[MyHosting.com]   [KO4BB Home Page]   [Manuals Home Page]   [KO4BB Wiki]

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 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

ham_radio/varian_cpi_twt_model_numbers.txt · Last modified: 2013/01/08 19:00 (external edit)
Recent changes RSS feed Creative Commons License Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki
Except as noted, this entire site Copyright © 2002-2017. KO4BB All rights reserved.