Help with Calibration: Hickok Western Electric KS-15750-L1 Tubes Tester - diyAudio
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Old 30th October 2012, 11:28 PM   #1
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Default Help with Calibration: Hickok Western Electric KS-15750-L1 Tubes Tester

I recently got a Hickok KS-15750-L1
I am trying to calibrate it. I attached the operation manual and calibration process and schematic.

The AC voltages are fine.
The Plate DC voltage (#2b) is 214 VDC. It is suppose to be 148 - 156 VDC.
The Screen DC voltage is fine.

Does anyone have any idea what is the problem ?

Could it be a bad 83 tube ?
I tried with 2 different 83 tubes and get the same result.
Attached Files
File Type: pdf Hickok KS-15750-L1 Manual.pdf (832.9 KB, 144 views)

Last edited by HP8903B; 30th October 2012 at 11:33 PM.
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Old 31st October 2012, 12:56 AM   #2
TheGimp is offline TheGimp  United States
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Are you using a variac and setting the filament voltage to nominal?

Line voltage is higher now days and could account for at least half of the difference.
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Old 31st October 2012, 01:01 AM   #3
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One thing to remember, those old manuals specified an analog meter with maybe 10K or 20K ohms per volt. Digital meters barely load the circuit at all.
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Old 31st October 2012, 02:45 AM   #4
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I am not using a variac.
This tube tester has an adjustment for the AC voltage coming in.
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Old 31st October 2012, 02:51 AM   #5
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Quote:
Originally Posted by astouffer View Post
One thing to remember, those old manuals specified an analog meter with maybe 10K or 20K ohms per volt. Digital meters barely load the circuit at all.
That is something I am unclear about.
The manual specifies a 1000 Ohm / volt DC meter.
I have a Fluke 87 V.

Does this mean, the DC voltage readings on the Fluke will be higher ?
If so, by what percentage ?

The manual also specifies to use a 1000 ohm / volt DC meter to measure the Screen voltage.
I use the Fluke and I get the correct reading.
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Old 31st October 2012, 02:59 AM   #6
Bill_P is online now Bill_P  United States
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Quote:
Originally Posted by manp111 View Post
I am not using a variac.
This tube tester has an adjustment for the AC voltage coming in.
The meter input impedance is causing the problem. The calibration procedure specifies a 1000 Ohm/Volt meter and yours is probably 10 Megohms. Connect a 200K resistor from the meter plus to minus terminals and try the measurement again.
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Old 31st October 2012, 03:20 AM   #7
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Could you explain the purpose of the resistor ?
Also, how did you come up with 200K ?

Just to make sure I understand you correctly, I put the 200k resistor in between the + and - probes of my Fluke meter ?
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Old 31st October 2012, 03:25 AM   #8
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Quote:
Originally Posted by Bill_P View Post
The meter input impedance is causing the problem. The calibration procedure specifies a 1000 Ohm/Volt meter and yours is probably 10 Megohms. Connect a 200K resistor from the meter plus to minus terminals and try the measurement again.
I tried that. I had to put 2 resistors in series to get 200k.
I get a reading of 150 VDC.
The manual specifies 148 - 156VDC.
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Old 31st October 2012, 03:31 AM   #9
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I also measured the Screen voltage with the 200k resistor.

The voltage is within specs from the manual. I am surprised.
The 200k resistor only drop the voltage of the plate, not the screen.

With the 200k resistor, both Plate and Screen voltage are in specs.
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Old 31st October 2012, 03:43 AM   #10
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Quote:
Originally Posted by manp111 View Post
I also measured the Screen voltage with the 200k resistor.

The voltage is within specs from the manual. I am surprised.
The 200k resistor only drop the voltage of the plate, not the screen.

With the 200k resistor, both Plate and Screen voltage are in specs.
The screen current is very small so you probably won't see much drop using the resistor.
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