Quote:
Originally Posted by marty59
Taking a load of four(!) 5U4's off would sure cool down the p/s transformer and slow down your A/C meter spinning!
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5 volts x 3 amps x 4 tubes = 60 watts heat saved plus the amount of plate heating due to output current load.
In the RCA 1947-1949 projection sets, one 5U4 powered the audio chassis, one 5U4 powered the tuner, sync and video chassis and two 5U4s powered the sweep chassis.
I'd say this makes the slow and even B+ start provided by the tubes more important.
This, plus the fact that the solid state rectifiers produce higher voltage and can carry more current than the tubes, gives a potential for greater damage when anything fails. I intend to retain 5U4s in my sets.
Back in the late 1950s, we routinely replaced selenium rectifiers with silicon ones, and we learned the hard way that while they helped keep a set going during the summer when the line voltage was low, but in the winter when the line was normal or slightly high, they tended to pop electrolytics and we switched from 10 ohm added loads to 100 ohm loads.
Also, sometimes, especially on transformerless sets, the silicon rectifiers generated a traveling wave that crawled up on the screen. One cure was to add a .01 MFd cap across each silicon rectifier. or from the plus side to the ground. I never understood how this worked, but it usually did.
I'll leave cathode stripping question to the theoreticians, but I will comment on one posting about using deoxit type contact cleaner on these sets. Since the extra high voltage on the CRT is very effective in attracting dust, and deoxit type cleaners leave a sticky film on the surface that tends to trap particles, I'd avoid their use and use traditional contact cleaners on any projection set.
James.