What you describe is very common with receiving tubes, especially beam
tetrodes/pentodes. The blue glow on the glass has long been accepted to be
due to electrons hitting impurities in the glass and is harmless.
It has nothing to do with Cerenkov radiation or nuclear reactors.
In transmitting tubes a different type of glass is used and impurities cant
be tolerated at the voltages involved. In a 3-500 my first suspicion would
be gas.
Carl
KM1H
----- Original Message -----
From: Patrick Barthelow
To: km1h@jeremy.mv.com ; tomp@prohigh.com ; amps@contesting.com
Sent: Friday, July 02, 2010 3:34 PM
Subject: RE: [Amps] 3-500Z blue glow on glass
I have seen two types of blue glow in a TX vacuum tube. One, on the inside
of the glass envelope, and another can be seen in the case of 3-500Zs by
looking vertically down between the slits in the folded tantalum plate,
between the filament and the plate. If the blue is there, then it is likely
gas, being ionized by bombardment of electrons in transit to the plate. If
it is on the inside surface of the glass envelope then that is I think
Cerenkov radiation which is produced by the near speed of light electrons
impacting the glass and decelerating. The blue that I saw on the glass was
not bold, more like faint, and had the same color you see in the water pools
that hold waste nuclear fuel rods, and I think of a similar similar cause,
Cerenkov radiation. Hi speed Electrons decelerating down to the speed of
light when encountering materials with slower speeds of light.
Best Regards,
73, de Pat Barthelow AA6EG
> From: km1h@jeremy.mv.com
> To: tomp@prohigh.com; amps@contesting.com
> Date: Fri, 2 Jul 2010 15:24:03 -0400
> Subject: Re: [Amps] 3-500Z blue glow on glass
>
> That sure sounds like gas. You might be able to salvage it by setting up a
> jig and running about 500V and enough positive bias to get the anode red.
> Use plenty of air and let it cook for an hour or so.
>
> Then step the HV to 1000, 1500, etc while adjusting the bias for the same
> anode dissipation and glow.
>
> No guarantees.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Tom Prohigh" <tomp@prohigh.com>
> To: <amps@contesting.com>
> Sent: Friday, July 02, 2010 12:28 PM
> Subject: [Amps] 3-500Z blue glow on glass
>
>
> >I have a tl-922 amp. One of the 3-500Zs had a blue/purple glow on the
> >glass
> > when HV is applied. The other one has no glow. I don't think that this
> > is
> > a problem as the tubes are not gassy. I just want to make sure
> >
> >
> >
> > Thanks
> >
> >
> >
> > Tom - AB3FL
> >
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> > Amps@contesting.com
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>
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