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Author Topic: 811H problem  (Read 7968 times)
AK4QA
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Posts: 31




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« Reply #15 on: March 14, 2008, 10:52:35 PM »

right right...not a problem as I only have one arm!

whoever said, 'stop,drop and roll" aint never been on fire before.  

It turns into, "OH #@%$ and RUN!!", in a HURRY!!

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WT0A
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Posts: 922




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« Reply #16 on: March 14, 2008, 11:02:05 PM »

Lee
Inside the amp on he plate that the tubes are mounted on there are 4 2 watt resisteor. If one is open then the tube did indeed have an "event" and the 500 max out sounds about right for one tube not functioning. I can email u my phone # if you wish.
Glen
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WA1RNE
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Posts: 1010




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« Reply #17 on: March 15, 2008, 07:46:56 AM »

 "Looks like 475-500 across all the bands. How do I tell a bad tube? The look the same thru the vent, IMHO."


 >>> I doubt you have a bad tube - or have a significant performance problem with this amplifier, unless you continue to experience the previous event where grid current was pegging with 60 watts of drive.

 
 Take a close look at the specifications:  the output rating is 600 watts CW, 800 watts PEP (SSB).

 The power supply runs at 1700 vdc no load, 1500 vdc full load, or about 12% regulation which is pretty decent. The manual indicates not to load the amplifier past 450 ma plate current, or 675 watts input. Since the plate dissipation rating on each 811A is 65 watts intermittent (ICAS), x 4 tubes or 260 watts, 415 watts plus any driver feed-through in grounded grid service puts you at about 475 watts - about what you are seeing, and within the maximum ratings of the 811A's.

 The manual also states, quote:

 Output (7MHz)

Typical SSB PEP voice operation: over 800 watts continuous
Typical CW continuous operation: 600 watts
1/2 hour PEP two tone: 650 watts
1/2 hour continuous carrier: 400 watts

 
 This is, IMO a little ambiguous. As you can see from the above analysis, obtaining 600 watts out on CW is a bit of a stretch, especially on 80 if the output circuit lacks enough loading, as well as on 10 meters where the efficiency of the tube begins to taper downward.

 BTW, the manual appears to have a significant error in the CW tune up instructions. In section 8, page 6 it indicates not to exceed 450 ma plate current, but a note at the bottom of the page indicates not to exceed  * 750 ma * plate current - about 72% more dissipation than 811A's can stand.

 So the only time you can expect to see anywhere near 800 watts is in SSB service where power supply dynamics allow higher, short term peak input conditions to exist, which is also dependent the peak to average ratio created by your speech characteristics.

 
 ...WA1RNE
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K7KBN
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Posts: 3676




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« Reply #18 on: March 15, 2008, 12:02:43 PM »

Lee:  No offense intended (and from your response, you certainly didn't take any offense ;>) ).

"Women and children first, right after me!"

73
Pat K7KBN
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73
Pat K7KBN
CWO4 USNR Ret.
N3JBH
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Posts: 2358




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« Reply #19 on: March 15, 2008, 12:10:42 PM »

"BTW, the manual appears to have a significant error in the CW tune up instructions. In section 8, page 6 it indicates not to exceed 450 ma plate current, but a note at the bottom of the page indicates not to exceed * 750 ma * plate current - about 72% more dissipation than 811A's can stand."

Well i guess that makes sense why W8JI has made many comments such as this,


" I'm one of the people who thinks replacing 811's with 572's is often a good idea."

"The reason is 811's are severely dissipation limited. So if you mistune or run the amp a little hard at times, you can quickly kill a set of 811A tubes. The tubes are indeed the limiting factor in reliability or life in virtually every 811 based amp I've even seen."

"With four 811's you have about 260 watts dissipation which is good for 520 watts out"  

"Virtually all 811 amps are severely dissipation limited, so anyone not able to tune in a matter of a few seconds or who runs a high duty cycle would be well-advised to look at higher dissipation subs.
73 Tom "

And being Tom has had his hand in the design of the AL-811 series amps i would tend to listen to him.
So add the 572 tubes and dont sweat the problem. Jeff

My Thanks to Tom W8JI for making all the information freely open to us. You can read all of Toms words at.
http://www.eham.net/forums/Elmers/177374
I only took what i felt was needed to answer the question or statement as was stated.
Jeff

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WA1RNE
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Posts: 1010




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« Reply #20 on: March 15, 2008, 02:28:34 PM »

 
 "Well i guess that makes sense why W8JI has made many comments such as this....." etc., etc.


 >>>  Jeff, what has this got to do with KE4VYN's issue?

 He's questioning the amount of CW output power versus the PEP output rating of the 811H amplifier, as well as a single instance of very high grid current.


 You're sighting technical advice from W8JI that dealt with a totally different question and post, presented by NC1E on the Elmers forum concerning the use of 811A's versus 572B's.

 
 ...WA1RNE
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AK4QA
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Posts: 31




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« Reply #21 on: March 15, 2008, 03:01:52 PM »

WA1RNE,
You got me thinking that I in fact might not have a problem.

Facts;
1. I was increasing power with no ALC control.
2. First time this radio, with me has been connect to a amp.
3. Still working.  (no shorted tubes or blown fuses)

Questions;
1. could a spurious power burst from radio at max limits over drive and 'flash' a tube?
2. Can a tube survive a 'flash'?
3. Could coil arcing be misread as flashing?
4. Could 500 watts RTTY out just be what this amp does,
and SSB actually be within 600-800 watt range.

AND LASTLY, should I worry or just run the thing?

thanks
Lee
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N3JBH
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Posts: 2358




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« Reply #22 on: March 15, 2008, 03:33:07 PM »

"Jeff, what has this got to do with KE4VYN's issue?"

Really it had nothing much to do with it at all. other than you brought up the specs on that tube. And from what i was able to make on it was suggesting that he would be beating the snot out of his amp if he did indeed run the plate up to the .750Ma limit.

You seem to have implied from how i read it that the .450Ma rating was the correct rating to use. Now i am not certian if you have used the amp in question or not but i am and i have run the Plate upto that .750Ma many times with out a failure of any type.

I am still using the same old stock tubes it came with. will i change to the other ones? Most likley yes when i finally kil the ones i have now.

But to answer the main question the gentleman has i simply asked him what his readings was and on what bands he had the problem? He replied that it was on most bands if i recall. I simply wondered if he added some heavier Loading to drop the grid down was all.

But when i read your statement about the tube and Typo on the manual i thought it be a good time to interject that coment was all. I did not see where it was in harm.

Futher more The manual really is not clear if you ask me as to quote the manual on page 6 step 8 it reads.

"8. Apply only enough drive to indicate a grid current of100mA, or an Ip of no more than 450mA. Tune the
PLATE control for maximum output power. It is normal
for the plate current to dip at this point. If the grid current
goes over 200mA, reduce the drive at once. Unkey the
exciter."

It never states this is the maxium reading there does it now?

I read it as it is suggesting to tune it up to that level and stop and check readings !!! Then it goes on to state and i quote

"9. Observe the output on an external RF wattmeter. Increase
the drive until full exciter power (never to exceed 80 watts)
or 200mA of grid current, is achieved. Quickly adjust the
PLATE and LOAD controls for maximum output power.
10. Reduce the drive until the desired output levels are
obtained.
NOTE: Rotating the LOAD control clockwise reduces grid
current for a given amount of drive. If the LOAD
control is set at too low a numerical setting, a severe
stress on tank components may occur. The PLATE
control should always be peaked for maximum grid
current or output power. Do not exceed 750mA of
plate current during tune-up"

Now that tells me that you can go on and adjust it for maxium power out but do not go over .750Ma.

So there my Dear freind did i explain my self ok now Huh? Jeff
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N3JBH
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Posts: 2358




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« Reply #23 on: March 15, 2008, 03:40:44 PM »

Lee
 If you are getting 500 watts out on rtty i would say your good to go in my opion. My other opion on this matter is if your using 811-A tubes and running 500 watts on rtty. you may be kind of hard on them tubes. A email i got from Ameritron said that if i wanted to run Rtty or other modes like such. That i should consider replacing the tubes with 572-B tubes and even then stay below 450 watts out.

I am sure there be response to this but just going by what they stated. And while i admit i do not remember where on eham i placed that email. It is indeed on here some place in its orginal form

Jeff
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N3JBH
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Posts: 2358




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« Reply #24 on: March 15, 2008, 03:43:28 PM »

Now WA1RNE did that make you happy? See i adressed you and Lee both now. Now we can all be happy get along and go play radio.
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WB2WIK
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Posts: 21836




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« Reply #25 on: March 15, 2008, 06:08:18 PM »

>RE: 811H problem  Reply  
by KE4VYN on March 15, 2008  Mail this to a friend!  
WA1RNE,
You got me thinking that I in fact might not have a problem.

Facts;
1. I was increasing power with no ALC control.
2. First time this radio, with me has been connect to a amp.
3. Still working. (no shorted tubes or blown fuses)

Questions;
1. could a spurious power burst from radio at max limits over drive and 'flash' a tube?<

::Maybe.  But the "flash" may not have been a tube, it could have been a capacitor arc -- symptoms are similar and capacitors recover provided the arc didn't leave a sharp spot on the capacitor plate.

