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those effect the HV regulation circuit. No reason to suspect them unless you know the HV reg circuit is not working.
To know that you need to test it, using the shunt on the 6Bk4 and see if the current thru the tube varies with HV pot setting AND CRT brightness. You should get between .5 and 1.5 ma current from high to low brightness (raster). this will vary depending on the HV setting, typical is 23-25kv and should hold to within 500v when vari brightness (the shunt tube draws more current when the screen is dark, keeping the HV in check as the CRT load drops. as the brightness increases so does the currrent thru the CRT and the shunt tube current drops, this keeps the flyback HV total current and HV voltage constant).
I don't think you can check them for value in circuit and get accurate results as to how closely matched they are.
I do not recommend replacement unless there is a KNOWN problem in that circuit.
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