koØm
11-01-2010, 12:29 PM
In my 39 year experience of troubleshooting electrical and mechanical devices down to component level and repairing them, I have suddenly run into a spate of issues that have me stuck in neutral. Normally, when issues pop up, I just go get a cup of coffee or, leave it alone for a day or so and then get back to it with good results; not so this time.
To sum it up, suddenly while "Qualifying" a device for delivery, the equipment on my work bench seemed to systematically have developed problems:
1. A mono-band amplifier using two of the 813 type of tubes died while I was using it as a driver.
2. My Yaesu FT-101 E radio developed receiver problems; it went "deaf".
3. My Bird 43-P wattmeter went erratic and non-responsive.
4. I smoked one Radio Shack digital VOM because the input maximum was 400 ma, oops!
5. My Heath Cantenna/Non-radiating load changed in value.
I have spent more time fixing the test equipment so that I can demonstrate that this device works and to establish a price and warranty expectation than working on the item. My readings keep changing. The resistance on my Dummy Load is 50 ohms cold and, Zero ohms after 30 seconds at 600 watts; then after cooling some, the value goes up to 230 ohms and drifts down until it gets to 50 ohms. This sent me tearing into the Bird wattmeter before I realized the load was going crazy.
I observed this a number of times over a 2 day period (at first, I thought the replacement RS meter was gimp) because, Heath kit Canntennas cannot go bad, right? I have owned this Dummy Load for 30+ years and it still has the same oil in it from when I first filled it.
I spent the better part of 3 hours yesterday disassembling and re-assembling the 50 ohm Dummy Load; twice, once to inspect it and, the second time to replace the 50 ohm element, the SO-239, and to remove the meter circuit that is native to this device. The only thing that I did not change was, the Mineral Oil in the can.
Question: After 30 years of “Tube w/handles QRO” what would be the failure mode for the Heath Non-Radiating Load and, how are the properties of the Mineral Oil changed by 30 years of QRO Radio Frequency energy?
.
To sum it up, suddenly while "Qualifying" a device for delivery, the equipment on my work bench seemed to systematically have developed problems:
1. A mono-band amplifier using two of the 813 type of tubes died while I was using it as a driver.
2. My Yaesu FT-101 E radio developed receiver problems; it went "deaf".
3. My Bird 43-P wattmeter went erratic and non-responsive.
4. I smoked one Radio Shack digital VOM because the input maximum was 400 ma, oops!
5. My Heath Cantenna/Non-radiating load changed in value.
I have spent more time fixing the test equipment so that I can demonstrate that this device works and to establish a price and warranty expectation than working on the item. My readings keep changing. The resistance on my Dummy Load is 50 ohms cold and, Zero ohms after 30 seconds at 600 watts; then after cooling some, the value goes up to 230 ohms and drifts down until it gets to 50 ohms. This sent me tearing into the Bird wattmeter before I realized the load was going crazy.
I observed this a number of times over a 2 day period (at first, I thought the replacement RS meter was gimp) because, Heath kit Canntennas cannot go bad, right? I have owned this Dummy Load for 30+ years and it still has the same oil in it from when I first filled it.
I spent the better part of 3 hours yesterday disassembling and re-assembling the 50 ohm Dummy Load; twice, once to inspect it and, the second time to replace the 50 ohm element, the SO-239, and to remove the meter circuit that is native to this device. The only thing that I did not change was, the Mineral Oil in the can.
Question: After 30 years of “Tube w/handles QRO” what would be the failure mode for the Heath Non-Radiating Load and, how are the properties of the Mineral Oil changed by 30 years of QRO Radio Frequency energy?
.