>2. Can a tube survive a 'flash'?<

::Tubes survive internal arcs.
 
>3. Could coil arcing be misread as flashing?<

::Don't know why a coil would arc, although the plate RF choke could develop a hot spot -- if you look carefully at the whole length of its winding you might see if that happened.  More likely a capacitor, although if operated into a dummy load the voltage across the LOAD cap (the closer spaced one, more likely to arc when faced with a mismatch) should never be very high.
 
>4. Could 500 watts RTTY out just be what this amp does,<

::Should do about that; with a stiff 240V line for power, usually higher.  
 
>and SSB actually be within 600-800 watt range.<

::800W PEP is easier to accomplish but of course you need a true PEP meter to measure that.  A normal Wattmeter cannot.

>AND LASTLY, should I worry or just run the thing?<

::I'd just use it.  If it's new and actually fails, you've got warranty coverage.  If it seems to tune normally on all bands with a dummy load, it's probably fine.

An "event" while using an *antenna* and not a high power rated dummy load could actually have been caused by an antenna arc (outside, you wouldn't see it, but the amp would notice) if this is the first time you've ever run higher power with that particular antenna.  If this happens, you'd see not only a spike in grid current but also a spike in VSWR if you were watching that at the time.

WB2WIK/6  
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WA1RNE
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Posts: 1010




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« Reply #26 on: March 16, 2008, 07:59:58 AM »


 "Could 500 watts RTTY out just be what this amp does,
and SSB actually be within 600-800 watt range.

AND LASTLY, should I worry or just run the thing?"


 >>> I think that's about right....500 watts CW, 800 PEP - as read by a PEP wattmeter - is about what you will see on a good day.

 ....and no, I wouldn't worry about it; just be sure to keep grid current within limits by using enough loading and limit drive from the exciter.


 As Steve indicated, I wouldn't be too concerned about flash-over.

 When running RTTY, the line current requirement is even less than on CW (the manual recommends limiting plate current to 400 ma) which is approx. 6 amperes from a 120 volt line - about half the current of a conventional residential duplex feed, so a stiff 240 volt line shouldn't be a requirement. But for most amplifiers, I would try to dedicate a service for the amplifier, in this case a dedicated 120 volt line that's not powering anything else in the shack or in your the house.


 ...WA1RNE
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WA1RNE
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« Reply #27 on: March 16, 2008, 08:03:16 AM »


 Jeff,

I didn’t imply or address anything from what you read because you didn’t mention or offer any specific advice  about KE4VYN’s issue, other than to say the tubes are all working and “Try it agian and just increase the Load some you will see grid drop”, then some advice from 2 other hams.

So you still have me a bit confused about the purpose of your post.


As for your last observation about the manual and last comment:


“Do not exceed 750mA of plate current during tune-up"

 "Now that tells me that you can go on and adjust it for maximum power out but do not go over .750Ma. "



 >>> I indicated in my last post that this is likely an error which is presented in the manual as a “note” at the bottom right side of page 6. I would not recommend running this amplifier with 750 ma of plate current as doing so will exceed the plate dissipation rating of the tubes, not to mention that the power supply is also likely not rated for CW operation at this power level. One of the dead giveaways is the line fuses; they are rated for 12 amperes each. At 750 ma of plate current,  102 watts of power for the filaments and approx. 10% for losses in the power supply, that’s about 1350 watts drawn from the line or about 11 amperes – not a lot of margin for a 12 ampere line fuse.


“So there my Dear freind did i explain my self ok now Huh? Jeff”


>>> No, you really didn’t.


….WA1RNE
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N3JBH
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Posts: 2358




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« Reply #28 on: March 16, 2008, 10:33:29 AM »

and i doubt i ever will. ok you can have the last word Smiley
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K7GRR
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Posts: 50




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« Reply #29 on: March 17, 2008, 01:40:36 AM »

I own an 811H, couple of comments:

1) 500 watts out on RTTY is way too much.  If you read the fine print, the manual says 1/2 hour continuous carrier (RTTY)is 400 watts.  If you dig further, that's 400 watts *INPUT* per the specs.

2) Also per the manual (and confirmed by me with tech support) you want to tune differently for RTTY, peak at desired power, not max smoke and then back it down.

3) In another thread regarding replacing the 811 tubes with 572 tubes, Ameritron tech support said something along the lines of (can't find the quote) (if I recall correctly) about 240 watts out RTTY with the 811A tubes.

Just a thought.

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