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70327How much abuse can an RXTX take?

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  • warrenallgyer
    Nov 22, 2012
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      Secure in the knowledge I had a drawer full of replacements I decided to ask a pair of BS170 finals to take one for the team. I decided to do key-down, destructive testing to see how long they could run at full drive, full output before failing.

      My RXTX 30/20/17 puts out a whopping 3.3 watts at 13.8 VDC and full drive. I have always been very careful at this power level and backed it off considerably in actual operation. For this test I decided to run it at that power until it failed. I set up a spread sheet to log the total current drawn and the power output at 30 second intervals until the inevitable smoke began escaping front he KM5H case.

      At key down the rig produced 3.3 watts and total current drawn was 595 ma. After 2 minutes the power was down to 3.0 watts and current at 560 ma. At 8 minutes it was down to 2.8 watts out and 545 ma.

      So how long did the finals last. Well, after a full hour of key down they were still making 2.7 watts and drawing 525 ma. At that point I pardoned them with a hearty "well done!" and terminated the test.

      The KM5H case became noticeably warm at about 15 minutes. By 30 minutes it was very warm but it did not heat up more after that. I did not take the cover off at any point because I wanted to simulate real operating conditions so I don't know about the heat distribution inside.

      Bottom line, even at nearly 3 watts for a full hour the rig was making stable and very high power. No thermal runaway, no failure of any kind. Another tribute to a very solid, rugged design.

      Warren Allgyer - W8TOD
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