Rca CTC-25 overview and help

[Electronic M]

Originally Posted by ZenithNut

Thank you.

Next time I power the set up I want to watch the current draw. I know the watts on it is 350. So the current draw shouldnt be over 3.2 amps or so once the sets warmed up.

I have a fluke 27/fm. How do i hook it up to watch the current draw? Do I put the negative of the meter to chassis ground and then the positive lead on one leg of the line?

Line current and horizontal output cathode current have too loose of a correlation to be used interchangeably.

The cathode current can be measured by unsoldering the ground lead from the cathode pin of the h output tube socket then connecting the meter positive current terminal to that pin and the meter negative to ground (sometimes you should put a .47uF cap parallel to the meter ). The current will be in the neighborhood of 170mA to 230mA DC. make sure your meter has a 500Ma DC scale... I'm not familiar with your meter so check it's specs/manual. Also it is preferable to use an analog darsonval movement meter to a digital meter... it is a high frequency pulsed DC current on the cathode. An analog meter will average it well and be the same instrument that Sam's and the factory used to measure that. Some DMMs may get confused by non constant DC... I have not had that issue, but since I have an analog meter I use it instead of my DMM.... it is better for adjusting the efficiency coil for minimum current than most DMMs since it will show you minute changes that a digital display will hide in rounding to it's smallest digit.

One recommendation when you're done measuring the cathode current connect a new wire to the cathode pin, run it above chassis to a good spot to ad a fuse holder, ground the cathode thru a 1/4 amp fuse. Doing this will help protect the flyback from excessive current, and the fuse holder above chassis will also make a convenient current test point for future measurements... all you will have to do is remove the fuse and connect a meter across the holder terminals.