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Author Topic: AL-811H with 572B tubes quick question  (Read 32384 times)
WY7CHY
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« Reply #15 on: August 23, 2016, 09:57:10 PM »

Yea, I put 4 each 572b's in the amp.

I agree that as long as I don't go beyond the rated 200ma grid current or the 750ma plate current; which I'm not near; I should be able to crank in the power in as much as it will take. I went past the 65 watts in and got the P-Out still going up. So tomorrow when I've got some time and can concentrate so I don't make any silly mistakes, I'll see how high I can get it without exceeding the grid or plate current.

Thanks for the input. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WY7CHY
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« Reply #16 on: August 24, 2016, 07:54:28 AM »

I had an hour or so before going to work this morning, so I decided to play with the power in a little on the amp. I watched the plate and grid current to make sure it didn't go too high. I got about 85-90 watts input, and I was able to get close to 600 watts out on RTTY. It was only drawing about 600ma plate current (Max allowed 750ma); and 150ma Grid current (Max allowed 200ma). I believe I could have still gone a little higher on the input power without maxing the plate or grid current. But the destruction manual says Maximum drive power permissible 85 watts. But I was real close to the 600 watts out. Depending on how accurate my wattmeter is. On a 3000 watt scale, it was close enough.

I did notice, from memory, that using the G-811 tubes, I got about the same plate and grid current, and basically the same output power, but with only about 70 watts input. So, using the 572b tubes, it required about an additional 20 watts input to produce the same output as the G-811 tubes. SOME may think this odd, considering the 572b tubes are suppose to be a stronger tube. I personally think this sounds about right, considering the 572b WANTS to have about 2500 volts going to the plate, and it's only getting 1600-1700 volts from the AL-811H.

So, if the plate and grid current are still below allowable tolerance, I don't think pushing more rf input power "Should" negatively affect the amplifier. Definitely not the tubes, but most likely nothing else either. That however is simply speculation based on math. I'll do some more experimenting when I get home tonight. The fact that I can get 600 watts out RTTY with 600ma plate and 150ma grid with 65-70 watts using the G-811 tubes, tells me that they probably aren't being pushed too hard. Same with the 572b's, same current but more rf input power still isn't stressing the tube.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WD8T
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« Reply #17 on: August 24, 2016, 08:35:52 AM »

You only need to run 3 of those tubes to get full output and not all four 572's.  Save one for a spare.
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W3RSW
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« Reply #18 on: August 24, 2016, 08:39:09 AM »

What you might want to do is tune and load your 572b's at several points of plate current Ip required at 100, 200,300... 600 watts points out on your existing 1600 plate input voltage, Ep.

Read the plate current Ip for each wattage point and plot that Ip vs. Wattage output at each wattage point on a piece of semi-log paper. You will get a straight slope until a sag point at high loading.  But for estimation purposes, now go to tube spec tables and find what current is required at the nominal 600 watt point at the 572b's 2500 Ep rating. Plot that point and overlay the previously found slope from it.  You'll now have two approximate parallel slopes, giving Ip vs. Wattage for each nominal power supply voltage .  They won't actually be parallel but at the mid current points will be close enough.  If you don't find an exact 600 watt point in tube specs fine whatever the greatest Ip is at whatever power out and plot that.  Better yet, a tube spec sheet may have several power points already listed. Your overlain slope from the lower Ep will tell the rest.

You'll find a sag beginning  in the semi log slope when overloaded. The knee of the slope tells the tale when tubes run out of poop.

I see Svetlana shows a 600 watt point at Ip @ 375 ma, Ep @ 2750 VDC, Pin @ 600 watts ( single tube), Pd @ 160 watts which yield 440 watts output, given perfect tank circuit, etc. and a 50 ma grid current.  So a couple of them at 2750, no sag should yield over 800 watts (880 perfect.)

« Last Edit: August 24, 2016, 08:54:35 AM by W3RSW » Logged

Rick, W3RSW
WY7CHY
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« Reply #19 on: August 24, 2016, 11:00:09 AM »

I appreciate the input. I know that the weak link in the AL-811H (As well as it's siblings in all the AL-811 series), is the power supply. It's simply not going to put out anything significantly about 600 watts CW/AM/RTTY or 800 SSB. Technically, the 572b tubes can handle putting out a lot more. E.g. The Ameritron AL-572 uses 4 each 572b tubes and is rated for 1300 watts. But that amp doesn't have the light weight 1700v plate volt power supply.

