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Author Topic: AL-811H with 572B tubes quick question  (Read 32356 times)
WY7CHY
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« on: August 22, 2016, 08:10:47 PM »

I've used the 572b tubes in a FL2100B and a SB200. But with all the pro-con comments about using 572B tubes in a AL-811H, I decided to try it.

A friend sent me a set of 4 NOS taylor 572B tubes. I've installed them and am letting them heat for a few hours before working them. I know because of the AL-811H power supply, I am not expecting to get more power out. But I have a couple of questions that I haven't really been able to find answers to from searching. Basically wanting to know what to expect.

1. Because the 572B will never get to the voltages in a AL-811H that it can handle, is there any gettering for the tube? Is it even worth trying or should I just start using the amp.
2. Because the 572B is use to a lot more voltage, will it require more wattage input from the transceiver to equal the same amount of output from the AL-811H when using 811A tubes.
3. Would it be possible that using 572B tubes could produce a lower amount of power out of the AL-811H vs using 811A tubes. Considering it isn't getting the voltage it wants.

Like I said, I haven't started transmitting on it yet, but I'm wanting to know what to expect. I would think, with a lot less voltage than what the tubes can handle, that the output power might be less. Or it might at least require more input power. E.g. 80 watts in vs 65 watts with 811A tubes. My tubes prior have been Russian G-811 Ryazan. They worked fine. But with all the controversy about the 811A tubes being pushed beyond their specs, and 572b supposedly better, I thought I'd give the 572b a try. Not costing me anything. Just wanting to know what to expect. Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W4JCK
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« Reply #1 on: August 22, 2016, 10:20:01 PM »

I will relate my experience with the same scenario.  I'm sure those with more tube expertise will chime in along with those who disagree with using 572s.
After I got my 811H, some years ago, and reading about the nature of the Chinese 811As, I bought a set of 4 Svetlana 572s from RF Parts for $140.00.  It seems the Svetlanas are gone now and the current 572s will cost quite a bit more.

I did it primarily because I was doing quite a bit of 40m and 20m AM operation and quite a bit of 20m SSTV.

These modes are a little tougher on the tubes than CW and SSB.  Would the 811As have also worked?  Probably, but perhaps again, not for too long.  I don't really know.  What I did know was the 572s were likely loafing along and the only really stressed area was probably the power supply.

As far as drive power, I tested with the 811As before I swapped them and then with the 572Bs.  There was perhaps 5 to 10 watts difference required and it wasn't consistent as far as one type requiring more.  It was band dependent.

As far as operating, I let mine run-in over a couple of 8 hour power on/off cycles before transmitting.  That's just in my anal retentive nature - it may not be necessary.

And yes, don't expect any real power increase unless the original tubes were weak.

Good luck with your amp - I suspect with the waning cycle, you'll enjoy having it.
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W1QJ
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« Reply #2 on: August 22, 2016, 10:34:34 PM »

Letting  the tubes just stay on for hours does nothing.  That's just a waste of time.  These tubes only have their getter activated when the plates are hot. 
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WY7CHY
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« Reply #3 on: August 22, 2016, 10:35:24 PM »

Thanks for the input. After a couple hours on, I decided to tune up 20m. I didn't want to see what max power is, yet. I only tuned up with about 20 watts input. Wanted to make sure the tubes were producing power. I did notice that plate current, with no input power, seemed a little low. At least lower than with the G-811. But I didn't do much of a test yet. I shut it down for the night and I'll heat them up tomorrow after work.

Like I said, I'm familiar with the 572b, but with amps intended for them. I'm curious to know what to expect from putting them in the al-811h. Difference in Current; Difference in input power required; etc. Thanks for some insight. mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
WY7CHY
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« Reply #4 on: August 22, 2016, 10:40:19 PM »

Letting  the tubes just stay on for hours does nothing.  That's just a waste of time.  These tubes only have their getter activated when the plates are hot. 

Thanks for that. Honestly; I wasn't sure that with so much lower voltage; 1600v vs 2500v +/- that there'd be much ability to getter. Maybe it doesn't need that much voltage to getter.

