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Author Topic: AL-811H with 572B tubes quick question  (Read 32358 times)
W8JX
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« Reply #60 on: September 04, 2016, 06:47:11 AM »

Of course, getting 1500 watts output 100% solid state is challenging.

Only real challenge is cost as it is quite doable but expensive to do correctly. Not only is it the price of the PA devices but the size or mass of heat sink needed to keep devices below temperature limits in any scenario which adds size, weight and cost. Liquid cooling would work better but would add to cost and complexity. SS amps are typically 40 to 50% efficient at best so for 1500 watts out you are looking 1500 to 1800 watts of heat to loose just from PA's (even more with a little SWR) and keep them cool (below temp limits) doing it. Most SS amps lack proper cooling for this and depend on thermal shut down when they get too warm because they lack proper cooling. Unlike tubes, PA transistor also have a max temp and very little room, if any, for error on the temp. This is why many SS amps fail over time.  
« Last Edit: September 05, 2016, 03:30:26 AM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
K6EB
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« Reply #61 on: September 01, 2017, 01:23:00 PM »

I own and run three Kenwood Hybrid radios that put out the usual 100+ watts when tuned properly.  I drive each of them into an Al-811H with 811A tubes.  I put out 800+ watts and I use only the SSB mode.  I get great audio reports with no distortion or splatter.  I keep threatening to switch to the 572B's, but the 811A's just keep churning away.  Been over a year now.  I guess I'm posting this because if you are using only SSB, the 85 watt maximum input might not apply.  I will probably switch to 572B's when/if the 811A's give out.  What do you think?
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W1QJ
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« Reply #62 on: September 02, 2017, 03:47:02 AM »

I own and run three Kenwood Hybrid radios that put out the usual 100+ watts when tuned properly.  I drive each of them into an Al-811H with 811A tubes.  I put out 800+ watts and I use only the SSB mode.  I get great audio reports with no distortion or splatter.  I keep threatening to switch to the 572B's, but the 811A's just keep churning away.  Been over a year now.  I guess I'm posting this because if you are using only SSB, the 85 watt maximum input might not apply.  I will probably switch to 572B's when/if the 811A's give out.  What do you think?

I think that is great.  You are obviously doing something right. After all the amp is rated for 800 watts pep on SSB.
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KM1H
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« Reply #63 on: September 03, 2017, 05:26:08 PM »

Quote
I think that is great.  You are obviously doing something right. After all the amp is rated for 800 watts pep on SSB.

But not with those tubes unless it is tuned up seldom and then real quick.

Even RCA's run at the 1000W FCC INPUT limit and figure on 600-650W out for 4 of them in the 30L1 could be damaged during tuneups.
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WY7CHY
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« Reply #64 on: September 05, 2017, 09:39:00 AM »

If you use a pecker to tune the amp with, you'll never have an issue with over driving in SSB mode. That's what I use. It makes tuning much easier and faster. Just leave the transmitter at it's normal output power in SSB mode, turn the pecker on, key into the amp and tune it up. You don't have to go through the low power in am/fm/rtty mode and gradually increase. Plus, because you're in SSB mode, the tuning is more accurate.

On a side note; I've used 811a tubes in my AL-811H. I've also used Ryazan g-811 tubes (Which I think are better). I also am currently using 572b tubes. The 572b tubes obviously can handle much more power, so there's no chance of hurting them. But in the end, even with the 572b tubes, I don't go past the 85 watts input. Not because of the amp, but because I don't run ANYTHING at 100%. My car can do 150mph, but I don't drive it 100%. It's harder on the car. An audio amp/stereo than can put out 200 watts isn't made so you WILL DRIVE 200 watts. It's made that high, so when you drive it at normal levels, the percentage of output is much lower and therefor the THD and similar is reduced. Granted, the cycle rate of SSB is much less than CW/AM/FM/RTTY, but there's no reason to crank out the full 100 watts. By reducing it to about 85 watts, the transceiver will transmit cleaner and cooler, and THUS, the amp will transmit cleaner and cooler.

And to top it off...... an increase in 1-S unit is a 6db gain. Meaning, you doubled your power twice. E.g. 100 watt transmitter amped up to 400 watts, is a 6db gain. Thus, 1-S unit gain on the receiving end. To go from 400 watts to 800 watts is another 3db gain. 1/2 of an S-Unit. If you take your AL-811H amp to 650-700 watts with 80-85 watts in, you'll only be about 1db less than if you pushed the full 800 watts. That 1db isn't even noticeable. So why not run BOTH the transmitter AND the AL-811H amp cooler, by only feeding it with 80-85 watts and putting out 650-700 watts? It's better for everything all around. Including the 811a tubes.

Just my $0.0309509303. (Inflation)
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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« Reply #65 on: September 06, 2017, 12:11:16 PM »

If you use a pecker to tune the amp with, you'll never have an issue with over driving in SSB mode. That's what I use. It makes tuning much easier and faster. Just leave the transmitter at it's normal output power in SSB mode, turn the pecker on, key into the amp and tune it up. You don't have to go through the low power in am/fm/rtty mode and gradually increase. Plus, because you're in SSB mode, the tuning is more accurate.

