Garey Barrell
Fri, 29 Aug 2008 14:24:14 -0700
Ron -No doubt that Sylvania was/is the best. Zenith branded tubes were ALL made by Sylvania as well, so they are fine. RCA tubes worked fine, and were often subbed in new production transmitters. The few times I used GE tubes in the 60's I found them to drop off about 10% from "new" output power levels in the first few hours of use, where the Sylvania tubes had a fairly smooth fall-off from new to worn out. I was using three T-4X/B transmitters in full power RTTY Autostart service then, and found that the Sylvania tubes would last about two years. Again, this was with full power output on 20M with transmissions often exceeding 30 minutes. There were small fans on each transmitter final cage of course. By the way, "worn out" was when the power output on 20M dropped to 100W.
I find it much easier to first neutralize on 20M, where the "sweet spot" is considerably broader and easier to find with new finals. Once in the ballpark on 20M it is only a slight refinement to effect neutralization on 10M. Certainly keeping the LOAD control at 0 as you say sharpens the neutralization "dip".
The International brand tubes were toward the end of tube manufacture, and were made by MANY different manufacturers, which is the reason they vary all over the map from "OK" to "dud". Raytheon is another brand that varies considerably along with Westinghouse. None of those companies actually "made" tubes, so you never knew what you would get, especially toward the "end".
The notice published by Drake was very late, in fact it referred to the inability to obtain production quantities of "Phillips/Sylvania" tubes which were the predecessor to "ECG/Sylvania". By this time "GE" branded tubes were also quite possibly NOT manufactured by GE. This sourcing problem was also the reason for the change from 6EV7 to 6FQ7 and even to the 6AQ8 in the Relay Control spot.
73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs <www.k4oah.com> Ron Baker wrote:
For what it's worth, I have found the Sylvania by far are the best but I have found no matter whether its a Sylvania, RCA, or GE, they all will neutralize in the transmitter as the circuit was designed by Drake. I have found when a tube would not properly neutralize the tube was either bad or weak or on the verge of going bad. Also if your looking for a dip on 10 meters first put the loading to "0", or to the far left. This will give you the maximum "dip" effect. Advancing the loading from that point the "dip" becomes more shallow and less apparent on the meter. Regarding the final tubes stay with the above mentioned brand tubes. I have found most of the other brands have a tendency to not do well especially on the higher bands. I found the "International" brand tubes to be the absolute worst possible final tube to use in Drake. I acquired several brand new International and ended up tossing all of them because everyone appeared somewhat different, and forget trying to find a match pair. 73, Ron / WB4HFN
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