So even though I'm putting 572b tubes in place of the 811a tubes, there are still some things I should be concerned about. Hence, the reason for starting this thread and seeing if anyone could input some things they've noticed when doing this that I should be aware of. Mainly, you still don't want to exceed the max plate or grid current. Not just because of the tubes; which the 572b probably could handle, but the other components in the amp. An amp isn't simply a power supply and tubes. Same with the RF power input. While with 811a tubes I push 65-70 watts into it, and I can get 600 watts out in RTTY mode, for me to get the same 600 watts out using 572b tubes, I've found that I need to input about 85-90 watts. This is actually understandable, considering that the 572b tubes aren't being powered by nearly as much plate voltage as it WANTS TO HAVE. This isn't a big problem, but I don't want to really go beyond 85-90 watts input. Even if the plate and grid current are still low enough. There are other components that could be affected with too much input. IMD, Splatter, other forms of distortion, etc.

Some people have claimed that the 572b from 811a was a simple tube swap. That everything else was almost identical. Same amount of input power, same amount of voltages and current. That's fine. Obviously, it's not always like that. So, what I have concluded from this experiment?

FOR MY AMP WITH MY SET OF 572B TUBES AND MY SITUATION: (Could be different for others)

1. To get 600 watts output in RTTY mode tuning, either the 811a or 572b tubes, will draw approximately 600ma plate current; 150ma grid current; 1400v Plate Voltage.
2. That is approximately 840 watts input (1400v x .150a). With 600 watts output, that leaves about 240 volts of heat dissipation.
3. That means each tube is dissipating approximately 60 watts in heat. For the 811a, that's close to the 65 watts max it's capable of. The 572b can handle 160 watts. (In someone else's scenario, if they were drawing 1500v plate voltage on key down or more than 600ma plate current on key down, then you would definitely surpass the 811a capabilities. Still not a problem for the 572b).
4. The 811a tubes required 65-70 watts input from the transceiver; the 572b required 85-90 watts to be almost identical.
5. In THEORY, just based on MATH, in MY SCENARIO, with MY TUBES, the 572b tubes would be less stressed and should perform longer.
6. In THEORY, inputting 85-90 watts from the transceiver to the 572b tubes, could possibly put in some distortion, splatter or something similar. It is at the MAX RECOMMENDED input for the amplifier. I do not accept that the max input power from the transceiver is based solely on plate and grid current to the tubes, but also other components in the amp that may be affected by too much input RF power.
7. So for my situation, with 811a tubes, I am pushing the max dissipation that the tubes can handle.
8. So for my situation, with 572b tubes, I am NOT pushing the max dissipation that the tubes can handle, but I MAY be pushing the max RF Input from the transceiver that the amp's other components can handle.
9, So for my situation, where I ONLY OPERATE on SSB, either tube and either situation would be fine, because the duty cycle is so much lower in SSB and the amp should/would be able to handle either one just as well.
10. And no one can definitely prove whether or not the 572b will last any longer than the 811a tubes will. At least enough for an ROI of the cost difference between them and the 811a. Mathematically, you'd think the 572b tube should last longer. But in theory, running a tube (572b) at such a lower voltage from what it wants, could affect it's long term performance. I owned a porsche as well as some other european sports cars. If I ran them only in town, for more than 2 weeks, it would really start to run like crap. It needed to be on the autobahn doing 100mph.

Anyway; these are my observations. They apply to MY amp; with THIS SET of G-811 vs 572b tubes. Other's mileage may vary. Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
N9AOP
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« Reply #20 on: August 24, 2016, 12:30:34 PM »

Why so much worry about the life of the 572B.  I used the 811A for MARS nets and the 572B tubes ran 5 years at 10 hours a week year around.  They are still in use with the ham who bought the amp. 
Art
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WY7CHY
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« Reply #21 on: August 24, 2016, 01:11:49 PM »

I have an AL-811H amp. It has some very good G-811 tubes in them. (Ryazan - Same manufacturer as Svetlana). While on another thread, the "On-Going-Debate" was on by certain people that the 811a tube sucked; that using it in the AL-811H amp at rated specs was extremely stressing the tubes. That at best, it wasn't a 600w CW/RTTY  or 800w PEP SSB amp, but closer to the 400w range. And IF, IF, IF you must have an AL-811 family of amplifier, then you should definitely get the 572b tubes, because those tube will allow you to get the same power; actually with 3 instead of 4 tubes; and that the tubes won't be stressed with dissipation because they are rated at 160 watts plate dissipation vs 65 watts on the 811A tubes.

I've used a lot of 572b tubes in other amps, but I never tried swapping an 811a for them. A friend of mine had 4 NOS, never used, Taylor's. He owed me some favors, so he sent me 4 to experiment with and keep if I wanted. So, I put in the 4 572b tubes and commences checking them out and coming up with an opinion. I started this thread to get some inside from previous people who have put in 572b tubes in place of their 811a tubes to see what to expect. As I asked in my original post; would it require more input power from the transceiver? Would a break in/getter be required? With the 572b having so much less plate voltage than what it's designed for, would that affect the output? etc.

