[Tomcomm]

Hi Members...........I have returned back to my 21TC55 "lab test bed" after about six months of doing other techi stuff. When I turned it on
about two weeks ago it came right up but was totally out focus due to CRT blooming. I checked all the standard operational readings I use
for setup: Room Temp=60deg, AC input=115vac, B++=424V, FBI=200ma, boost=770V, ultor=30KV, focus=5.4kv, all normal for this
"experimental" setup. After one hour running, RT was 70deg, AC=115, B++=415V, FBI=199ma, boost=800V, ultor=32KV, focus=5.8KV.
No CRT blooming, fine picture. I measured the CRT heater voltage direct at socket with a true RMS Fluke DMM. It read 6.16vac. I installed
an old CRT booster that raised the heater to 7.64vac. The neck was much brighter of course, so I left the TV on for only a couple of hours.
The set was running at 2% under spec heater all these years and now it was running 20% over spec for two hours. I turned the set off.

Nest morning at 7am, RT was 54. I powered up with booster off, the 21CT55 came up with no bloom in perfect focus! Readings were AC, 115V, B++, 420V, FBI, 200ma, boost, 860v, ultor, 33KV, focus, 5.6KV, heater read 6.01vac. After about 4 hours running with fans off, RT, 74deg, Ac, 115vac, B++, 422, FBI, 190ma, boost, 780v, ultor adjusted to 30KV, focus, 5.7KV, heater, 5.93vac. No blooming, good picture so I measured the FBX temp with digital thermo meter applied direct to primary and EHV secondary. Max temp was 112deg, barely warm!

Pleasant surprise, the CRT shutoff uniform glow problem was greatly reduced, almost unnoticeable! Could it be the 21FBP22 running low heater all these years allowed contamination to build-up on the cathodes causing loss of emission and/or causing grid emission that produced the glow? In-the-day the CRT boosters were quite poplar for restoring brightness and were left in place running at close to 8vac which shortened CRT life considerably. I always took them off after a few days/weeks, often with no noticeable decrease in brightness or increase in blooming.

I still have this problem with the hybrid combination of original CTC2B horizontal oscillator and 6CB5 HOT driving a CTC16 flyback xformer and
associated components, driving the original CTC2B yoke. This mismatch works fine but since it has no width control and only limited centering control, the screen is over scanned about 2 inches and is off center about 1 inch. This is unnoticeable except on test patterns.The BIG problem is the very noticeable horizontal video "fold-over" on the left screen presumably due to the horizontal sweep flyback starting up before the previous field's
video is blanked? The magnetic horizontal deflection of color CRTs is probably the most heavily engineered, most critical component matching
requirement, highest efficiency consumer electronic system of the 1950s. It obviously does not permit the "hacker" approach to customizing I usually pursue. I've tried all the usual modifications using all combinations of resistance, capacitance and inductance to reduce the horizontal width
and enable horizontal centering with no success and almost tragic results. Soooo, I am now designing a video blanking circuit that cuts off the foldover contaminated video for the first portion of every video line. It starts immediately after the chroma burst and extends three microseconds which
completely removes all visible traces of video foldover from the screen. Once I get this circuitry installed into the CTC2B under-chassis I will do a painful optimal convergence and be ready to take a batch of screen shots with Judy's new Sony DSC-HX9V 16.2 mega pixel pocket camera.

The CTC2B with "gray screen" 21FBP22A CRT combination has an extreme dynamic range that displays to the human eye details into deep shadows that our other cameras failed to capture. Hopefully, the Sony camera has a greater low-light dynamic range?

The video gate module is now installed, works perfectly! I'll probably do a convergence tomorrow and if I survive I'll take some screen shots with the Sony..........Tom