Tuesday, March 11, 2008

New Tubes

I have installed a "Matched Pair" of RF Parts Inc. Taylor 572B tubes in my Heathkit SB-200. As it turned out, one of the original Centron tubes was not performing well - it also had somewhat lower idle current. Those new tubes are probably made in China and just branded under the "Taylor" brand. After installing the new tubes, I left the amp turned ON with no drive for about 4 and a half hours. This serves to condition the tubes and to minimize the chance for flash-over and in general it is a good practice with new tubes and tubes with unknown shelf life. The heat from the filament activates the "getter" which is deposited on the plate. The "getter" is a chemical composition which reacts with any free (gas, metal) molecules in the tube and improves the vacuum.
The tubes are working fine and I am getting over 850W on 80 meters when tuning with pulser. On 40,20 and 15 meters the output is a bit lower - 750+ Watts which is still pretty good for this amp! When I heated the plates with continuous drive, I noticed that one of tubes got a little bit hotter than the other (judging by the plate color). I am planing to buy another pair for spare and will try to re-match them. It is also a good practice to "rotate" the tubes in the amp with the spare ones every year or so and not allow any of the tubes to spend too much time on the shelf. Vacuum tubes don't age well when they are not in use.

The new RF Parts Inc. "Taylor" tubes to replace old Centron tubes. The tubes are from the same factory batch and have writings on the glass envelope with the test results from the "matching" procedure. I cleaned them with alcohol to prevent "hot spots" from forming due to fingerprints. As a side effect the alcohol wiped clean all of the markings along with the red Taylor logo.

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