So you're saying that for a plate current of 450mA the grid current should be 300mA?? :blink: 450mA/300mA =3/2 Say good bye to those tubes.
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AL-811 Problem
- Thread starter W1MSG
- Start date
So you're saying that for a plate current of 450mA the grid current should be 300mA?? :blink: 450mA/300mA =3/2 Say good bye to those tubes.
Toll_Free
Well-Known Member
Captain KayDub....
I do have to restate what I was saying earlier, I had the actual order of the elements in the tube wrong...
The 3/2 law is the ratio of grid VOLTAGE to plate current. In a LINEAR amplifier.
Off in left field earlier....
BUT, take a look at a properly running grounded grid amp with decent sized grids in it, and see what you get for grid current / plate current...
When I pull 100 mils of grid current, I pull about .4-.5 A of plate current in my 3-500Z amp. I do run lower voltage, though. Keeping the tube in the most linear region.
Sorry for the confusion. I think one of the problems also is that the 8xx and 57x, as well as other 'vintage' tubes is that they lack the grid necessary (actually, it's more the physical connections to the outside world, they can't conduct the heat away fast enough via the single or sometimes dual pins on RXer type sockets, the spring tension is never good enough, etc.) to be able to 'steady state' the amplifier long enough to get real readings....
A 3CX3000, 4CX5000, etc.... Even the 4-1000 in GG mode all have enough Gdiss that you can steady state them and watch the meters. Try it with the AL811, and you brought up the end results
Especially with the Chinese tubes, I've seen the older RCA and CETRON tubes stand up a little better to CCS modes and lid operators.
--Toll_Free
For those that want to learn more about the 3/2 law, check Eimac's Care and Feeding...
http://www.cpii.com/docs/related/22/C&F6Web.pdf
I do have to restate what I was saying earlier, I had the actual order of the elements in the tube wrong...
The 3/2 law is the ratio of grid VOLTAGE to plate current. In a LINEAR amplifier.
Off in left field earlier....
BUT, take a look at a properly running grounded grid amp with decent sized grids in it, and see what you get for grid current / plate current...
When I pull 100 mils of grid current, I pull about .4-.5 A of plate current in my 3-500Z amp. I do run lower voltage, though. Keeping the tube in the most linear region.
Sorry for the confusion. I think one of the problems also is that the 8xx and 57x, as well as other 'vintage' tubes is that they lack the grid necessary (actually, it's more the physical connections to the outside world, they can't conduct the heat away fast enough via the single or sometimes dual pins on RXer type sockets, the spring tension is never good enough, etc.) to be able to 'steady state' the amplifier long enough to get real readings....
A 3CX3000, 4CX5000, etc.... Even the 4-1000 in GG mode all have enough Gdiss that you can steady state them and watch the meters. Try it with the AL811, and you brought up the end results
Especially with the Chinese tubes, I've seen the older RCA and CETRON tubes stand up a little better to CCS modes and lid operators.--Toll_Free
For those that want to learn more about the 3/2 law, check Eimac's Care and Feeding...
http://www.cpii.com/docs/related/22/C&F6Web.pdf
Ok so am I totally screwed up by thinking 150mA Grid should be 450mA Plate ?? But that would make it 3/3. I suck at Math ..
I get confused easily, but this is also what Ameritron says is the max for each on my 811 and my numbers are just a little lower than those.
I get confused easily, but this is also what Ameritron says is the max for each on my 811 and my numbers are just a little lower than those.
I tune just like the ameritron youtube video and everything works perfect. I get close to 600 ssb. I think you should do the same. If you think to much about it and ask how you will just get mixed up.
AP
AP
not being "agressive", but , i do agree, you really do suck @ math
that would be :450/150 = 3/1the point is really about "over' VS "under "coupling. after you have the amp properly loaded (tuned to the dip), just bump the load control a little more to the right (clockwise).
NEVER retune an amp with lower drive for lower output power. just reduce drive after it is properly loaded. this does not apply if you are doing heavy duty cycle operations (RTTY, SSTV, ect)
err,
you give a "law" that is a ratio of grid voltage to plate current,............ then you cite a ratio of grid current to plate current.
perhaps it wouldn't be so confusing (to some) if you didn't flip flop between grid CURRENT and grid VOLTAGE.
... and , yes, i do know how to talk "apples and oranges" too
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Toll_Free
Well-Known Member
err,
you give a "law" that is a ratio of grid voltage to plate current,............ then you cite a ratio of grid current to plate current.
perhaps it wouldn't be so confusing (to some) if you didn't flip flop between grid CURRENT and grid VOLTAGE.
... and , yes, i do know how to talk "apples and oranges" too
1. I was posting a correction. I had misquoted the actual "theorum", went and checked it, and then posted a correction.
2. The numbers I quoted about my 3-500Z amplifier where so the person I was responding to could see the numbers actually DID make sense..... IE, 130 mils / .400 A. Sorry if it was confusing.
Not too many people have an actual grid VOLTAGE meter in their GROUNDED GRID amplifiers, making it harder to explain when you have to interpolate the grid voltage by knowing the input Z and grid current.
Now, how many people here have built a grid driven triode amplifier before?
--Toll_Free
Best advise I have seen.. This is exactly what I do and will continue to do.
I do suck at math but that was a slip of the keyboard, should have been 3/1.