On a side note; I've used 811a tubes in my AL-811H. I've also used Ryazan g-811 tubes (Which I think are better). I also am currently using 572b tubes. The 572b tubes obviously can handle much more power, so there's no chance of hurting them. But in the end, even with the 572b tubes, I don't go past the 85 watts input. Not because of the amp, but because I don't run ANYTHING at 100%. My car can do 150mph, but I don't drive it 100%. It's harder on the car. An audio amp/stereo than can put out 200 watts isn't made so you WILL DRIVE 200 watts. It's made that high, so when you drive it at normal levels, the percentage of output is much lower and therefor the THD and similar is reduced. Granted, the cycle rate of SSB is much less than CW/AM/FM/RTTY, but there's no reason to crank out the full 100 watts. By reducing it to about 85 watts, the transceiver will transmit cleaner and cooler, and THUS, the amp will transmit cleaner and cooler.

And to top it off...... an increase in 1-S unit is a 6db gain. Meaning, you doubled your power twice. E.g. 100 watt transmitter amped up to 400 watts, is a 6db gain. Thus, 1-S unit gain on the receiving end. To go from 400 watts to 800 watts is another 3db gain. 1/2 of an S-Unit. If you take your AL-811H amp to 650-700 watts with 80-85 watts in, you'll only be about 1db less than if you pushed the full 800 watts. That 1db isn't even noticeable. So why not run BOTH the transmitter AND the AL-811H amp cooler, by only feeding it with 80-85 watts and putting out 650-700 watts? It's better for everything all around. Including the 811a tubes.

Just my $0.0309509303. (Inflation)

4 ea 572's is a waste of tubes in a AL811H amp. You will run out of power supply before you can really hurt even 3 of them and 4 will make not more power in that amp that 3 safely can.  Just three 572's have about 250% more safe dissipation that four 811a tubes....
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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« Reply #66 on: September 06, 2017, 12:21:40 PM »

I've experimented with 3 vs 4 tubes in the 811H. Unless there's a special combination of WHICH ONE to leave empty, I got more power out with 4 than with 3.

I understand mathematically, that because of what the tubes can handle, 3 is all you need. But in my 811H, I was only able to get about 600 watts out with 3 572b tubes. It took 4 to get the full rated output.

Again; maybe there's a pattern or a particular tube/slot that is to be left empty.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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Posts: 13268




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« Reply #67 on: September 06, 2017, 02:29:33 PM »

I've experimented with 3 vs 4 tubes in the 811H. Unless there's a special combination of WHICH ONE to leave empty, I got more power out with 4 than with 3.

I understand mathematically, that because of what the tubes can handle, 3 is all you need. But in my 811H, I was only able to get about 600 watts out with 3 572b tubes. It took 4 to get the full rated output.

Again; maybe there's a pattern or a particular tube/slot that is to be left empty.

You can safely load 3 ea 572's with more plate current than 4 ea 811's. Four 811's max out at 175ma per tube  which is 700 ma max. Three 572's can safely handle 825 ma.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KF7CG
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« Reply #68 on: September 06, 2017, 03:54:25 PM »

The power difference between 3 and 4 572b's is most likely due to reduced input and output impedances and a better match to both the input and output matching networks. This is just quick rough figuring. If 4 tubes yields a 50 ohm input impedance, then 3 might well be around 66 ohms. The output impedance of the tube group would also be some where near 4/3 of the impedance presented by 4 tubes.

It is not a certainty but this might account for at least some of the power reduction.

David
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W8JX
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« Reply #69 on: September 06, 2017, 04:17:25 PM »

The power difference between 3 and 4 572b's is most likely due to reduced input and output impedances and a better match to both the input and output matching networks. This is just quick rough figuring. If 4 tubes yields a 50 ohm input impedance, then 3 might well be around 66 ohms. The output impedance of the tube group would also be some where near 4/3 of the impedance presented by 4 tubes.

It is not a certainty but this might account for at least some of the power reduction.

David

I suspect it is from not properly loading and driving them. A 572 can SAFELY handle 55% more plate current than a 811.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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« Reply #70 on: September 07, 2017, 06:38:49 AM »

The power difference between 3 and 4 572b's is most likely due to reduced input and output impedances and a better match to both the input and output matching networks. This is just quick rough figuring. If 4 tubes yields a 50 ohm input impedance, then 3 might well be around 66 ohms. The output impedance of the tube group would also be some where near 4/3 of the impedance presented by 4 tubes.

It is not a certainty but this might account for at least some of the power reduction.

David

I suspect it is from not properly loading and driving them. A 572 can SAFELY handle 55% more plate current than a 811.

Well, I simply tune the amp like I normally would. Adjusting plate and load for max power out. Of course, I didn't exceed plate or grid current per the tuning instructions. And you're probably saying that with the 572b tubes, you CAN EXCEED the plate and grid current being they were written for the 811A tubes. That's possible.

With winter coming up, I'll probably experiment some more with the 3 vs 4 tubes. I am finishing up a repair on one of my other amps; FL-2100B; so I'll need to put the 572b tubes back in it. I'll go back to using my Ryazan G-811 tubes.

