I experienced the same phenomenon with a 1625, if you are familiar with that tube. I also tuned the final to dip (min current) because I used a parallel tank in the plate circuit. ----- Original Message ----- From: "Peter" To: "Microcontroller discussion list - Public." Sent: Tuesday, May 23, 2006 1:07 PM Subject: Re: [OT] Photons > > > On Tue, 23 May 2006, Russell McMahon wrote: > >> Re Chernkov / Cerenkov radiation. >> >> Long ago I noticed that when using 807 transmitting tubes (!!!) (2 tubes >> good >> for 150 Watt AFAIR) they produced a (nice) blue glow at certain points on >> the >> envelope. These corresponded to certain "windows" in the metal valve >> elements >> and it seemed highly likely that accelerated electrons were striking the >> glass and producing the glow.* > > That is glass fluorescence. It is not caused by ionising radiation. > >> The magnitude of the glow varied with RF output and seemed to be maximum >> at >> maximum RF output in any given situation. This was slightly away from the >> plate dip point which was the usual way to tune a final stage. Others in >> the >> school radio club ridiculed this method but I subsequently found them >> using >> it. I don't recall ever hearing about this being used or reported by >> anyone >> else but it must have been common enough knowledge. > > Other tubes that did this were PL506/509 EL34 EL36 and similar beam > tetrodes and pentodes, as well as DY87/807 etc kenotrons. Any glass tube > will do this with enough anode volts. > >> At the time I wondered about the nature of the glow and whether it was >> accompanied by a degree of irradiation with harder invisible 'stuff'. >> Odds >> are it was :-). I'm not at all sure what the electron velocity is in a >> transmitting tube, but Cherenkov radiation seems a plausible explanation >> for >> the effect. > > The 807(B) was a much liked tube for ham radio. PL506/509 was H output > in B/W valved TVs. DY87/807 was the HV rectifier in same. EL34 and 36 > were used in audio amplifiers (100V line and such, running 600V plate > voltage). > > There are actually two kinds of visible effects in a hard driven tube, > electric blue light that seems to appear in the tube and is likely > caused by residual ions, and pale green fluorescence in the glass > proper. The latter may mean you have X rays ;-) > > Peter > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist