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How do you determine that your final tubes are near EOL??
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Currently when I tune up my T-4XC, particularly when I peak the "Load" control I have to perform this really quickly to get a peak, because iP and output power will slowly fall if I hold this for more than a couple of seconds. I have to "chase" the load peak with a falling ammeter.?
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I don't know if what I'm seeing is related more to a secondary effect, such as the cathode resistors heating up and increasing their resistance, or whether the finals themselves are getting "soft."?
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I can still achieve >100W output on all bands. The AC-4 has been recently rebuilt. I'm sure that I can determine the root cause with time, but I'm curious how y'all determine the health of your final tubes.?
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Craig/W8CS
Greenville, SC
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Chances are that it¡¯s only one tube. I have a TR-4Cw RIT that¡¯s doing the same thing and I¡¯m going to need to swap one tube at a time until the problem stops. Keep in mind that it could also be a driver ¡ª try swapping that first.?
Always return a functioning tube back into its place if it turns out to not be the culprit.?
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Wed, Apr 2, 2025 at 10:28, Craig W8CS via groups.io < craig_severson@...> wrote:
How do you determine that your final tubes are near EOL??
?
Currently when I tune up my T-4XC, particularly when I peak the "Load" control I have to perform this really quickly to get a peak, because iP and output power will slowly fall if I hold this for more than a couple of seconds. I have to "chase" the load peak with a falling ammeter.?
?
I don't know if what I'm seeing is related more to a secondary effect, such as the cathode resistors heating up and increasing their resistance, or whether the finals themselves are getting "soft."?
?
I can still achieve >100W output on all bands. The AC-4 has been recently rebuilt. I'm sure that I can determine the root cause with time, but I'm curious how y'all determine the health of your final tubes.?
--
Craig/W8CS
Greenville, SC
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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
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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
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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.
Sent with secure email.
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
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Probably because sweeps are pulse tubes and are not built to take high levels of average power. The 6146 and such were more robustly built and would typically be used in FM or AM service. On Thu, 03 Apr 2025 00:06:42 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: 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 -Jim NU0C
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Back in the day, I built a linear with 4 6LQ6 tubes ( in an ARC-5 cabinet ).
I used Radio Shack "lifetime warranty" tubes, and carefully put the receipt in
an envelope taped to the bottom of the linear.
- Jerry, KF6VB
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On 2025-04-02 17:47, Jim Shorney via groups.io wrote: Probably because sweeps are pulse tubes and are not built to take high
levels of average power. The 6146 and such were more robustly built
and would typically be used in FM or AM service.
On Thu, 03 Apr 2025 00:06:42 +0000
"Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote:
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
-Jim
NU0C
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Hello all,
¡®Somewhere¡¯, years ago, I read ¡®something¡¯ about the typical sweep tubes, stating they were being used WAY beyond their ratings.
It was because of SSB duty cycle of ~18% that they were even used at all.
This is only what my ¡®old mind¡¯ remembers.
The 6146 has got to have better numbers.
Maybe they should have used 4D32¡¯s like the Collins 32V2 used (hard to kill those WWII radar tubes).
73 de Steve NR4M
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On Apr 2, 2025, at 8:06?PM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
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.
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Here¡¯s how I ¡°Identify¡± soft tubes:
?
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73, Ron
AF5IV
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I stand corrected. The difference between a tech (me) and a trained engineer.?
Having said that, the sweep tubes will stand up to a lot of use, as long as they aren¡¯t abused.?
Having also worked on a few Kenwood hybrids, I¡¯ve seen more toasted 6146¡¯s in the last few years than 6JB6¡¯s and the KW rigs weren¡¯t used on 11m.?
If you do your initial plate-tuning at 150mA or so, you¡¯ll get lots of life out of the finals.?
