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Author Topic: 811A TUBE FLASHOVER, ARCING OR OTHER EVENT FROM SHORTS? RESULT?  (Read 5461 times)
N6QWP
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« on: March 02, 2017, 06:24:45 PM »

Wondering if anyone with an amplifier that uses 811A's has ever experienced a flashover, arcing or shorting of tube's internal plate, grid or filament and what catastrophic result ensued?

What is the worst that has happened to the amp?  Other than components like tubes, resistors, capacitors and burnt wires, have any resulted in damage to major components like the transformer, power supply board or coils or variable capacitors?

Trying to determine the worst possible scenario from 811A tube failure.

Particularly interested in 30L-1 or AL-811 or AL-811H incidents but any using 811A's of interest.
« Last Edit: March 02, 2017, 06:40:54 PM by N6QWP » Logged
N0SQ
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« Reply #1 on: March 02, 2017, 07:32:45 PM »

Turns out that I lost D16 - the meter protection diode. It shorted. I did lose a variable capacitor also. I didn't realize that D16 was shorted until recently. It probably shorted when the capacitor took a hit.
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W8JX
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« Reply #2 on: March 03, 2017, 02:57:11 AM »

Trying to determine the worst possible scenario from 811A tube failure.

Perhaps you should avoid 811 tubes as a better solution rather than worrying about predicting the damage when they fail. They typical greatly exceed their ratings in AL811 amp and can warp and short out or arc over from reduced clearances from heat damage or loss of vacuum due to heat damage to seals. the 811 is a far lighter duty tube for amp use than many realize.
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VK3BL
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« Reply #3 on: March 03, 2017, 06:37:42 AM »

A search of this forum or even reading the first 3 pages of 811 based threads should be enough to answer this question.

Just in the last week I've covered it in almost every single thread.

Not trying to be rude, but when a bunch of people have covered the same thing over and over in the last week, one has to wonder why the question is still being asked.

To be clear:
-D16 will pop and need replacement almost every time
-The back fuses may blow if the tube arcs hard
-I do not know of a single case of transformer failure.

Please read the other threads.

If you're scared of arcs, just buy RF Parts Taylor series 811As.
« Last Edit: March 03, 2017, 06:55:04 AM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N6QWP
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« Reply #4 on: March 03, 2017, 07:41:57 AM »

This thread was specifically started to elicit responses from users of 811A tubed amps "who have personally experienced any catastrophic" failures or damage resulting from tube failure.

While the many posts that deal with these amps do contain very useful information, I have not seen any postings, so far, that relate to personal "severe" damage from such events.

It was intended to get responses from those hams who are not constant contributors and who might not otherwise share their experiences....but have valuable information relating to this particular issue.  

Owning a 30L-1 myself, I am trying to get "first hand" accounts of such incidents....not philosophical or denigrating comments or pontifications.

From others who have had such experiences, I hope to learn what rare and expensive parts to be on the lookout for, as a preemptive strategy-so as not to suffer possible long downtime in the future.

I feel that others might also benefit from such information-and perhaps like to plan for any eventualities.

That being said, the very useful and knowledgeable responses by those who regularly pass along their expertise and insights are very much appreciated.  Thank you all for the help you provide.  73








« Last Edit: March 03, 2017, 07:57:37 AM by N6QWP » Logged
W1NK
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« Reply #5 on: March 03, 2017, 08:25:54 AM »



-D16 will pop and need replacement almost every time
-The back fuses may blow if the tube arcs hard


These were my experiences back in my AL811 days ... it probably took longer to remove the case screws than it did to make the "repairs".

Frank, W1NK
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K9AXN
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« Reply #6 on: March 03, 2017, 09:05:32 AM »

Frank and Frank,

You're curiosity is a breath of fresh air.  It's what hams and amateur radio hobbyists have done since forever; question what happened, what precipitated the event, how to reduce the risk of reoccurrence, and maybe make it a better radio.  All interesting reading.  Your effort to bring more than the handful that post to the table is overdue.  

I have found the 811 tube and the amplifiers that use it fascinating.  I believe there's an overlooked and untold story surrounding the 811, various designs, expectations, and protection mechanisms for the tube and components.  That said.

W1NK --- Frank, was there any tube damage and if so do you have the tube tubes?     

The following url  https://pa0fri.home.xs4all.nl/Lineairs/AL-811H/AL811H%20modifications.htm? has a close up of an arced 811.  Some of the detail to note:  The shiny patch on the plate indicates it was overheated, The arc was from plate to the center hanger mount for the filament at the bottom of the tube, and the melted glass in the seal area.

The author of that url also provided a protection mod to prevent tube and component damage in the event of a flash or mechanical failure.

BTW, the 30L1 used a little known 1" #30 wire in series with the B+ for overcurrent protection.

Regards Jim  

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W1NK
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« Reply #7 on: March 03, 2017, 10:57:33 AM »


W1NK --- Frank, was there any tube damage and if so do you have the tube tubes?     



Jim:

When the amp blew fuses, the tubes (I no longer have them) showed the tell-tale shiny spot on the plate due to overheating.  This was during my "getting-to-know-you" phase with the amp.  I was likely either not allowing sufficient cool-down time for the tubes when tuning or just plain hammering the amp in contests.  I don't recall any other physical damage to the tube(s).

