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AL-811 Problem

Well I never said I know better, nor have I corrected anyone. Did you ever consider I might not be able to afford the 572's right now. The decision I made is good for me and thats it.

You seem to have taken offense that I didnt follow your advise.
 
Last edited:
Typical for this week forsure!!! 3rd spat Ive seen in 2 days :eek:

On a serious note its all good you guys everyone is gonna have an opinion and theres always disagreement but in the end its what a person wants is going to be the end result.
 
Ok, the Chinese 811A's came in today and I replaced all the tubes with this matched set.
I noticed a difference when tuning it up, the Plate Current seems to be much lower than it was before and I am using less drive for the same results.

The manual said not to exceed 450mA on the Plate Current and 150mA on the Grid Current. I get to the 150mA on the Grid with about 400mA on the Plate Current, and I am driving it with a bit less drive than I was before.

So does it sound like I am in good shape now, I also have 3 extra tubes in case I have any further issues.

Thanks

Craig
 
Ah - Hmmm....
And just in case you can't find a convenient place to store those extra tubes, I would be happy to store them for you!
- 'Doc

(that's not gonna work, is it?)
 
W5LZ said:
Ah - Hmmm....
And just in case you can't find a convenient place to store those extra tubes, I would be happy to store them for you!
- 'Doc

(that's not gonna work, is it?)
Click to expand...

I think I can find a safe place for them, but thanks for the offer :D
 
You're not too far off... Maybe need a bit more tuning (loading) to get the desired results.

Do yourself a favor (and this goes for everyone running a linear that has grid and plate current meters) and read up on the "3/2 power law" or "3/2 ratio". It will explain what, in a grounded grid amplifier, you actually want to SEE on your meters, and what it means when you don't see what you're 'SPOSED to.


--Toll_Free
 
W5LZ said:
And what/where is that "3/2 power law" or "3/2 ratio" explained?
- 'Doc
Click to expand...

I did a google search but didnt find much except some generic explainations that really didnt talk about radio stuff.

I just watched a couple of videos on Youtube, they were both for the 811H so the maximum voltages are different, I expect that if I stay below the Max recommended in the manual I should be Ok. I am guessing my Tube failure was just a bad tube and not user induced ( at least I hope not ) ..
The new tubes are staying well below the max plate current and I am keeping the grid current under the max recommended of 150mA. I did get a response from Ameritron and they are going to send me a replacement tube since the amp is less than 3 months old. They also said that every once in a while they do get some bad tubes from the manufacturer that fail realatively quick, what ever thats suppose to mean.

Anyway, the amp is back working great and I am getting some good signal reports so I am happy.
 
W5LZ said:
And what/where is that "3/2 power law" or "3/2 ratio" explained?
- 'Doc
Click to expand...

Your guru Rich has explained it many times.

When a Grounded Grid amplifier is amplifying as a 'linear device', the plate current will be 3/2 as a ratio of the grid current.


Maybe this should go under the "how to tune a tube amp"..... Not many people, ham's or CBers can actually load an amplifier up to the prescribed values. Most tune for max smoke, which usually will get you in the right area.

--Toll_Free
 
W5LZ said:
And what/where is that "3/2 power law" or "3/2 ratio" explained?
- 'Doc
Click to expand...


I forget exactly what it entails but it has to do with grid and plate current in an amp. I believe it was something Rich Measures,AG6K, came up with. Either that or I am completely delusional tonight. :blink:
 
Toll_Free said:
Your guru Rich has explained it many times.

When a Grounded Grid amplifier is amplifying as a 'linear device', the plate current will be 3/2 as a ratio of the grid current.


Maybe this should go under the "how to tune a tube amp"..... Not many people, ham's or CBers can actually load an amplifier up to the prescribed values. Most tune for max smoke, which usually will get you in the right area.

--Toll_Free
Click to expand...

Ok makes sense now, and if my math is correct I am right in the ball park, at least I'm not just stuck in left field or worse the parking lot.

My previous tuning numbers were definately off, I still kept them under the max but the Plate was always higher than it is now, my guess is the tube was weak to begin with and finally just shorted, that was throwing all my numbers off.

Learning more and more everyday, I sometimes wish I had chosen a technical field in the Army, but being a trigger puller is way more fun.
 
I tune my AL-811 for max output and then back the drive down to get it where I want the power out and it works great. I bought it used with the original tubes and don't know how old the tubes are but they are lasting very well and I used my amp often.

W1med, you have a great amp there and it does make a difference of a contact or not and if it is tuned correct you will get great reports.

AP
 

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