On Fri, Sep 11, 2009 at 01:09:33PM +0000, Paul Decker wrote:
> Thanks to all that replied. At this point, I think a tube has gone
> bad. Removing the "bright" tube, the amp can be loaded up and produces
> output. Swapping the sockets, the problem seems to follow the tube.
>
> As was pointed out, I don't have anything to loose with the bad tube.
> There was some talk about "blowing the short out". I don't have a
> 400VDC supply, but I guess I could rectify a 240 VAC line, that would
> get me about 380 VDC @ 15 amps. Another suggested a car battery. I do
> have an adjustable60 vdc @ 60 A current limiting supply available.
> Would I just put this to the heater pins?
It's good that you're able to move the trouble with the tube.
First, ohm the tube out, each pin and the plate cap to each other pin
and the plate cap; record the results -- or have someone else record the
results while you move the test leads around. You want to put the voltage
across any connections that don't show in the tube's schematic, but Google
first to see if there are any "factory-use-only" internal connections that
you don't want to blow away. All this is "obvious", of course,; that's why
I'm mentioning it: I'm good at not seeing the obvious sometimes.
Heater pins are a special case, as you don't want to blow the heater up
while trying to blow a heater-cathode short away. I don't know what to
suggest there, aside from hooking *both* heater pins together; perhaps
someone else can make a suggestion about this.
Keep in mind that if you do manage to melt or vaporize the material causing
the short, there probably will be a remnant left on each side, raising the
odds that the tube will flash over between those two electrodes at some
point. On the other hand, you have little or nothing to lose at this point.
--
Mike Andrews, W5EGO
mikea@mikea.ath.cx
Tired old sysadmin
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