I'll probably go ahead tomorrow and start using it. I've known some tubes that actually condition and get better with more output after a number of hours using them. Either way, with the AL-811H having much lower voltage, there's probably little chance of hurting the 572b from using them.

Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
VK3BL
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« Reply #5 on: August 22, 2016, 11:54:32 PM »


1. Because the 572B will never get to the voltages in a AL-811H that it can handle, is there any gettering for the tube? Is it even worth trying or should I just start using the amp.
2. Because the 572B is use to a lot more voltage, will it require more wattage input from the transceiver to equal the same amount of output from the AL-811H when using 811A tubes.
3. Would it be possible that using 572B tubes could produce a lower amount of power out of the AL-811H vs using 811A tubes. Considering it isn't getting the voltage it wants.


1) They won't getter on idle - plate voltage is irrelevant.  Still, can't hurt to let them 'warm up' a bit, I feel.

2) I'm not sure, but from what I have read the 572Bs have a mu around 190, vs the 160 for 811As.  Therefore, all things being equal, the 572B has more gain and should need LESS drive.

3) I would expect power output to remain the same.  The lower voltage just means you can't push the tubes as hard.

Lastly, some suggest that running at lower voltages the tubes won't getter correctly, and life will be shortened.  I do not believe this to be the case.  So long as you run some high duty cycle modes such as AM, CW, RTTY, PSK31, JT65 etc, you should still be able to heat the plates up enough for a faint red glow and activate the getter.  If not, just slightly misload the amp into a dummy load every now and again to produce the red glow.

On a final note, do your best to *never* get a red glow of any kind when using 811As, in my experience it is bad news for their lifetime.  Its worth noting that this SHOULD NOT be the case with 572Bs, as they have graphite plates like the 3-500ZG. 

Good luck with the 572Bs, and be sure to share your experiences Smiley

Oh yeah, and watch out for neutralisation issues - the 572Bs have different interelectrode capacitances and it would be good practice to re-neutralise your amplifier now that you have swapped tubes.  Ameritron should be able to walk you thru the procedure.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
G3RZP
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« Reply #6 on: August 23, 2016, 03:40:13 AM »

The RCA book says that both the 811A and 812A show a 'barely perceptible red color' on the plate at maximum ICAS rating - and no 'color' at full CCS rating. So on SSB voice, I would expect it not to show red at all.
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N9AOP
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« Reply #7 on: August 23, 2016, 10:02:22 AM »

I had an 811H for 10 years and used both 812a's and 572b tubes and never had an issue.  In the beginning it didn't matter because you could re-tube it with 811's for pocket change.  The fellow I sold the amp is still using it every day with the 572's which came from RF parts about 6 years ago.  If you are a real klutz at tuning the amp, the 572's would probably serve you better but if not and you operate the amp conservatively, the 811's should last.
Art
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WY7CHY
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« Reply #8 on: August 23, 2016, 12:14:34 PM »

I appreciate the feedback. Are you able to give any insight on the questions I had?

1. Do you need to do any real break in or gettering of the 572b tubes, or just go to town with them?
2. Does the 572b tube require more input power to produce the same output power; being they don't have the voltage they are use to. E.g. input 80w vs 65w to output the same wattage?
3. Being the 572b tubes are running lower voltages, is it possible that the 572b may actually put out less wattage than an 811A.

I'll be transmitting them tonight when I get home. Last night, I just let them cook for about 4-5 hours. Just wondering what to expect. Thanks. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
KD0REQ
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« Reply #9 on: August 23, 2016, 01:05:08 PM »

as for the lower voltage, I read a fair number of "starved plate" stories using 250-volt range tubes down to 9 volts on the plate with receiving tubes.  occasionally less. if it works, don't sweat it. plate dissipation is what getters the tubes, and if they get hot enough, it will happen.

