[AMRadio] Screen Modulated 813


Gary Schafer garyschafer at comcast.net
Mon Dec 11 14:51:16 EST 2006


The 811A should "show a barely perceptible red color at maximum dissipation"
(per the RCA tube manual).

The 30L-1 pushes the tubes a little beyond their limits. Add a little speech
processing and they get pushed even harder.

73
Gary  K4FMX

> -----Original Message-----
> From: david knepper [mailto:collinsradio at adelphia.net]
> Sent: Monday, December 11, 2006 2:09 PM
> To: garyschafer at comcast.net; Discussion of AM Radio in the Amateur Service
> Subject: Re: [AMRadio] Screen Modulated 813
> 
> 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
> be replaced.
> 
> 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.
> 
> 
> Dave, W3ST
> Publisher of the Collins Journal
> Secretary to the Collins Radio Association
> www.collinsra.com - the CRA Website
> Now with PayPal
> CRA Nets: 3.805 Mhz every Monday at 8 PM EST
> and 14.253 Mhz every Saturday at 12 Noon EST
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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.
> >
> > 73
> > 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.
> >>
> >> Jim
> >> W5JO
> >> ----- 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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> >>
> >>
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