|[AMRadio] Screen Modulated 813|
collinsradio at adelphia.net
Mon Dec 11 14:09:12 EST 2006
Did you ever know that the 811A's in the Collins 30L-1 do show color under
modulation? If any one of the four tubes does not, then, that tube should
An 813 normally does not show color, unless the plate is the metal variety
and not the carbon plate. I would agree that this tube should operate
without any blushing whatsoever.
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----- Original Message -----
From: "Gary Schafer" <garyschafer at comcast.net>
To: "'Discussion of AM Radio in the Amateur Service'"
<amradio at mailman.qth.net>
Sent: Monday, December 11, 2006 1:34 PM
Subject: RE: [AMRadio] Screen Modulated 813
> The 813 and 572 are tubes that should never show color.
> Gary K4FMX
>> -----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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