As far as D16 shorting, I'm not sure what caused it.  I recall it happening twice, though.  One time I actually heard a soft "pop" before the Ip & Ig meters began tracking each other.

Frank, W1NK
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VK3BL
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« Reply #8 on: March 03, 2017, 02:20:02 PM »


As far as D16 shorting, I'm not sure what caused it.  I recall it happening twice, though.  One time I actually heard a soft "pop" before the Ip & Ig meters began tracking each other.

Frank, W1NK

D16 is their basically to 'pop' if ever the HV supply finds its way to the grid.  Sometimes as you've noted, tube arcs / flashovers can be next to inaudible.

D16 is pretty sensitive, but hey better than anything else.  When it dies it shunts HV to ground.  Its actually in "backwards" as a diode as such, so its sole purpose is to breakdown when hit with HV and still conduct.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
VK3BL
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« Reply #9 on: March 03, 2017, 02:32:11 PM »

This thread was specifically started to elicit responses from users of 811A tubed amps "who have personally experienced any catastrophic" failures or damage resulting from tube failure.

While the many posts that deal with these amps do contain very useful information, I have not seen any postings, so far, that relate to personal "severe" damage from such events.

My apology, the title mislead me and it was late here in VK.

Unfortunately, it probably won't really help to ask about 811A catastrophic failures as such, when what you really want to know is what happens when a tube fails in a 30L1.

For example, in the AL-811 series design, what I covered is about it.  Its pretty much bulletproof from the factory.

The 30L1 however is a different design separated by many decades with different and older components.  I would not feel comfortable generalising across two different designs, or even reading the schematic of the 30L1 and trying to predict failure.  My THP HL-1K welded the INPUT relay shut after a tube arc; I sure as heck didn't see that coming after using Tom W8JI designed Ameritrons! Smiley

I believe you would be best served by asking about / searching for and reading "30L1 Problem" or "30L1 Issue". 

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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N0SQ
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« Reply #10 on: March 03, 2017, 04:35:42 PM »

As far as D16 shorting, I'm not sure what caused it.  I recall it happening twice, though.  One time I actually heard a soft "pop" before the Ip & Ig meters began tracking each other.

Last night, I discovered that D16 shorted out but the grid and plate currents did not track each other. The grid current was always 200 mA to get rated output and I never saw a dip. Another effect was that 160 meters acted like it was missing the padding caps (both LOAD and PLATE were 0) - but the caps are there. After replacing D16 everything began giving correct grid and plate current ratings. Even the plate HV reading began reading much closer to 1700 VDC (assuming that the amps meter is somewhat correct - wish I had an HV voltmenter). Hopefully, I won't have any more problems for awhile.
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G3RZP
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« Reply #11 on: March 03, 2017, 05:43:36 PM »

OK, I KNOW I'm going to get flamed.....

I don't believe the 30L1 is a well designed amplifier. Lets look first at the parallel feed plate choke. It's 40 microhenries.  That's an XL of 880ohms on 3.5 MHz. With about 1500 or so volts of B+, that's at least 1200 volts peak or 840 volts RMS across that choke or around just under 1 Amp of current in it. Let's assume Q= 200 ( being generous) R = 44 ohms and power lost in the choke is about 45 watts, give or take. Then there isn't any real further filtering to keep the RF current out of the electrolytics.

There's no neutralisation which RCA recommend, while the capacitive reactance from grid to ground with 220 pF Capacitors is supposed to provide NFB. OK, where are the descriptions and design equations to prove this? Now I don't always agree with W8JI, but in this case, I am very dubious, and it is noted in several quarters that the 30L1 is  not terribly stable on the higher bands into an antenna that isn't 1 to nearly 1.

I'd love to see the math that proves the NFB: it's not in 'Single Sideband Fundamentals and Circuits' by Pappenfus, Bruene and Schoenike.

Plus the wiring in the earlier handbooks for 220/230 volt operation is basically lethal...
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N6QWP
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« Reply #12 on: March 03, 2017, 06:33:50 PM »

Your expertise is obviously above reproach on theoretical electronics....and I am hardly qualified to even offer a differing opinion.  I would, however, point out that there were over 17,000 30L-1's produced-and while I have no idea how many are still around, they still have a loyal following and still command a good price by hoards of hams.  

While they certainly have their limitations and a few problems, many thousands are still in service and giving praiseworthy service to most of those who feel that are lucky enough to possess one.

There are, indeed, newer and more modern designs of 811A amps out there, but IMHO, none can match the quality of construction and parts of these venerable workhorses.

If, seeking a low cost, lower power amp of unequaled quality-that uses 811A tubes, with a few updates, these 30L-1's offer an addition that adds class to any shack.....Plus, they exude that old style Collins aura.

,




« Last Edit: March 03, 2017, 06:56:29 PM by N6QWP » Logged
VK3BL
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« Reply #13 on: March 03, 2017, 07:19:54 PM »

OK, I KNOW I'm going to get flamed.....

