Current in series with the resistor is 280 mA.....well within spec.

Is the resistor still getting really hot? How many volts is it dropping?

jr

Temperature probe on my meter stabilized at around 197 degrees F, but was still climbing very very slowly when I shut it down.

How about current between the B+ terminal (250 volts?) and the rest of the set? Thinking that there could a lot of ripple current on the input to the filter cap that is contributing to the resistor heating (are the filter caps the correct value?) but perhaps the "fee air" dissipation of the 25 Watt resistor is quite low, and 197 degrees is "normal".
somewhat stumped,
jr

Filter caps are at a minimum at least what was in the set, and are all the correct values.

Well, at last reading it was 243V, or 12V low. I haven't changed anything since, and the set's seen barely 15 minutes run time since.

Compare the two videos....the right side, which wasn't filled out, now is. However, the picture's somewhat bloomed:

Before the selenium replacement:

http://www.youtube.com/watch?v=RPSNHOG0TIU

After:

http://www.youtube.com/watch?v=_bUxHpMFG5w

The only thing that's changed between the two videos is the addition of the diodes and resistors, replacing the selenium rectifiers.

Now the only thing that I can think of, from a purely mechanical standpoint (which may be off, but makes sense to me) is that the heat sinks on the selenium rectifiers were massive. In this case, we're asking a much physically smaller component to do the job of two that were much larger. To me, it almost makes sense that the resistor would get really hot just because of that. But I don't know, because I've never done this job before :dunno:

Hoping some others will chime in with thoughts as well.

I just looked up the spec of the resistor, and it seems that it has a temp range of up to 250C. Since 197 F is about 92C, I think this is just normal.

And, since I only read 280 mA on the current draw, I know I'm not overdriving the resistor risking burnout.

Think I'll hard mount it to the chassis and try watching some television for a bit and see what happens.

I suspect that it will be pretty cool with proper mounting... Hope the tv remains stable. Still a question remains about the low voltage and blooming. :scratch2:

Good luck,
jr

Got up at an ungodly hour this morning :) , mounted the resistor, and watched the set for about an hour. I was able to dial in the picture with the vertical height and width controls. Everything is stable, and the set's running fine.

Realize that your 280 mA reading isn't accurate, as it's a pulsating DC, which most milliammeters won't correctly measure. Having said that, it's probably not that far off.

But there is a fair amount of filtering (150uF and a choke) before the resistor and meter, shouldn't the ripple be pretty small at that point?
A better measurement would be to place the current meter in the B+ source lines (255V, 215V and 145V), one at a time and add the results.

jr

The ripple current goes through the rectifier of course, so an ammeter placed there reads the raw rectified current, not filtered at all. Measuring the current downstream simply removes the AC component and isn't a true indicator of the resistor current. (I am assuming the resistor is where it belongs, in series with the diode and not after any filtering.)