When I get around to looking at my TR-4Cw RIT, I¡¯ll report back on my findings. This set had somewhat soft PA tubes to begin with, so I replaced them with used tubes from my stock. These stock tubes were all tested in my Hickok tester, so it bears repeating that tube testers only tell you what is definitely bad and possibly good :-)
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Wed, Apr 2, 2025 at 23:18, Steve Bookout, NR4M < steve@...> wrote: Hello all,
¡®Somewhere¡¯, years ago, I read ¡®something¡¯ about the typical sweep tubes, stating they were being used WAY beyond their ratings.
It was because of SSB duty cycle of ~18% that they were even used at all.
This is only what my ¡®old mind¡¯ remembers.
The 6146 has got to have better numbers.
Maybe they should have used 4D32¡¯s like the Collins 32V2 used (hard to kill those WWII radar tubes).
73 de Steve NR4M
> On Apr 2, 2025, at 8:06?PM, Steve Wedge, W1ES/4 via groups.io <w1es@...> wrote:
>
> 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.
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Assume that the design engineers were fully aware of the operation limits of the 6JB6 tubes the expected lifetime should be long.? Keep in mind that these tubes were developed as the horizontal amp in TV sets.? These operated at the same conditions all of the time.? At that use they cost me 67 cents each. ? So assuming? that this results in a? shortened lifetime? it is likely a result of likely operator abuse.
David Assaf III
W5XU??? VP8RXU
I stand corrected. The difference between a tech (me) and a trained engineer.?
Having said that, the sweep tubes will stand up to a lot of use, as long as they aren¡¯t abused.?
Having also worked on a few Kenwood hybrids, I¡¯ve seen more toasted 6146¡¯s in the last few years than 6JB6¡¯s and the KW rigs weren¡¯t used on 11m.?
If you do your initial plate-tuning at 150mA or so, you¡¯ll get lots of life out of the finals.?
When I get around to looking at my TR-4Cw RIT, I¡¯ll report back on my findings. This set had somewhat soft PA tubes to begin with, so I replaced them with used tubes from my stock. These stock tubes were all tested in my Hickok tester, so it bears repeating that tube testers only tell you what is definitely bad and possibly good :-)
Steve Wedge, W1ES
Time flies like an arrow. Fruit flies like a banana.
On Wed, Apr 2, 2025 at 23:18, Steve Bookout, NR4M < steve@...> wrote: Hello all,
¡®Somewhere¡¯, years ago, I read ¡®something¡¯ about the typical sweep tubes, stating they were being used WAY beyond their ratings.
It was because of SSB duty cycle of ~18% that they were even used at all.
This is only what my ¡®old mind¡¯ remembers.
The 6146 has got to have better numbers.
Maybe they should have used 4D32¡¯s like the Collins 32V2 used (hard to kill those WWII radar tubes).
73 de Steve NR4M
> On Apr 2, 2025, at 8:06?PM, Steve Wedge, W1ES/4 via <w1es=[email protected]> wrote:
>
> 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.
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I think something else needs to be considered when there is discussion about how long the 6/12JB6 tubes will last is our present times.? When a lot of the folks that are regular contributors to this group got started with ham radio we had tube type PAs that required dipping and loading.? We learned how to use reduced drive to get to the initial dip and then bring up the power and stay in resonance.?? Now days there are lots of people that have had most of their experience with solid state equipment that does not require PA loading and if they have a poor antenna match or worse they usually have protection from a foldback circuit.
Having? groups like this hopefully will make the newer operators of these older pieces of equipment aware sooner rather than later about the proper "care and feeding" of these fine pieces of vintage equipment.
73, Ron? wa7gfe
?
I stand corrected. The difference between a tech (me) and a trained engineer.?
Having said that, the sweep tubes will stand up to a lot of use, as long as they aren¡¯t abused.?
Having
also worked on a few Kenwood hybrids, I¡¯ve seen more toasted 6146¡¯s in
the last few years than 6JB6¡¯s and the KW rigs weren¡¯t used on 11m.?
If you do your initial plate-tuning at 150mA or so, you¡¯ll get lots of life out of the finals.?
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Craig W8CS
Jim Shorney
David
Ron Magnus