[Tomcomm]

John.....I appreciate your concern for my old 21FBP22A and my new Flyback that's used on at least CT16 thru CT20s. I consider my 21CT55 a bench-top test-bed rather than a candidate for the usual chassis restoration including the mandatory complete recap. My stated long term goal for this test-bed is to demonstrate thru screen-shots the picture quality potential of the wide bandwidth I Q demodulation and low-level matrix processes of the CTC2B chassis teamed with what I consider the best roundy CRT, the grey screen 21FBP22A rare earth. Since I don't consider my 21CT55 a sacred icon of early color TV technology, I am at liberty to take reasonable design risks in the crucial horizontal deflection and EHV ultor system. The original 58 year old FBX that failed developed a short in its primary as the result of rotted insulation due to simple old age rather than over voltage in its secondary.

That said, the replacement FBX's secondary is not the universal winding of the original but a uniform wound solenoid stack of at least 30 to 50 layers! It was completely encapsulated in a multi layered rubbery boot to keep moisture out.

RCA used this FBX in the last 6 or 7 CTCs of the roundy series. I've been using it in my 21CT55 since December 2010 at EHV of 25kv to 35kv with HOT currents of 195ma to 205ma. In all cases it's coil temp has never exceeded 120degF with no fan at room temps of up to 70degF and 112degF at room temps of 95degF with a small fan directed at the FBX. The 21FBP22A is rated at 27.5kv max.This was probably dictated by barely detectable X-ray emissions rather then electrical breakdown within the CRT. It too was subjected to the same sustained 35kv as the FBX secondary. Standard high production engineering practices at RCA would not permit fielding of a consumer product without a proven safety factor of at least 20% to 30%. So 27.5KV times 120% says this FBX CRT combo should run all day with an ultor of 33kv! My performance ultor is now 30kv. The 21CT55 produces this ultor voltage with only 200ma current at the B++ fuze location which is the same current as the HOT cathode current.

Since I feel obligated to push the envelope of the 21CT55 I employ continuous monitoring of all critical parameters during all running of the TV. These include mains input held at 115vac, measure of B++ voltage, HOT current, Boost voltage, Ultor voltage, focus voltage and even CRT heater voltage at the tube socket.

Most importantly, I never allow the TV to run with screen display when I leave the room. I have a switch on the chassis that disconnects the B++ into the horizontal section but leaves all other sections active with tubes on. I hope this drone leaves you and miniman somewhat more comfortable that I'm not unnecessarily destroying a 21CT55 I've had since 1964.