Not sure if you read the beginning of the thread, but that's what this is about. Whether the thread evolves into more/something else; "Like MOST threads do"; we'll see.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
KD6VXI
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« Reply #22 on: August 24, 2016, 03:44:47 PM »

They have a higher mu,  but the figure of gain is at operating voltages.

With the anode voltage dropped,  you'd have to expect gain to drop from 2.7 kv figure.

You need to drive it harder.   Watch grid current (if you can),  don't exceed max for the 572s.

You will probably put out a cleaner signal with your exciter putting out closer to a hundred watts pep.   Most powered by bipolar devices fall apart (as to imd)  when lowering Pout.   Sometimes by 10 to 15 db.   Then,  shove that all new dirtier signal into your amp,  and your transmitting feces quite quickly.

American makes / made a 572 based 811 chassis.   I'd download the manual and run your amp with the 572s in it as that manual states.   

--Shane
KD6VXI
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W1QJ
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« Reply #23 on: August 24, 2016, 03:45:20 PM »

With just about any triode tube in a GG amplifier, the gain of the tubes drop as you move lower in plate voltage from its "typical to max rating".  It would stand to reason that the 572B tubes would require more drive than usual to put out a certain level of power when run at a lower plate voltage.  In the 811H the plate voltage is about 1000 volts less that the 572b's tube normally run.  Used properly the 811 tube run fine.
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WY7CHY
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« Reply #24 on: August 24, 2016, 03:58:00 PM »

Totally agree. When run properly, the 811a tubes run fine. I did this more as an experiment because it didn't cost me anything.

I did look at the destruction manual for the AL-811HD which is the same amp as mine, except supplied with the 572b tubes. Unfortunately, all of the destructions are identical. Including the part about not exceeding 85 watts input.

But I totally agree, that based on the 572b specs, and the much lower voltage on the plate than what the 572b wants, you'd have to put more drive into them. My only concern with pumping more than the 85 watts into it, is that the amp is more than just a power supply and tubes. There's the tuned circuits, and other components. It's possible, but no one seems to know, that pushing 100 watts from the exciter while not hurting the tubes at all, could possibly cause splatter, distortion, inter mod, etc because of the other parts of the circuit that weren't designed for an excess of 85 watts. But that's pure speculation. I no longer have a o'scope to check it out with.

I'll try it at the 85 watts level for a while. In time, I may try cranking to max out of the exciter, 100 watts, maintaining below 750ma plate current and below 200ma grid current. Just to see what happens. Thanks for the feedback.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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« Reply #25 on: August 24, 2016, 04:54:43 PM »

Totally agree. When run properly, the 811a tubes run fine.

The BIG wild card here is run properly and using Ameritron OEM specs is not properly using 811 tubes

But I totally agree, that based on the 572b specs, and the much lower voltage on the plate than what the 572b wants, you'd have to put more drive into them.

Not true at all unless tubes are soft. (from being abused by being over driven) Same drive should yield same output as 811 but 572 can be safely driven much harder. I get about 1000 watts out with 55 watts of drive into four 572's  at 1800 plate volts (CW Mode) on My Dentron. Increasing plate voltage to 2600 (SSB Mode) give 300 watts more with same drive. I normally run 1800.

I'll try it at the 85 watts level for a while. In time, I may try cranking to max out of the exciter, 100 watts, maintaining below 750ma plate current and below 200ma grid current. Just to see what happens. Thanks for the feedback.

Once again WAY TOO MUCH DRIVE!!  Not sure what you think you are gaining??? You are degrading audio and reducing linearity at the sake of trying to get a few more watts that make zero difference down range. You will sound better with less drive but I think you are on a wattage trip of sorts.  With good tubes you should need 40 to 50 watts drive for about 450 to 500 out. Basically you figure on about 10 db gain when tubes are good and are driven properly and linearity is being maintained. When you push drive higher linearity goes out the windows and audio quality with it.
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WY7CHY
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« Reply #26 on: August 24, 2016, 05:12:36 PM »

Well, it is possible that even though these are NOS tubes, and I guarantee they've never been used before I put them in, that they could be soft. But with the 65-70 watts input with the 811a vs the 572b, the 572b produced about 100 watts less.

Personally, I don't know how a tube that's designed to have so much more plate voltage, is going to put out the same output with the lower voltage. Based on what you say about getting 1000 watts out with 55 watts in and 1800 volts plates, and you saying the 572b should put out the same as the 811a with the same, then you're saying both the 572 and 811 only need about 30 watts in to get 600 out. Sorry, but I just don't see it. Unless you didn't explain properly.

