The glow seen through the ceramic of many ceramic metal tubes
(especially big ones) is just optical wavelengths being transmitted
from the filament. Some ceramics allow more than others, for instance
the guys at Burle Industries (old RCA) tell me that they see a lot
more light through Kyocera than Wesgo/Morgan ceramic. I am not
certain this is what peter was referring to. If only seen when the HT
is enegized, then it isn't just the filament radiation.
>From: "peter.voelpel" <df3kv@t-online.de>
>Subject: Re: [Amps] GS35B glowing ceramic TSPA
>I never saw any metal ceramic tube not glowing and I think it is caused
>by the electron bombardment, not by X-ray.
>Even my class A driver, a 4CX350A at 1500V anode voltage does it
>
>73
>Peter
Depending on which impurities are in the ceramic from Russia, Alumina
ceramic has a high secondary electron coefficient of ~8. If struck by
incident electrons, an avalanche can occur with a yield of
secondaries. Its possible that due to the construction of the ceramic
to metal seals in the tube, a triple junction occurs which has a high
negative field gradient at a point. Its speculation, but things like
this can cause odd things to happen near the ceramic seal.
Trace impurities in the ceramic would be the source of the different
colors of light seen.
Tony wrote:
>One thing that I observed that made me question the X-ray option besides
>John's comment about X-ray generation at such low voltages was the fact
>that when I increase the bias the glow will be reduced at the same time
>FROM THE BOTTOM up leaving a glowing ring near the top at minimum
>current. This fact makes me lean towards electron bombardment but I'm
>not an expert on that.
Hmmm, interesting. Whatever the source, it sounds like there is some
focusing going on with the different bias and anode current.
I forgot, someone here recently pointed out how easy it is to measure
tube temperature with a point IR thermometer. Even better would be a
focal plane array IR themographic camera, but those cost more than
most amplifiers. In my own work, I use a Luxtron 750 Fluoroptic
thermometer that has a fiber optic probe. The probes are very
expensive, but you can probably find the main instrument on eBay
these days. They made a number of models, and they are excellent for
determining surface temperatures which immersed in RF or HV. Getting
the probe to stay in place on a surface is another trick, I tend to
use Kapton tape.
That broken GS35B that Tony showed the link to, was really trashed.
Wonder if it had a series R to the power supply? Looks like a lot of
stored energy dumped from the cathode or grid to anode in that tube.
I thought those Russian tubes were coaxial geometry but they look
like planar design.
73
John
K5PRO
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|