View Full Version : kcs 47a doorknob cap


rcaman
04-06-2003, 04:30 PM
recapped this thing last year. just now getting back to it.
fired the set up and it had a dim out of focus picture. was only getting 8,000 volts to anode. removed the doorknob cap. it was hot. now a i have a bright picture. do i need to replace this or just leave it out. i also have no audio any pointers on this chassis.
thanks steve

Rob
04-06-2003, 04:56 PM
Steve,

You won't hurt anything but possibly picture quality by leaving that doorknob cap out of the HV circuit. I'd replace it if it was my set. I gather you have a metal shell CRT? I have some sets with that chassis but little experience on the bench with them yet. Can't help with the audio question.

Rob

wvsaz
04-09-2003, 03:36 PM
In all-glass CRTs, the internal 2nd anode coating in combination with the grounded external aquadag coating form a high voltage cap to ground, about 500 pF. This filters the rectified output of the 1B3 (half-wave DC pulses at 15,734 KHz) to steady DC.

In a metal shell CRT, there is no "capacitor", so a 500 pF doorknob was added externally to perform the filtering function. Leaving it out is similar to leaving out an electrolytic in the B+ supply, although the "hum" produced will be at H frequency and will affect only the CRT.