Ameritron now and again (the ad is back in the last QST) sells a version of the 811H with 572Bs already in it, so it can't be the road to ruin.
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N9AOP
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« Reply #10 on: August 23, 2016, 02:07:55 PM »

Again, I ran the 811H for 5 years with the 811's and 5 years with the 572B's.  I never did anything except put them in and operated normally.  The newly manufactured tubes should run right out of the box without any burn in.
Art
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WY7CHY
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« Reply #11 on: August 23, 2016, 04:35:32 PM »

Well, I looked at the tubes before firing it up again today. Looks like they are/have gettered. Brand new they were nice and clear. Now have mirroring on the glass next to the getter.

I fired them up and tuned it up. It tunes fine. Nothing spectacularly different. I have noticed that with the same amount of input from the transceiver, there is less output on all the bands. With 65 watts in with the g-811 tubes, I could tune to 600 watts on rtty. With the same 65 watts in and the 572b tubes, it's around 500 watts. Maybe the tubes need more time. Not the worst thing in the world. Plate current with the g-811 on rtty was around 600ma plate current, with 600 watts out and 65 watts in. With the 572b tubes, around 500ma plate current, with 500 watts out and 65 watts in.

I'll keep checking for a week or so. Depending, I may keep them in, or go back to using the g-811 Ryazan tubes. Thanks for the info. Mike.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
VK3BL
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« Reply #12 on: August 23, 2016, 06:15:32 PM »

Well, I looked at the tubes before firing it up again today. Looks like they are/have gettered. Brand new they were nice and clear. Now have mirroring on the glass next to the getter.

I fired them up and tuned it up. It tunes fine. Nothing spectacularly different. I have noticed that with the same amount of input from the transceiver, there is less output on all the bands. With 65 watts in with the g-811 tubes, I could tune to 600 watts on rtty. With the same 65 watts in and the 572b tubes, it's around 500 watts. Maybe the tubes need more time. Not the worst thing in the world. Plate current with the g-811 on rtty was around 600ma plate current, with 600 watts out and 65 watts in. With the 572b tubes, around 500ma plate current, with 500 watts out and 65 watts in.

I'll keep checking for a week or so. Depending, I may keep them in, or go back to using the g-811 Ryazan tubes. Thanks for the info. Mike.

Are you sure they are NOS tubes?  As previously mentioned, the 572B is a higher mu tube than the 811A, so I would have expected a higher output for the same level of drive.

That said, don't feel like you are limited to 65 watts of drive.  In my AL-572 (the AL-811's big brother), I use 100 watts to get 1200 PEP out into a dummy load, which is considered normal.

If you find that the 572Bs don't produce as much power as the 811As at any drive level, I would suggest they are weak / not NOS.  Bare in mind a tube can look NOS but still be down on emissions.  I have a few Ryazan G-811s that I ran really really hard that look as good as the day I got them but are definitely down on emissions.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
WY7CHY
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« Reply #13 on: August 23, 2016, 07:11:21 PM »

I appreciate the input. The 572b have a getter. that usually leaves that common mirror look on the side of the glass near the getter material. The tubes NOW have that on them from operating for a total now of about 6 hours. 3 yesterday and 3 today. OUT of the BOX, they were perfectly clear.  I'm pretty sure they were NOS.
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
VK3BL
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« Reply #14 on: August 23, 2016, 07:50:22 PM »

I appreciate the input. The 572b have a getter. that usually leaves that common mirror look on the side of the glass near the getter material. The tubes NOW have that on them from operating for a total now of about 6 hours. 3 yesterday and 3 today. OUT of the BOX, they were perfectly clear.  I'm pretty sure they were NOS.

Yeah thats fair enough Mike.  I am just curious as to why you'd see lower Pout, when they are meant to have a higher mu.  That said, we're talking about decades old datasheets here that probably don't apply.

What is the maximum Pout you can get?  Don't be afraid to go beyond 65 watts of drive - as long as your Pout increases remain linear, and you don't exceed grid dissipation, you won't have any issues.

Also, just confirming you put 4x 572B tubes in the amp rather than 3? 
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
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