>> >>In FM broadcast service, 8281/4cx15,000As emit blue light through the
>> >>anode insulator. However, this phenomen can only be seen when no
>chimney
>> >>is used in the design.
>> >>
>> >Must be from some kind of corona discharge from the HV. It cannot be from
>> >tube/element heat if it is blue. Is ordinary corona blue?
>> >
>> / As I understand it, when high velocity electrons strike the ceramic
>> insulator, they bump its electrons up into a higher orbit. When an
>> electron slows down and falls back to its original orbit, it emits a
>> photon -- i.e., the ceramic fluoresces. A similar blue glow occurs when
>> electrons strike some types of glass.
>>
>
>
>I used to own a W1SL 2 x 4CX250B amp for 144MHz many years ago - was
>operating MS one night in total darkness (pretending not to be in because
>neighbours in other flats/apartments might have a BCI/TVI problem) and I
>noticed a similar glow.
>
>When keyed the amp I had two blue patches of light on the ceiling which
>were modulated in brightness with the RF.
>
>Originally the amp had a pair of GE '250B's (the ones with the purple
>ceramic)
>later replaced with a pair of Eimac '250BMs - still emitted light but not as
>much. No excessive anode voltages we used (2300 off load, about 1950
>on load) and always acheived sane/sensible power out.
>
>Never decided if it was the ceramic or the PTFE I used for the chimneys
>that was fluorescing...
>
The PTFE in my 432MHz amplifier does not fluoresce.
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
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