Actually, sweep tubes used in TV service, back in the day, were beat upon fairly hard.
What you don't want to do, with ANY tube transmitter, is run heavy plate current OFF-RESONANCE.? When that is done, the dissipation ratings are probably being exceeded.? This can happen with 6JB6's but also with 6146's, 811's and 3-500Z's.? It is important to get the PLATE tuning at least into the "ballpark" when tuning.? You can do this with low plate current, then increase drive and fine-tune the loading and the RF TUNE adjustments.
I don't know where the perception that sweep tubes are delicate came from.? They're really not any more delicate than the famous 6146.
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
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On Wednesday, April 2nd, 2025 at 5:27 PM, amfone via groups.io <amfone20000@...> wrote:
You should always tune up FAST for the Drake gear, these are sweep tubes. One way to check the quality of the tube is to set the bias to the proper point and transmit for about 3 minutes or more using SSB and if you see the Bias rise you have a weak tube or tubes.
73 Tim
WB8UHZ
On Wednesday, April 2, 2025 at 11:33:51 AM EDT, John Magliacane via groups.io <kd2bd@...> wrote:
On Wednesday, April 2, 2025 at 10:28:21 AM EDT, Craig W8CS via groups.io <craig_severson@...> wrote:
> How do you determine that your final tubes are near EOL?
Craig,
The "sagging" plate current or RF output effects you saw are evidence of a soft tube somewhere in the transmitter chain.
If you have a tube tester, you can try lowering the filament voltage a volt or two and observing what the tester reports in terms of Merit or Transconductance. A tube that is reaching EOL will produce an obvious drop in in tube tester response when the filament voltage is lowered. A good tube with a lot of "life" remaining will remain fairly steady, even with slightly lower filament voltage.
73 de John, KD2BD
