Hi Dick,
Thanks for your response. I was tuning the amp on and off about 10 seconds
at a time. It seemed to tune up fine - then bang and no ip or ig on the
meter. The crazy part is, you would think were ever that arc came from
would have at least carbon trails or some fusing - but nothing! The hole is
pointing right at the plate RF coke, but not even any discoloration is
noticeable. I ordered a new plate RF choke from Ameritron anyway - due to
previous comments about the original being somewhat resonant near 17 meters.
The hole in the tube is remarkable. I've been haming for 38 years and I've
seen cracked glass before but not a hole with flowing glass!
Doug -- W4DXV
----- Original Message -----
From: Dick Green <dick.green@valley.net>
To: Doug Person <w4dxv@ibm.net>; amps <amps@contesting.com>
Sent: Friday, June 11, 1999 12:53 PM
Subject: Re: [AMPS] Finally - a real amp
>
> > 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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>
>
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