[Boatanchors] Suppressor grid modulation

[Carl]

The confusion with the 813 lies partly with RCA inasmuch that they insisted 
on showing the beam forming plates as a true grid in both the full 
engineering spec sheet and in TT-4. The only mention of that element is to 
run 0 volts (with a subscript mentioned later) and the diagram clearly 
designates it as G3/IS. To their credit the heading is called "Beam Power 
Tube".

It is also one of the very few beam tubes that had the beam plates 
terminated in a seperate pin.

Also overlooked by many builders is the little subscript paragraph stating 
that G3 should be returned to the filament transformer CT on AC or the 
negative end of the filament on DC. Some simply ground it to a convenient 
point resulting in possible instability.

IMO the 813 is highly underated and is capable of much higher voltage and 
dissapation than listed. Comparing just the anode mass to a 572B which is 
smaller indicates that the 100W Pd rating is off by a factor or 2 or so. Ive 
been running them on AM for a few years with 2900V and they barely show the 
slightest trace of color on 125% positive voice peaks and no trace of lost 
emission. Others have run them up to 3500V.

Carl
KM1H



----- Original Message ----- 
From: "mac" <w7qho at aol.com>
To: "Paul Baldock" <pbaldock at verizon.net>; "Boat Anchors List" 
<boatanchors at mailman.qth.net>
Sent: Wednesday, January 27, 2010 10:41 PM
Subject: Re: [Boatanchors] Suppressor grid modulation


> The confusion with the 813 likely stems from the fact that the
> standard base diagram (5BA) called out for this tube in the ARRL
> Handbooks (since 1946), Fathour, Sibley, and other references seems to
> show a suppressor grid connected to Pin 5.   ARRL Handbooks 1941
> through 1945 mistakenly show the 813 as some kind of a dual triode and
> prior to this do not list 813 specs at all.  At least in my library,
> only my 1948 Radio Handbook shows a base diagram with beam forming
> plates.
>
> Dennis D. W7QHO
> Glendale, CA
>
>
>
>
>
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