> Now that I've gotton your input, I'm sorry to report that while tuning
> the AL-80A on 17 meters with 500ma ip and 150 ma of ig, A somewhat loud
and
> most unpleasant noise ocurred within the amp after which there was no
current
> indicated for either ig or ip. Did I fry the tube?
That's too much plate and grid current. About how long was the amp key-down
before the bang occured?
> Instead, when I
> removed the 3-500z, I first noticed the top inside surface of the glass
had
> a powdery substance on it in pattern not unlike the fins. Then I
discovery
> the really interesting new characteristic of the tube. There was a hole
> clear through the glass as though it had been shot by a high-powered
laser.
> There are fine cracks around the hole and the glass had actually flowed
> inward almost half an inch. Wow. Watch out for 17 meters on this baby.
I'd be interested in hearing the group's theories on exactly what happened
here. Flowing glass? That must take a lot of heat! I can see where the RF
choke would be destroyed if it had a resonance at 17M, but isn't it more
likely that the tube was destroyed by the excess plate current and/or grid
current?
Doug, if I were you I would thoroughly check that amp before installing a
new tube (BE CAREFUL -- HV CAN KILL YOU!) The heavy current drawn during
this event might have damaged other components. In particular, I would check
the plate RF choke, parasitic suppressor resistor, HV power supply, fuse(s),
filament transformer, bias diode, meter resistors, meters, etc. It would be
wise to enlist the help of someone experienced in troubleshooting 3-500Z
amps.
73, Dick WC1M
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