[Amps] SB-220 update and gettering

[John Lyles]

Hello Rob,
I believe that you misunderstand that I am only talking about graphite 
anode tubes. Sheet metal anodes with vertical fins, made with Tantalum, 
which is what Eimac and some knock-offs used, act as a getter 
themselves. The graphite anode 3-500Z originally was the Amperex/Covimag 
version. Covimag shut down as a factory just a few years ago. It appears 
that China is now copying or licensed to the same design with horizontal 
'fins' to improve radiation area.

I stand by my statement that graphite anodes do not act as a getter. 
They have a lot of other desirable properties, as discussed in the 1935 
paper I sent. Further discussions are found in chapters discussing anode 
materials in the RCA Tube Design bible from 1940 and the RCA Red Book 
electron tube bible (1962) which was originally only issued internally 
but is now found on the web photocopied. In addition, the text books by 
Kohl "Materials and Techniques for Electron Tubes" 1960 by General 
Telephone and Electronics discuss these aspects of tube manufacture. I 
understand that you do not have time to read these reference books and 
reports, but these describe the standard techniques that all tube 
manufacturers still follow, as no real breakthoughs have been discovered 
in the past 2 decades. The last big changes made in the 1990s are in the 
very high power tube arena, where pyrolytic graphite was developed for 
grids and multiphase liquid/vapor cooling was implemented.

There is nothing wrong with running graphite anodes with color, but 
vacuum improvement is not the result, only extra output from the device 
as well as the extra dissipation internally. There is some amazement at 
the antics that some hams will do to enhance their tubes by running 
periodic overheat to try and reduce vacuum pressure. With sheet metal 
anodes, it is very common to have orange or even red color in the center 
of the anode. With graphite, it is merely running them harder. Many 
tubes also have tab getters near the filament that are activated with 
filament heat, which leads to the specification on datasheets to warm up 
the tube for 15-30 minutes before first HV is applied.

As an amplifier designer professionally, since 1981, for broadcast FM, 
industrial RF generators, and particle accelerators, I am somewhat 
familiar with tube use and misuse. I will agree with you about the use 
of chimneys and lots of air, water, to properly remove the heat from a 
tube.

73
John
K5PRO

On 11/26/16 12:57 PM, Rob Atkinson wrote:
> You're sending me a long paper from 1935 30 years before the 3-500Z,
> which is the tube I am discussing, although I may have incorrectly
> described it as an internal anode graphite tube.  I don't have time to
> wade through a 4 or 5 page Ph.D. paper--I have a job and a lot of
> other work to do.  If you want to ignore decades of advice and
> experience with these tubes from every other authority out there and
> run them with them never showing any color go ahead.  I've seen I
> don't know how many broadcast rigs and linear/non-linear RF amplifiers
> with one or another member of the 3/4/5-125/250/400/500/1000 showing
> color as a normal part of their operation.  Sorry, I'll stick with
> what design engineers seem to know, with chimneys and a lot of air.
>
> 73
>
> Rob
> K5UJ