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AMERITRON AL-811 H

M

Mister Heat

Member
Jun 22, 2006
48
1
18
St Croix Valley Minnesota
Local ham operator has one up for grabs locally here. In comparison to other tube amps would this model be a good fit to operate in the 10/12 meter bands. Unit is capable of running at these frequencies, not really designed for AM operation however ?
Ameritron AL-811H
 

'M.H.',
Depends on what he wants for it, and what you plan to drive it with.
Nothing wrong with the AL-811H's if driven correctly and used for SSB or CW. They are not exactly made for AM, will work there, but don't expect much at all, nothing like their usually stated output for SSB/CW. All of the '811' amplifiers are made more for the lower HF bands rather than for 10/11 meters. Very nice on 20 meters, slightly less than adequate on 15 meters though, sort of.
And then it just depends on what he's asking. If it's less than half of the new price, snap it up and re-sell it if nothing else!
The AL-811H uses something between 30 and 100 watts for drive. Both 'ends' of that are sort of 'pushing it'. Especially the 100 watts thingy on AM, I just wouldn't go there at all.
Something else I definitely would not do is 'over-volt' the things. They have a variable input transformer tap, meaning they can be powered from around 100 vac to about 130 vac. One trick is to adjust taps for using 100 vac when the actual input voltage is closer to 120 vac, makes for higher plate voltages. Also makes for more heat build up. Have a friend who's modified AL-811H sort of melted the tank coil's supports. More of a 'U' shape than straight. Luckily he caught things before experiencing the "OH SHIRT!" results. Bad enough on 120 vac, you can also do the same thing (but much easier) on 240 vac. Also one reason why 'lifting the hood' on used amplifiers is a very good thing to do before 'plunking' any money down, and not just on the '811's.
- 'Doc

[It's not the 'H' model but I do have an '811 amplifier. Wouldn't really get rid of it (unless offered some ridiculous amount of money), but don't think I'd get another.]
 
In those '811 amps the tubes are being run at max capability and then some. AM operation is definately NOT reccommened unless you drive it at the low end of it's operational ability.The AL-811 three tuber is good for 600 watts pep so that would equate to only 150 watts dead key on AM and even that will burn up the tubes. I have seen an 811 amp with holes literally burned through the plates because it was run on 80m AM with 150 watts carrier.IMHO a three tube 811 amp is not good for any more than about 75-100 watts dead key or four times that pep if you want the tubes to have any reasonable lifetime.The power supplies are also not designed for AM use either.A lot of folks only think about the tubes for AM service but the power supply requirements are much higher for AM as well.

Ooops....just noticed you said the "H" version. Increase my above figures by about 33%. ;)
 
Remember, too, that if you change the transformer taps, you're also raising the filament voltage, which will quite dramatically decrease the tubes' lifespans.
 
Beetle said:
Remember, too, that if you change the transformer taps, you're also raising the filament voltage, which will quite dramatically decrease the tubes' lifespans.
Click to expand...

Thanks Beetle. That was actually the first thing I thought of but somehow while posting it got lost between the brain and the fingers.That's why I like separate plate and filament transformers.If the 811A's were replaced with 572b's they would yield the same power output but the tubes would last much longer.572B's can simply be dropped into the sockets with no changes to the circuitry.
 
QRN,
Having been there and done that, replacing the '811's with 572Bs will not keep the output the same without increasing the plate voltage. Not a huge difference in output, but definitely measurable using a typical watt meter (not the ears on the other end). You are right about the 572B's lasting almost for ever, since they are being driven quite a bit under their capabilities. Changing filament voltage back to what it ought to be when 'over-volting' an AL-811/AL-811H isn't all that difficult, but it is necessary (shaded of Rick Measures! Or 'Ameritron's techs if you happened to have called them and asked about it.) This was 'way back when' so keep that in mind. They must have had enough calls about that swap, cuz 'Ameritron' came out with their '572 amplifier not long after that.
- 'Doc

(still got those 572's but no idea where they are now.)

Oh, just happened to remember. Running those '572B's "softly" also causes some distortion, 'mushy' sort of thingy. Again, not hugely noticeable, but there.
 
