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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 | ||
| + | |||
| + | Ted, | ||
| + | |||
| + | 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 | ||
| + | band. | ||
| + | |||
| + | 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 | ||