I don't believe the 30L1 is a well designed amplifier. Lets look first at the parallel feed plate choke. It's 40 microhenries.  That's an XL of 880ohms on 3.5 MHz. With about 1500 or so volts of B+, that's at least 1200 volts peak or 840 volts RMS across that choke or around just under 1 Amp of current in it. Let's assume Q= 200 ( being generous) R = 44 ohms and power lost in the choke is about 45 watts, give or take. Then there isn't any real further filtering to keep the RF current out of the electrolytics.

There's no neutralisation which RCA recommend, while the capacitive reactance from grid to ground with 220 pF Capacitors is supposed to provide NFB. OK, where are the descriptions and design equations to prove this? Now I don't always agree with W8JI, but in this case, I am very dubious, and it is noted in several quarters that the 30L1 is  not terribly stable on the higher bands into an antenna that isn't 1 to nearly 1.

I'd love to see the math that proves the NFB: it's not in 'Single Sideband Fundamentals and Circuits' by Pappenfus, Bruene and Schoenike.

Plus the wiring in the earlier handbooks for 220/230 volt operation is basically lethal...

My silence should be deafening.  The above post is bang on the money.

Nothing wrong with wanting to use vintage gear, but it is worth bearing in mind things have come along way.  When was the last time anyone built a new windom and ran a single line feeder into their shack, for example Wink

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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
K9AXN
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« Reply #14 on: March 04, 2017, 05:43:28 PM »

OK, I KNOW I'm going to get flamed.....

Only if you go to one of those Japanese restaurants where the chef builds a fire in a mountain made with an onion filled with oil and alcohol.

I don't believe the 30L1 is a well designed amplifier. Lets look first at the parallel feed plate choke. It's 40 microhenries.  That's an XL of 880ohms on 3.5 MHz. With about 1500 or so volts of B+, that's at least 1200 volts peak or 840 volts RMS across that choke or around just under 1 Amp of current in it. Let's assume Q= 200 ( being generous) R = 44 ohms and power lost in the choke is about 45 watts, give or take. Then there isn't any real further filtering to keep the RF current out of the electrolytics.

Not so, C16, L13, and C34 represent a low pass filter cutoff around 2Mc.    Question for you.  How much AC current will the 4 tubes deliver to the output tuned circuit at max out and how much time do you spend with the key down?   

There's no neutralisation which RCA recommend

The added negative feedback described next, reduces the gain of the amplifier also reducing the requirement for neutralizing.  NOTE:  Even though I don't believe the 30L1 must be neutralized, I advocate neutralization if done properly for linearity and IMD.


while the capacitive reactance from grid to ground with 220 pF Capacitors is supposed to provide NFB. OK, where are the descriptions and design equations to prove this? Now I don't always agree with W8JI, but in this case, I am very dubious,

Look at page 212 Fig 14-1 the genesis of the 30L1.  Note the three note marks (4) at the plate of the 811A.  The first represents the plate to grid capacity and the second, the 200pf capacitor added between the grid and ground.  The values are the same as used in the 30S1 which represent the NFB bridge ratio of 1/40.  The 30S1 bridge was copied into the 30L1. The 30S1 adding a 5pf capacitor from plate to control grid bypassing the screen whereas the 30L1 uses inter electrode plate to grid capacity for the upper bridge capacitor.



and it is noted in several quarters that the 30L1 is  not terribly stable on the higher bands into an antenna that isn't 1 to nearly 1.

The manual says to keep the SWR below 2/1.  The only place I've read any such thing is on the JI web site and he has an agenda.  Any reputable sources you can cite?  See CCA Signal Q4 2013 for more testing information.  There is information most good some marginal but most other sources are campfire gossip.


I'd love to see the math that proves the NFB: it's not in 'Single Sideband Fundamentals and Circuits' by Pappenfus, Bruene and Schoenike.

It is described for the 30S1 on P.214 14-2 in that book and a deeper description can be found in CCA Signal Q1 2015 and many other locations in the Collins archives.  Vomiting math rather than accepting the explanation written by the designer, an  outstanding RF engineer, on a list populated by a diverse intellectual base is self serving.  If you can't wrap words around the concept you simply don't understand it.  However a bridge with a ratio of 1/40 cannot be to complicated to reconcile.  Also, a simple test which has been done is to measure the drive necessary to max out with the capacitor to ground then go with direct grid to ground and re-measure.   You will find a 30+% reduction in drive necessary with the grids grounded.

Last, You have a choice to make with for the inductance of the grid lead in the tube.  It is approximately 40nH to 45nH.  You can ground the grid lead with a 1" flat silver plate and when your finished the grid lead will still be 40nH to 45nH inductive or you can implement the 200pf capacitor to ground which will change the tube inductance to capacitive reactance.  Regardless, it will be less inductive than a directly grounded grid.  Would you prefer more or less inductance in a grid lead --- you decide.
     


Plus the wiring in the earlier handbooks for 220/230 volt operation is basically lethal...

Read the mods and current material then comment.


For me, everything that needs saying has been said ---- won't be driving this road any longer.  Make choices that make you happy with whatever radio is your favorite.  Nobody has ugly babies.

Have a great day  Regards Jim


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