My new RCA CTC-25!

[Electronic M]

Break the cathode ground connection on the H output tube, connect an ANALOG current meter set to the 0-250mA or 0-500mA scale, and adjust the H. linearity/efficiency coil with a PLASTIC diddle stick for minimum current current reading possible. That reading will likely be in the 185-225mA range. Sam's manual should have typical value in the schematic and max listed under the H adjustment procedure. As long as it is below max by at least 10mA you should be good long range. Adding a 1/4A fuse between the cathode and ground while doing the measurement is a good idea, and if mounted topside will facilitate future current checks. Report back the number and record the number so you have a referance if it changes in the future.

Two things to beware of on CTC-16 and later chassis with that style of flyback tire are 1.) some HV rect tubes are too short so the glass of the top does not fully seat against the fly causing damaging arcing, 2.) if the brown part of the tire starts to turn black (what I see in your pic looks fine) between the HV tube top cap and fly core then the tire is becoming conductive and allowing damaging arcing....If that occurs peel the brown rubber off (best done when the fly is warm from running if it can still safely run and produce HV) any skin colored silicone in the blackened area any char on the windings (be careful not to go too deep), and re-coat the HV winding with silicone. Check both the front AND back rubber for blackening as it does not always get both sides at once.