|[AMRadio] Screen Modulated 813|
garyschafer at comcast.net
Mon Dec 11 13:34:56 EST 2006
The 813 and 572 are tubes that should never show color.
> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] 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.
> ----- Original Message -----
> From: "John Lawson" <jpl15 at panix.com>
> To: "Discussion of AM Radio in the Amateur Service"
> <amradio at 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
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