Hickok calibration

[famousmockingbird]

Ok so when my Hickok 539b tube tester is on the red "test" line on the AC meter my plate, screen, and grid voltages are a bit on the high side. When I adjust the AC meter a couple increments back (I believe the red line is 100v) making it 95v all of my voltages are perfect.

So is it wrong for me to just set the AC meter to 95 instead of the 100 (red "test" line) when testing tubes because it is more accurate?

I am assuming I have to do this because my house voltage is always high 123v.

 

[HollowState]

Since none of these testers are regulated, they tend to be somewhat spungy in use. Hickok is not always specific here, but I usually set "red line" when pressing P4. If your measurments are taken without a tube under test, they will be higher assuming everything else is correct.

 

[famousmockingbird]

I think I know what I am doing wrong. I need to use a shunt resistor to compensate for not using a 1000 ohm voltmeter.

So to measure 150v I think I need to use a 150k shunt resistor? I believe the shunt resistor is placed in parallel with the input of the digital voltmeter?

I will hold off until someone more experienced can advise to proceed.

 

[famousmockingbird]

I found a PDF by Daniel Schoo on calibrating the 539c.

"Use this procedure to test and calibrate the Hickok Model 539C mutual conductance (AKA
transconductance) tube tester. Except as noted, all of the readings are taken with a 1000 ohms per volt
meter. If an accurate 1000 ohms per volt meter is not available a modern high impedance analog or
digital voltmeter can be used with appropriate shunt resistors in parallel with the input to simulate
proper loading. The following resistor values should be used: 10 volt scale use 10K, 50 volt scale use 51K,
250 volt scale use 250K. All resistors are 1/2 watt 5% carbon composition. Calibration will be easier if
you supply AC power through a constant voltage regulation type transformer to do the tests, but this is
not essential. Recalibrate the tester any time either rectifier tube is replaced. The correct type #81 (#63
for 230VAC mains) fuse lamp must be installed in the tester or false readings can result. "

He says put the resistor in parallel with the input. I guess I am still confused on where the resistor goes. Parallel makes no sense to me and I still get the same reading. I also tried in series with the voltmeter and I got the same reading.

I am reading 167vdc at the plate pushing P4 with 6l6 settings and the ac meter on the "test" red line. Is this way to high? I noticed that there is no adjustment for plate voltage in Daniel's article.

I want to mention that I get 260mVAC at the grid with the ac meter set to red line.

All measurements were taken with a modern digital multimeter.

 

[kevinkr]

Place the resistor mentioned in parallel with the input of your DMM. Its purpose is just to make the DMM look like an analog 1kohm/V multi-meter. This will not matter for some measurements and will be important for others. (Ones measuring nodes with significant source resistance)

 

[mksj100]

When using the older multimeters the resistance of the meter in the circuit, was a fixed amount depending on the voltage range selected, not the voltage read. As if placing a resistor from the cathode to the anode or - to +. If this load is not present, the voltage readings can be substantially higher when using a DMM which usually have an impedance of 10mohm or greater on all scales. So for comparison on the plate voltage I get around 190V when measured with a DMM (unloaded), around 151V with a DMM & 250K resistor attached between the + and - leads while measuring the plate voltage (simulated 1000 ohm/v) and 149V using an AN/PSM-37 on the 1Kom/V range and 250V scale. You must set the line voltage at the red line (100V AC), as this effects all the voltages in the tester (plate, screen, heater and signal). If these are not set correctly you can get some fairly erroneous readings. Additionally a slightly higher/screen voltage have a small impact on GM readings vs an incorrect signal voltage, and there is no adjustment for the plate voltage anyway. You also need to make sure your plate balance for the 83 and 5Y3 tubes are set correctly and the signal voltage is correct. These significantly effect the GM readings if off. Additional info:
Antique Radio Forums • View topic - Updated Hickok 539 Calibration document
http://www.amplitrex.nl/wp-content/uploads/Hickok-539C-Calibration-AudioXpress.pdf

If your plate, screen and signal voltages are high when measured with a properly loaded DMM, I would check the calibration of the AC voltmeter/line voltage. It may be that your AC voltmeter is reading low, so when set to 100V you may be getting something like an actual 105V. You can also press the P7 on the tube tester to give actual line voltage and see how that compares with your DMM.