The 813 and 572 are tubes that should never show color. 73 Gary K4FMX
> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:amradio- > [EMAIL PROTECTED] On Behalf Of Jim Wilhite > Sent: Monday, December 11, 2006 12:24 PM > To: Discussion of AM Radio in the Amateur Service > Subject: Re: [AMRadio] Screen Modulated 813 > > You are most correct John, I was speaking of power tubes not > the lesser cousins. I didn't make that clear but in light > of the subject, I plead not guilty. > > Jim > W5JO > ----- Original Message ----- > From: "John Lawson" <[EMAIL PROTECTED]> > To: "Discussion of AM Radio in the Amateur Service" > <amradio@mailman.qth.net> > Sent: Monday, December 11, 2006 10:35 AM > Subject: Re: [AMRadio] Screen Modulated 813 > > > > > > > > On Mon, 11 Dec 2006, Jim Wilhite wrote: > > > >> Yes, but we in the amateur service do not even consider > >> running them at the max. Red is ok if you take into > >> consideration all parameters and follow design > >> considerations. > > > > Dave Knepper also writes: > > > >>The reason that the tube is a bit cherry red is to > >>continually remove built-up gasses inside the tube. > > > > > > > > There is a wealth of practical, hands-on - and also > > theoretical, knowledge available on this List - a rarity > > among reflectors to be sure. Jim has provided myself and > > many others with constant 'good information' regarding AM > > transmitting gear. > > > > > > But.... but but but: Speaking as a design engineer, > > lifelong tube-geek, and (moderately succesful) thermionic > > designer - I would like to make the point that plate > > incandescance may, or may not, be 'OK'.... depends on the > > device amd the regime it's run in. > > > > > > Unless designed for such dissipation, it is most > > certainly NOT OK to run many tubes at a blush. The > > venerable 6146 is a case in point - running the plates red > > in a 6146 alters them irreversibly and generally kills > > 'em... get a 'fresh' one, test it for Gm, run it good and > > red for a while, then re-test. ooops.... > > > > There are of course tubes designed to run red, even > > bright yellow - like the various radiation-cooled tubes - > > IIRC 4-65s, etc... There are some tubes, like the 833, > > that can stand a little color and not get terribly upset. > > > > > > Running plates red does not, in most cases, re-adsorb > > gasses - if anything it facilitates thier release - > > depends entirely on the plate alloy, thickness, and any > > coating, element spacing, grid material and design, spacer > > materials, etc., etc.. You can't just make generic > > generalizations like this... the situation is way more > > complex. Red plates also has implications for permanent > > grid damage - not to mention that fact that we want that > > plate to collect electrons, not emit a bunch of them... ;} > > > > > > And as for "running them to the max" - all tubes have a > > point of maximum 'efficiency' where the power transfer > > function is optimal. Is the plate red at that place under > > the curves? If it's a radiation-cooled tube, you bet. If > > it's a 6146 - it just died. And just who is the "we" you > > speak of? ;} I run my Valiant on the raggedy edge most of > > the time - and I've chewed up one brand new set of finals > > finding out just where that edge is... d'oh! But now I > > know just how to get the max out of the transmitter and > > still keep the Output Devices happy - even if I do make > > 'em sweat good and hard... > > > > > > Anyway - the study of the theory and design of vacuum > > tubes is pretty damn fascinating to me - and if anyone is > > interested, I have a fairly comprehensive bibliography on > > the subject that I'd be happy to post, if there is any > > interest. And seeing as how most of us are using power > > tubes, and building / operating devices using power > > tubes - might save some bucks in the long run. > > > > > > Just my 200 millidollar for a Monday Morning... > > > > > > > > Cheers and Best of the Season > > > > > > John > > KB6SCO > > DM09fg > > > > ______________________________________________________________ > > AMRadio mailing list > > List Home: http://mailman.qth.net/mailman/listinfo/amradio > > Partner Website: http://www.amfone.net > > Help: http://mailman.qth.net/mmfaq.html > > Post: mailto:AMRadio@mailman.qth.net > > > > > > > ______________________________________________________________ > AMRadio mailing list > List Home: http://mailman.qth.net/mailman/listinfo/amradio > Partner Website: http://www.amfone.net > Help: http://mailman.qth.net/mmfaq.html > Post: mailto:AMRadio@mailman.qth.net ______________________________________________________________ AMRadio mailing list List Home: http://mailman.qth.net/mailman/listinfo/amradio Partner Website: http://www.amfone.net Help: http://mailman.qth.net/mmfaq.html Post: mailto:AMRadio@mailman.qth.net
