[AMRadio] Screen Modulated 813

david knepper collinsradio at adelphia.net
Mon Dec 11 14:05:47 EST 2006

Exactly, John.  If a transmitting tube is operating within manufacturer's 
specifications and does not show color then don't increase the plate current 
or voltage to do so.

Many transmitting tubes are meant to show some blushing, particularly, 
modulators - this is normal and acceptable.

You wouldn't, of course want to this occur with a 6146, etc.

My point was that many hams mistakenly think that with some tubes like those 
that I mention there should be no blushing - quite the contrary.  Blushing 
is good for tubes and, of course, for women, under certain circumstances!

Merry Christmas

Dave, W3ST
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com - the CRA Website
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----- 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 12:50 PM
Subject: Re: [AMRadio] Screen Modulated 813

> On Mon, 11 Dec 2006, david knepper wrote:
>> Zirconium getters best at about 1000 degrees C, this why large metal 
>> anode transmitting tubes like the 4-400A, 4-1000A, and 3-500 must be 
>> operated with a dull red to red anode color.  Zirconium also releases 
>> some gasses and
>   [snip]
>> You can do what you will but I like to run a little color on my large 
>> bottles.
>   You're making the same point I am, Dave: "visible plate incandescance" 
> can be 'optimum' - 'acceptable' - 'acceptable for x-time' - 'not 
> recommended - or 'disastrous'. It's device-dependent!
>   All of it is a matter of physics, physical electronics, metallurgy, and 
> the well-known, well-documented aspects of thermionic device design and 
> contruction. It is not so much a matter of desire or personal inclination, 
> as it is: at the operating point you have set for the particular device in 
> use - is it within the manufacturer's ratings for that service?  If the 
> plate shows visible color, so be it. If, on the other hand, a noticeable 
> blush means the tube is exceeding it's design-spec, then some consequences 
> will come from that... "good" or "bad" I cannot say.  If an expensive 
> power tube has it's useful life cut in half, or more, from 'abuse' - 
> especially if it's a fairly 'rare' type - well then....
>   Dat wuz all I wuz tryin' t' say.
>    Cheers  and Best of the Season!
> John
> DM09fg
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