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7CT1N horizontal calibration


EJP
 

This device gives you choice of 0.5V or 2V per horizontal division, and a 10X multiplier. This implies that the voltage at the C/E terminals with the voltage control fully CW should be 5, 20, 50, or 200V, assuming ten horizontal divisions. However the actual voltages are about half of this in each case. I'm using it in a horizontal slot, and there is no calibration procedure for X in this mode, or any internal trimpot for it either that I can see.

The scope's own X calibration is pretty accurate when evaluated with a vertical plugin in a horizontal slot.

Or am I crazy?

EJP


Colin Herbert
 

First: Do you have a copy of the Service Manual, even if just a pdf? If you don't have any kind of Service Manual, get one before you mess with anything. On P 3-3 of my Service Manual, there is a Fig. 3-1, which clearly shows R 90 as "V/Step CAL", so if you haven't seen that I am puzzled.

I haven't studied the schematics, but I have a vague idea of how the device functions. Bear this in mind and that therefore anything that I write may be wrong; I am mainly using logic.

Don't forget that the 7CT1N is a dynamic device and that when working it will be continually changing voltages in order to display results on the CRT screen, so I don't think I would expect to see whatever the volts per division control is set at giving a steady voltage at any point. It seems to me from the Manual that Tek advocate putting the 7CT1N into a vertical compartment to adjust anything, so perhaps that is the best set-up. I think that if the 7CT1N is subsequently placed in a horizontal compartment, the calibration will still be valid, so long as the horizontal and vertical channels on the host scope are properly calibrated. You just need a time-base with an amplifier function (i.e. X/Y) or maybe putting a vertical plug-in into a vertical compartment.

Good Luck with it, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of EJP
Sent: 24 July 2020 10:50
To: TekScopes@groups.io
Subject: [TekScopes] 7CT1N horizontal calibration

This device gives you choice of 0.5V or 2V per horizontal division, and a 10X multiplier. This implies that the voltage at the C/E terminals with the voltage control fully CW should be 5, 20, 50, or 200V, assuming ten horizontal divisions. However the actual voltages are about half of this in each case. I'm using it in a horizontal slot, and there is no calibration procedure for X in this mode, or any internal trimpot for it either that I can see.

The scope's own X calibration is pretty accurate when evaluated with a vertical plugin in a horizontal slot.

Or am I crazy?

EJP


EJP
 

Thanks. It dawned on me about eight seconds after I posted this that there must be a fault, as it used to be accurate. I have fixed it once before in this area, R30 or R32 IIRC. I'm working on locating the fault as time permits.

I'm not looking for fixed voltages, just observing the screen. I have the manual.

EJP