Interesting what you say about the power not staying the same without increasing the plate voltage. I know that for normal operation the 572B's like about 2200 volts but I know two guys that replaced the 811's with 572B's and claim no differance. Perhaps they simply meant no noticable differance on air. :roll: I never thought to ask specifcally what the power output was. :?
 
Let me re-phrase that a little! (Since I didn't say what I meant exactly the way I should have.)
As a simple swap, no changes in plate voltages, there is a slight decrease in output with the 572's. Not a huge difference, but a difference. If you weren't paying particular attention to it you'd probably never know of the swap on the receiving end.
Raising the standard plate voltages very slightly would make that difference go away. But if you're gonna do that, why not just raise it to the 572's 'standard'? That's not exactly all that simple to do though. There are a number of 'other' things that should be done to the stock amplifier(s) to make them compatible with the swap in tubes. If you've got a closet full of 572B's and only one spare 811, I think making that change would be a fairly good idea. If you happen to run across a very good deal on very large quantities of 811's, I think I'd just leave the thing alone.
- 'Doc
 
I agree with you Doc. The 811A's are quite rugged considering their relativly low plate dissapation.It is amazing to see what they will do and tolerate.I personally do not like to see much color on the plates of tubes but most 811A type amps show a lot of dull orange even when run according to manufacturers specs.I'm still trying to get over color of my pair of 4-400's running in modulator service even with no audio applied.The plates start to show orange even in standby.With full audio applied the mods and 4-400 finals get really bright orange. This is in an AM broadcast TX BTW that I am converting to 80m. A fellow b'cast engineer that runs 4-400's as drivers in one of his 10 Kw rigs tells me that his 4-400's usually run with the plates between bright orange and white. :shock: :LOL:
 
QRN said:
I agree with you Doc. The 811A's are quite rugged considering their relativly low plate dissapation.It is amazing to see what they will do and tolerate.I personally do not like to see much color on the plates of tubes but most 811A type amps show a lot of dull orange even when run according to manufacturers specs.I'm still trying to get over color of my pair of 4-400's running in modulator service even with no audio applied.The plates start to show orange even in standby.With full audio applied the mods and 4-400 finals get really bright orange. This is in an AM broadcast TX BTW that I am converting to 80m. A fellow b'cast engineer that runs 4-400's as drivers in one of his 10 Kw rigs tells me that his 4-400's usually run with the plates between bright orange and white. :shock: :LOL:
Click to expand...

--------------------------------------------------------------------------------
Well, sorry to resurrect such an old strand, but this showed up in my search for topics including 4-400 tubes so I thought I'd mention my experience with a pair of 811A tubes from back in High School days (1976).

E.F..Johnson Viking Courier (over)driven by a Browmning One-Eighty amplifier behind an SBE LCBS-8.

LSB & a long "Aaaaauuuuuuuuddddddiiiiiiiiiiiiiiooooooo".

960w pep from 2 811A tubes.

From gray plates to white plates in 3-4 seconds.

Looking back I'm more amazed at the power supply in that old Johnson Courier than I am a pair of 811As providing 480w pep EACH. Any tube will overdrive like crazy, (just before it melts down) but that amp was designed to provide more like 360w.

That old saying, "They sure don't build them like they used to" comes to mind.
 
I wish I had saved the tubes that were in my 811 when I got it, they were fried.
The Plates had holes in them, and I mean "holes", the Glass was discolored, and the Transformer has a "cooked" spot on it were tube next to it was overheating the cover wrap.
He also gave a a spare set of "used" tubes that the plates had been so hot on that the metal had sagged down on them.
I bought the Amp for a song, got me a set of NOS RCA 811A tubes, and it has worked for several years now with out a problem. The deal is DO NOT ABUSE THEM.
These amps will do a great job on SSB, look for about 500/600 watts in that mode, on 10/12 meters. If you plan to run it on AM, (as has been said already)do not key them more than about 100/150 watts(4 tuber) output or you will need a steady supply of tubes.
If you do not push it to the wall when running it , it will do a fine job.....

73
Jeff
 

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