[Boatanchors] re:resistor mounting

Mon, 21 Apr 2003 21:16:46 -0400

Would it not make a lot more sense to use a separate screen supply rather than
to dissipate 100 watts out of a hard-gained 3100 volt supply?
This does not seem like sound engineering practice! Assuming this were indeed
implemented, the 80k resistance must have at least a 2x or 2.5x safety margin.
This would dictate 200 to 250 watt rated dissipation in the resistor bank! Try
4 20k 50watt resistors as a minimum!

I really am not comfortable with this entire plan.
Imagine if one of the regulator tubes develops an open circuit, or anything in
the series string at the bottom end of the resistor bank opens, or a tube is
removed - we now have 3100 volts on the screens minus the drop in the
resistors. A recipe for disaster, or worse.

I suggest stopping NOW, and rethinking this plan.

Arthur Shulman, VE3ZV

WBob wrote:

> 3100-360=2740V across 80K=94 watts. and smoke from a 50 watt resistor.
>
> WBob
>
> [email protected] wrote:
> > I did not explain the situation correctly as one alert listmember
> > mentioned.
> >
> > The circuit has a 3100V B+ line and the 80K 50W resistor taps off of
> > that and then feed a 3 tube (OA2, OB2-OB2 if i remember correctly)
> > regulator to give me 360V for the screens of a pair of 4CX350 tubes.
> >
> > Thats a TMC PAL-500 amp circuit.  Perhaps the resistor coating material
> > had a flaw which allowed it to fail.  Don't know, don't care, maybe just
> > operator error.  Just need to get suitable resistors and/or capabilities
> > to mount a different type, do it correctly and without having to worry
> > about another failure.
> >
> > Thanks again to the listmember who asked to see if the calculations were
> > correct or if i knew what i was doing!!!! hi hi.
> >
> > larry
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> >
> >
>
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