Honestly, if you already have 4 each 572b tubes; or you're able to get a set of 4 cheap, there's no "Waste" using 4 in the 811H amp. "WASTE" is a relative term. It's only a waste if you needed the money you spent on the 4th tube for something else. There's a lot of people who have a 500w, 800w, 1000w, etc. amp; and they only run it at 50-60% of it's rated capacity. That TOO is a WASTE; under certain people's definition. If you're going to only run 500w out of a 800-1000w amp; why not just buy a 500w amp?

The good thing about using 572b tubes in the 811H is that because the power supply will NEVER over drive the tubes, buying 1 set of 572b tubes will most likely be the LAST TUBES YOU EVER BUY for the 811H amp. Plus, you'll almost never be able to screw the tubes up during the tuning process. So, buying 4 each 572b tubes for the 811H isn't really a waste either, when you consider if you use the amp a lot, you'll never have to buy a replacement tube like you would with an 811A or G-811 tube. The cost of the 572b tubes is almost to the dollar TWICE the cost of the 811a tube. I.e. a set of 4 572b tubes can be bought for $220-$250. A set of 4 811A tubes (Same manufacturer) is about $120. Of course, if you're familiar with the G-811, you can get a set of 4 NOS for about $90-$100. POINT IS: Buying 1 set of REPLACEMENT 811A TUBES, would have been the SAME COST as buying just 1 SET of 572b tubes, which will be almost IMPOSSIBLE to burn out in an AL-811H amp.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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« Reply #71 on: September 07, 2017, 06:56:00 AM »


Well, I simply tune the amp like I normally would. Adjusting plate and load for max power out. Of course, I didn't exceed plate or grid current per the tuning instructions. And you're probably saying that with the 572b tubes, you CAN EXCEED the plate and grid current being they were written for the 811A tubes. That's possible.


It is pretty silly to run a 572 at 811 limitations. Nothing is really gained other than dissipation reserve if you run them as 811's. Forget about plate current limits in manual that are written for 811 tubes. Max safe current for a 811 is 175 ma per tube (though manual suggests a higher figure for tuning) The 572 is 275 ma per tube and while hitting 300 ma per tube or more briefly during tuning is of no concern for a 572, it would quickly melt a 811.

You could in theory convert a three tube AL811 into a solid desktop 800+ watt amp with a upgraded higher voltage supply for three 572's (say 2400 volts or so like using a SB200 transformer) and have a fairly solid amp. Not sure why Ameritron never built a new version of a two tube SB200.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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« Reply #72 on: September 07, 2017, 07:10:19 AM »

W8JX. You are definitely correct on the current. But if I recall from my past experimentation, the only way I would be able to get the same power out of the 3 vs 4 configuration, was to put more rf power in. Instead of 80w +/-, I think I was needing closer to 100w +/-. I'm sure that's no problem. Simply saying that tuning the 3 vs 4 with the same settings didn't have the same results. Neither did I think it should.

But again; I have a set of 4 572b tubes, so it's not a big deal for me to run all 4. Then again; I've never had any problems with running the 811a or G-811 tubes either. If a person already has 811a tubes in the amp, I wouldn't change them out. Not unless you wanted to have a spare set anyway. Or if you need new tubes; then I would definitely buy the 572b tubes. This way you'll never have to buy another tube again.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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« Reply #73 on: September 07, 2017, 07:23:44 AM »

W8JX. You are definitely correct on the current. But if I recall from my past experimentation, the only way I would be able to get the same power out of the 3 vs 4 configuration, was to put more rf power in. Instead of 80w +/-, I think I was needing closer to 100w +/-. I'm sure that's no problem. Simply saying that tuning the 3 vs 4 with the same settings didn't have the same results. Neither did I think it should.

But again; I have a set of 4 572b tubes, so it's not a big deal for me to run all 4. Then again; I've never had any problems with running the 811a or G-811 tubes either. If a person already has 811a tubes in the amp, I wouldn't change them out. Not unless you wanted to have a spare set anyway. Or if you need new tubes; then I would definitely buy the 572b tubes. This way you'll never have to buy another tube again.

The grid on a 572 are pretty rugged and 80w or more drive will not hurt three of them. The bigger concern with drive is the resulting plate current which can easily exceed a 811 tubes ratings. This is not a concern with 572's. That being said if you wish to run them as 811 then you should use 4ea 811's and not 572's as it is a waste of money. Because unlike using 4ea 811's which are easy to damage if even using Ameritron ratings, you will run out of power supply with 3ea 572's being pushed  before you hurt tubes. 
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WY7CHY
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« Reply #74 on: September 07, 2017, 08:09:37 AM »

So, in theory, you're saying that with 4 each 572b tubes in the amp (My choice because I already 4 on hand from my other amps), I could LEAVE my transmitter at 100 watts from when running barefoot; and tune up the amp with the 100 watts input. Obviously, tuned up in increments from say 20w to 60w to 100w or similar?Huh Or using a pecker, just leave the transmitter at 100w.

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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
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