candidate, but you could use just about any power tube with a 5, 6, or 25 volt heater. (Most tubes with higher voltage heaters don't draw as much current). With the tester set up for the tube of choice, plug the tube in and measure the heater voltage after giving it 20-30 seconds to warm up. It should be within a few percent of the nominal heater voltage rating of the tube if the line voltage control is correctly set.

Once you figure out how the line voltage control needs to be adjusted for that tube tester to operate correctly, the tester should be okay to use, assuming it's in reasonable condition. But don't expect to get exactly the same reading on the same tube from two different testers. That's not going to happen except by accident, even if both testers are Hickoks. However, you should find that if a tube has an internal defect or is worn out, every tube tester should flag it as bad.

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


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 Post subject: Re: tube testing question
PostPosted: Feb Mon 18, 2019 3:12 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18297
Location: Albuquerque, NM 87123
Until your tube testers are calibrated you are only guessing.

As I stated before, you will not know what voltage is being sent to any tube filament unless you test with an accurate AC voltmeter. You need to get some tube specification manuals so you know EXACTLY what voltage a filament needs. Until you do this you are wasting your time.


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