Even according to Ameritron, it takes about 65 watts in the al811h, with 811a tubes, to produce 600 watts. You're saying with the same voltage, you can get 1000 watts out with 55 watts in?  Don't see it.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
VK3BL
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« Reply #27 on: August 24, 2016, 06:46:07 PM »

Does your amp have input swamping resistors like the later AL series?  If so, thats the reason you drive power could be a lot higher than what others expect it to be.

For example, the old AL-811 required about 40 watts drive for full power, the new one requires 55 watts+, and this is in the 3 tube model.

Comparing drive powers between different amps makes absolutely no sense at all - even across the same family where circuit changes can and do happen on the production line.

If you're just running SSB Phone, put what you want into it as long as you stay linear.  A peak of 100 watts is going to do no more harm than a peak input of 85 watts.  Remember, these are just peaks - the average drive power will be around 20-30 watts, much lower than the continuously rated drive power of the amplifier.

I honestly don't understand the obsession with drive power to be honest - its linearity that really matters.

Check out Tom's website on the topic:
http://www.w8ji.com/al811h_schematic.htm
« Last Edit: August 24, 2016, 06:48:22 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
WY7CHY
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« Reply #28 on: August 24, 2016, 07:28:09 PM »

There's no obsession here. Remember; from the original post, this is an experiment based on opinions that the 572b tube would be better than the 811a tube in the AL-811H amp, because the 811A tubes mathematically are being pushed to their limit. I had access to 4 NOS 572b tubes; guaranteed to not have been ever used. It didn't cost me anything.

My finding; were that at the same input power as I was using with the 811A tubes, these 572b tubes were producing approximately 100 watts LESS POWER.

My confusion in the last few posts, are with what JX had said. That in his Dentron, he can run 4 each 572b tubes, with 55 watts input, and get 1000 watts out. I just don't see it. Even in Tom's supplemental tuning instructions, he has a minimum of 60 watts going in, just to get to the 600 watts out. Ameritron says normal input of 65 watts to get rated 600 watts out. Granted, these are 811a tubes, but they should be that different. I'm confused how JX is getting 1000 watts out of 4 572b tubes with 1800 volts plate and 55 watts in.

I'm not sure if I have the swamping resistor. I know this amp isn't the newest one, but it does take around 65 watts for the rated output. Yet, it has some older inside parts that aren't in the newer amps. Like the older style parasitic that wasn't a circuit board. And 210uf hv caps instead of the 270uf. etc. I'd have to look for the swamping resistor. But in both sets of 811a tubes, to get the 600 watts, it is about 65 watts input.

The fact that Tom, (The inventor), and Ameritron both say you need about 65 watts average, and max around 85 watts for rated output power; (Which sounds accurate to me); makes me believe that more than thinking 40-50 watts max is what I should be using.

And I agree; if using SSB, it really doesn't matter. I can tune up the amp with 85 watts to get the rated 600 watts cw/rtty, and when I flip it to SSB mode, it is not going to be a problem.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
VK3BL
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« Reply #29 on: August 24, 2016, 10:36:20 PM »

There's no obsession here. Remember; from the original post, this is an experiment based on opinions that the 572b tube would be better than the 811a tube in the AL-811H amp, because the 811A tubes mathematically are being pushed to their limit. I had access to 4 NOS 572b tubes; guaranteed to not have been ever used. It didn't cost me anything.

My finding; were that at the same input power as I was using with the 811A tubes, these 572b tubes were producing approximately 100 watts LESS POWER.

My confusion in the last few posts, are with what JX had said. That in his Dentron, he can run 4 each 572b tubes, with 55 watts input, and get 1000 watts out. I just don't see it. Even in Tom's supplemental tuning instructions, he has a minimum of 60 watts going in, just to get to the 600 watts out. Ameritron says normal input of 65 watts to get rated 600 watts out. Granted, these are 811a tubes, but they should be that different. I'm confused how JX is getting 1000 watts out of 4 572b tubes with 1800 volts plate and 55 watts in.


I wasn't implying you had one Mike - just in general it seems to be bandied about a lot when people are comparing apples and oranges, and that doesn't make sense to me.

I can't see 4x 572B tubes @ 1800v loaded making 1000 watts with 55 watts drive - my Ameritron AL-572 needs 2400v loaded and around 80 watts of drive to make that...

But, like I said.  Comparing the drive requirements of apples to oranges is just silly - the design of the amplifier does play a significant part in drive requirements.

Anyway, it certainly is interesting to learn you need more drive with the 572B tubes to achieve the same power level.  I really wouldn't have though that would be the case, but who cares really? You won't damage anything feeding them with even 100 watts SSB.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
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