Quote:
Originally Posted by old_coot88
'Blooming' occurs when the high voltage drops signifigantly. Static attraction from the front of the CRT decreases, allowing sweep angle to increase or "bloom". The raster progressively dims and goes out of focus as it blooms.
The most common cause is a weak HV rectifier. Or excessive CRT beam current can lug the HV supply down (eg., from the brightness control being turned too high).
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Here's 4 pages from the RCA HB-3 Tube Manual showing the specs. for the 5TP4 CRT.
The limiting factor for this tube is that it can only dissipate 5.4 watts. This is determined by multiplying the Ultor operating voltage ~~27,000 volts by the beam current ~~200 microamps.
If this value is exceeded for a long time the heat developed can crack the faceplate. This results in what RCA laughingly calls a "catastrophic failure" of the CRT.
You can measure the beam current by connecting a 1000 ohm resistor in series with the cathode lead to ground and measuring the DC voltage across it. 200 microamps [0.2MA] would show a voltage of 0.2 volts.
It is always gratifying to see these projection sets restored because they represent an important step in the development of television.
Your restoration is specially interesting because you have done so much work
and very well to make this set look and operate like new again. Congratulations.