[Tomcomm]

When I first got my 21CT55 operational about a year ago, I replaced the two huge selenium rectifiers with a couple of 800PIV, 20A silicon diodes. This raised the 400v B++ buss from a sub normal 390v to supper normal 420v when operating from my local 115vrms mains. Everything worked OK, but I set my Powerstat down to 110vrms which lowered the B++ to 400v. It remained at 400v for all my convergence setup, picture quality evaluations and screen shots. the power transformer's surface was 124F at room temp of 77F.

I never had access to a HV probe for my VTVM so I always ran the Ultor control fully cw max. No problem with focus and the 6BD4 HV reg was running dark as expected. Last week I got two hi voltage spiral film resistors that added up to 940Meg. I was able to calibrate my VTVM to 4v on the 10v range when touching the probe to the 400v B++, indicating I now had a 100 to 1 voltage divider. I read the "boost voltage" at 980v without the probe and 9.7v with probe which translates to 970v or 1% low. I then touched the probe on the Ultor capacitor and got a reading of 34KV ! RCA specs the 21FBP22 at 27.5KV max. I checked the focus at 5800v. Sams and RCA sets the Ultor at 25KV, so I reduced mine to 25KV and had to refocus to 5200v but the convergence, both static and dynamic was way bad.

There is no X-Ray shielding or safety glass on this TV since 1964, when I destroyed the cabinet in going to vertical chassis. I wonder how much X-Ray I absorbed, if any? I could run the CRT between 25KV and 28KV but I must do a complete re convergence which is a real pain. Maybe the 34KV was causing the slight screen cutoff glow by activating the aluminized phosphor and reducing the ultimate black level in dark scenes ? Any suggestions?