I just acquired three 3-500Z medical pulls from pulse service. I'm not
thrilled with my test results, but maybe my expectations are too high. The
tubes are guaranteed to be 100% output, but I'd say they're more like
90%-95%. I tested them one at a time in an LK550, on 20M with about 60W
drive. Then I tested them together on all bands in the 550. Here are the
test results, compared with the orginal tubes that were in the 550. The
three pulls have 1996 date codes. All three original tubes have date codes
about 20-years old. The original tube marked "NOS" is a recently purchased
new-old-stock tube with a 1978 date code.
Medical Pulls Original Tubes
Tube Ip Ig Output %full pwr Tube Ip Ig Output
#1 400mA 130mA 575W 96% #1 400mA 90mA 600W
#2 400 120 550 92 #2 440 100 600
#3 400 125 550 92 NOS 440 100 600
Pulls Together %full pwr Original Together
80M 800mA 350mA+ 1450W 97% 80M 840mA 270mA 1500W
40M 880 350+ 1500 91 40M 960 320 1650
20M 860 330 1425 95 20M 880 290 1500
15M 880 350 1400 89 15M 1000 300 1575
10M 1000 350+, 1300 87 10M 1120 310 1500
The "%full power" figure is just the output from the pulls divided by the
output from the original tubes. One thing that really stands out is the
difference in grid current. Is that something that happens to tubes as they
start winding down, or is that normal? Do later 3-500Zs pull more grid
current than old ones? I might have been able to push the pulls a little
harder on the higher bands, but the grid meter was pegging and I didn't want
to damage them.
I'm inclined to send the tubes back. Opinions?
BTW, the pulls were purchased to free up two of the original tubes, which
are on loan from an SB-221.
73, Dick WC1M
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