Hello;

I was checking the calibration state on a Hickok 752 and the 'normal
position S5' plate voltage is at 189 volts instead of the normal 150
volts. When I press the the 'low plate voltage S4' switch, the low
plate reading is around 69 volts - 68 is the calibrated norm.

All other voltages are within tolerance, including all the filament
voltages.

According to the manual, the only thing that can cause a high plate
voltage is to high of a voltage on the primary of the power
transformer. This is not the case.

I do notice that when I switch the meter to AC, I am getting around 24
vac when I do both the high plate test as well as the low plate test.
When the plate switches(S4 & S5) are not yet pressed, there is AC at
the plate of around 9vac.


Any ideas?

Thanks in advance

Hi,

I was checking the calibration state on a Hickok 752 and the 'normal
position S5' plate voltage is at 189 volts instead of the normal 150
volts.

Try shunting your meter with 250k and repeating the measurement.
There's a small capacitor that's charging to the peak of the waveform,
without any load.

73, Alan

Hi Alan;

Never thought to look at the ohms/volt rating on the meter. The manual
specifies a 10Kohms/volt meter. Your suggestion makes a huge
difference. My readings are normal now.

One other question regarding the multiplier. When I have a low scale
reading on x4, I switch to x2 to get a reading closer to center scale.
The readings are close, however when I go to x1, the reading is
extremely low. If this is scaling the meter, my x1 is closer to x5. Am
I correct to assume that my x1 position is wacked?

The only thing else I noticed it that the bias fuse is a type 44
instead of a type 49.

Thanks for your time

Hi,

One other question regarding the multiplier. When I have a low scale
reading on x4, I switch to x2 to get a reading closer to center scale.
The readings are close, however when I go to x1, the reading is
extremely low. If this is scaling the meter, my x1 is closer to x5. Am
I correct to assume that my x1 position is wacked?

It's probably fine, but I don't own a 752 or have a schematic
handy. I wouldn't assume that the ranges scale properly.

The only thing else I noticed it that the bias fuse is a type 44
instead of a type 49.

Bad news: the 49 is there to protect the unobtainable bias pot if
you test a shorted tube.

73, Alan