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ham_radio:varian_cpi_twt_model_numbers [2013/01/08 19:00] (current)
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 +====== Understanding Varian/CPI Model Numbers ======
 +From the MW Mailing List:
 +>   So I am trying to decide what tube to try first for the 10 
 +> GHz side Once long ago I saw/had an old Varian DOS program to 
 +> knew tube numb brrrs. Ideally there must be some good spec 
 +> sheets and or design notes for these tubes at their intended ​
 +> bands, anybody, something? ​ Most Google stuff seems to be as 
 +> much folk culture as fact, or limited in depth.
 +>   What practical experience is there out in MW world moving ​
 +> this family of tubes around?
 +>   ​Thanks in advance and HNY   Ted WA8ULG
 +The third letter refers to the radar band:
 +VTC = C band: nominally 4-8 for radar and ECM, or 5.85-6.45 for Satcom,
 +typically WR-187 waveguide output
 +VTX = X band: nominally 8-12 for radar and ECM, or 7.9 to 8.4 for Satcom,
 +typically WR-112 waveguide output for Satcom, and WR-90 for radar/ECM
 +VTU = Ku band: nominally 12-18 GHz for radar and ECM, or 14.0 to 14.5 for
 +Satcom, either WR-75 or WR-62 waveguide output.
 +At lower power (100W or less in C and X, 50W or less in Ku band), all bands
 +may have coax outputs.
 +The first 4 numbers refer to the vacuum envelop, and mean nothing other than
 +tubes that have the same 4 numbers started as basically the same tube. The
 +last 2 characters (H1, C4 and whatnot) are just variants, sometimes not more
 +than just a particular customer specification that requires a particular
 +adjustment or measurement,​ sometimes more profound differences,​ such as
 +orientation of the waveguide output.
 +Helix TWTs are fairly broadband in general, so an X or Ku band tube should
 +be usable at 10.368, maybe less likely for a Ku band tube, particularly if
 +it's high power (high power tubes 200W and higher tend to be more highly
 +optimized for their intended band of operation) or if it has WR-62 output
 +waveguide (12-18 GHz). If the tube has a WR-75 output (10-15 GHz), you are
 +much more likely to be able to use it at 10.368.
 +A lot of the lower power tubes (50W and less) are close derivative of broad
 +band jamming tubes, and are more likely to be usable outside their original
 +One possible issue is the output window, which may have bad resonances
 +outside it's intended bandwidth and may blow up at high power. That may be
 +hard to detect without a network analyzer. Do a fine gain analysis at low
 +power and look for sharp resonances near your operating frequency. If you
 +have sharp variations, beware. Another issue, more easily dealt with is
 +focussing. Pay attention to the helix current as you increase the power.
 +Most tubes will be damaged with as little as 10 mA, sometimes less. It
 +depends where the current goes. If it's spread over several turns of the
 +helix, you will be OK, but if it falls on a single turn, the tube will die
 +quickly. The problem is that there is no way to know where the current goes,
 +so it's best to be careful if it goes up. If helix current goes up sharply
 +well before you reach the rated power, you may be able to improve (reduce
 +it) by adjusting the helix or collector voltage. More adventurous types may
 +attempt to refocus the tube. That's not for the faint or heart!
 +We have used a lot of Varian/CPI tubes where I work, and we have a lot of
 +older specs. You may want to check their web site also
 +http://​www.cpii.com/​product.cfm/​1/​19 ​
 +Keep in mind that the most significant part of the model number is the 3
 +letters and first 4 numbers, and you may find equivalent tubes in the
 +catalog today.
 +Didier KO4BB
ham_radio/varian_cpi_twt_model_numbers.txt ยท Last modified: 2013/01/08 19:00 (external edit)
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