Toll_Free
Well-Known Member
BINGO!!!, exactly my point
... and i would "guess" ,... at least two
I'll bite. How do you measure grid VOLTAGE in a grounded grid amp? Interpolating from Cathode current, etc?
I'm in the process of building a water cooled 3CX30K, but it's a VERY low Mu tube.... Meaning it has to be grid driven... AND it's a 'bolt in grid' tube, with flying leads for the fils.
My plan on it was to mount the grid via a piece of teflon, etc. as an insulator. I'd actually need two, I think. Measuring grid voltage here will be easy.... The grid is lifted.
Just a little more wood for the fire, this isnt the only post I have found about the 811 vs 572 tubes in the AL-811 amp. Ameritron also verified this and said if I change to 572b tubes it would void my Warranty...
Here is a quote from another web site, just one of many I found on the Tube Wars ****
******************************************************************
Great amplifier - 600-700 pep 811a tubes are cheap and plentiful (China has been making them for decades)
Now, free advise!
Do not swap to 572b's. Why? No need - no more power.
Also, not enough plate voltage for them, so they will alwways be mis-tuned. Another reason? Sure. Getter. Will they reach a high enough temp running low to keep air out? Probably not!
More, sure. The 811 circuit has the control grid grounded; if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) IS gonna draw more current than it should and it's gonna draw current when it should not! Look at a schemetic of a Yaesu FL-2100 - or a SB200 Heathkit - or better yet, a schemetic for an AL-572 or the AL-811HD with factory 572b tubes. Circuit is different.
Of course, if you don't mind replacing the 572b regurarly, go fo it! Be sure to buy 2 sets at a time, because they won't last!
Keep those 811 amps with their 811a tubes, they were made fo reach other!
******************************************************************
Hmmmmm seems there are two schools of thought, but I am happy with my new 811A's and my Warranty is still in tact for another 9 months.
Soop: :bdh:
Here is a quote from another web site, just one of many I found on the Tube Wars ****
******************************************************************
Great amplifier - 600-700 pep 811a tubes are cheap and plentiful (China has been making them for decades)
Now, free advise!
Do not swap to 572b's. Why? No need - no more power.
Also, not enough plate voltage for them, so they will alwways be mis-tuned. Another reason? Sure. Getter. Will they reach a high enough temp running low to keep air out? Probably not!
More, sure. The 811 circuit has the control grid grounded; if a 572B tube is put in that circuit without the proper modifications done for the grid leak resistors then that tube (the 572B) IS gonna draw more current than it should and it's gonna draw current when it should not! Look at a schemetic of a Yaesu FL-2100 - or a SB200 Heathkit - or better yet, a schemetic for an AL-572 or the AL-811HD with factory 572b tubes. Circuit is different.
Of course, if you don't mind replacing the 572b regurarly, go fo it! Be sure to buy 2 sets at a time, because they won't last!
Keep those 811 amps with their 811a tubes, they were made fo reach other!
******************************************************************
Hmmmmm seems there are two schools of thought, but I am happy with my new 811A's and my Warranty is still in tact for another 9 months.
So
op: :bdh:Toll_Free
Well-Known Member
Just a little more wood for the fire, this isnt the only post I have found about the 811 vs 572 tubes in the AL-811 amp. Ameritron also verified this and said if I change to 572b tubes it would void my Warranty...
Here is a quote from another web site, just one of many I found on the Tube Wars ****
******************************************************************
SNIP
******************************************************************
Hmmmmm seems there are two schools of thought, but I am happy with my new 811A's and my Warranty is still in tact for another 9 months.
So
They really told you that?
WHEN THEY MARKET THE AL811HD?
Guess I'll have to dl a schematic and see if their are any other things they've done to the "572"'ed version of the AL811H....
Thanks for the info from Ameritron, tho... Won't recommend anyone to change them out again until I compare schematics, etc....
I could possibly see a nuetralization issue, but.... In all the amps I've converted (I won't SELL an 811A anymore) I've never had a problem...
All these NEW technologies!
--Toll_Free
Tried to download the 572 version of the 811 amp manual, no dice.
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Well last week I did a job for a friend that brought in some extra money so I bought a set of new Svetlana 572B tubes fromK5SVC.
He has an e-bay store and I got 3 tubes for $165. They came in this morning and are definitely a plug and play replacement for the 811A's. So much for everything you read on the internet. I no longer care about the warranty after my tube fiasco so I figured if the 572B's are a lot more durable and I have some windfall funds why not get them.
Plugged them in and they tune up in almost the same positions as the 811A's and it feels like less heat coming from the vent on the side of the amp.
They tune up a bit better on 10m than the cheapo Chinese 811's I bought.
Anyway, I have a 1 year warranty on the tubes and reliability and durability is what I want so I just dropped the cash. So hopefully my tube buying days are all over
He has an e-bay store and I got 3 tubes for $165. They came in this morning and are definitely a plug and play replacement for the 811A's. So much for everything you read on the internet. I no longer care about the warranty after my tube fiasco so I figured if the 572B's are a lot more durable and I have some windfall funds why not get them.
Plugged them in and they tune up in almost the same positions as the 811A's and it feels like less heat coming from the vent on the side of the amp.
They tune up a bit better on 10m than the cheapo Chinese 811's I bought.
Anyway, I have a 1 year warranty on the tubes and reliability and durability is what I want so I just dropped the cash. So hopefully my tube buying days are all over