[Amps] SB-220 update and gettering

[Lee]

John,

OK I understand what you are saying.  But, how does a graphite 3-500Z 
tube get gettered after sitting around?  You say heating the anode to 
glow does not getter the tube.  I realize the graphite tube was gettered 
when manufactured.  Since glass seals leak, can a graphite 3-500Z be 
gettered again down the road or was it a one time deal at the factory?

Lee, w0vt


On 11/26/2016 5:37 PM, John Lyles wrote:
> 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