AL-811HD as AM Amplifier

[W1KSZ]

I am thinking about moving out the Valiant and getting a Ranger.
Much easier to move around, but I still want the power.

So, I thought the Ranger driving the Ameritron AL-811HD might
fill the bill. The -HD variant has 4 572B's instead of 811A's.

I would run it at about 250-300 Watts out.

Any opinions on my next new mad scheme ??

Thanks, Dick, W1KSZ

[Pete, WA2CWA]

Maximum drive power permissible: 85 watts
Typical drive for rated output: 65 watts

Overall the Ranger/Ameritron might spend much less time on the work bench then the Valiant.

[W2VW]

I'd consider a pre-owned larger AMplifier. That machine is shown as an 800 watt P.E.P. output unit. Figure less than 1/4 of that available for carrier.

It has plenty of plate dissipation but the power supply is the limiting factor.

[AB2EZ]

Dick

AM is very hard on linear amplifiers... even when they are properly loaded.

At carrier, the efficiency will be around 33% (maybe less).

If the RF output is 300W at carrier, then the tubes will be dissipating around 600W (maybe more) throughout each transmission. This corresponds to a total of 900W of electrical input power.

On 100% modulation peaks, the electrical input power will double to 1800W, but the RF output power will quadruple to 1200W. So the tubes will also be dissipating 600W on modulation peaks.

The tubes will get very hot during each transmission, and then cool down when you stop transmitting. The heating and cooling will cause a lot of mechanical stress on the tubes.

You may find that you have to run the linear at a carrier level that is much less than you think.

I ran my 3-500Z linear at 100W of RF output power at carrier level (which corresponded to an RF input power of around 5W at carrier level) even though it could produce 800W of peak RF output power on CW or SSB (manufacturer's rating). With the input signal unmodulated, I (iteratively) adjusted the RF input signal level, and then optimized the loading... to produce 500W of RF output power. Then, without changing the loading, I reduced the unmodulated RF input signal level until the RF output power was 100W. This results in maximum output stage efficiency, while still providing some headroom above 100% modulation (400W of RF output power).

Even so, the tube had a tendency to form a crack in the glass near the plate cap (even with an extra cooling fan and a large heat dissipating plate cap).

Stu

[K1JJ]

Hi Dick,

Here's a few more AM rig suggestions to consider that you will never outgrow:


1) Look around for a well-built homebrew GG 4-1000A linear amplifier. They are around and can be had for a good price. Some of the old timers are selling out.  Depending on HV and air, good for about 400 watts carrier, 2KW pep.

2)  Look around for a homebrew pair of 813s modulated by a pair.  Or build your own:
 http://www.amwindow.org/tech/htm/813/813.htm   Easy 500 w carrier

3) Build or find a used class E solid state rig. At this point in time, there are some guys wishing to build bigger and may sell their existing E-rigs to defray the cost.   300 w to ?  depending on number of pills.

* In general, build or buy somewhat bigger than you need. Run it at 1/2 power for cleanliness and longevity.  Just like any hobby, we all tend to want something bigger and better later on.  Might as well do it now.

T

[K9DXL]

I run my Heath DX-60 with my AL-811H for a worthwhile power increase of about 200 W out.  A carrier control rig is a bit easier on a medium duty amp than a plate modulated transmitter with its higher resting carrier output.  WC3K (SK) wrote some articles for Electric Radio about this combination.

[W1KSZ]

Well, that idea went over well !! Guess I'll move the Amp along and stick
with the Valiant, for now.

Also, the idea of some monstrous hunk of iron does not appeal to me.


Thanks for all the replies,

73, Dick, W1KSZ

[Pete, WA2CWA]

I've run my SB-200 (pair of 572B's) on AM and SSB since the mid 90's. Still have the original tubes (installed in 1969), caps, and just about everything else. I generally run it around 100 to 110 watts carrier. It hasn't died on me yet. My Valiant sits at the end of my workbench where its been for the last 10 years. Maybe one of these days I'll repair it or maybe just use it as a fireworks display.

[kb3ouk]

If you are looking at purchasing a new amp, I would look at one with at least a pair of 3-500Zs or better. The AL-800F with a single 3CX800A7 sounds like a good deal. 1200 watts PEP capable, it should do well running about 250 watts of carrier, just be careful with the tube and it should last a while. From what I read, it supposedly has same power supply as the AL-800H, which runs a pair of the same tube. I have no personal experience with that amp, but I can tell you that I highly doubt that the AL-811HD that you originally mentioned would do over 120-150 watts, which only is a little over 3dB gain from the Ranger, so really not worth it. I have an old Hunter amp that runs a quad of 572Bs, and even with the beefy power supply in that thing, the tubes seemed to run out of steam when going over 150 watts.

[WB5IRI]

Seriously, if you are going to run a linear designed for SSB on AM, it ought to be one of the really beefy ones -- like an Alpha, for instance. They used to (and still do) advertise putting a brick on the key and walking away, so they will take the mode and the power, as long as you are reasonable. But then you are right back in the huge heavy boat anchor class you are seeking to escape. Class E might be a way -- been thinking about that for awhile myself.

And all you guys wanting to get rid of your Valiants, I'll take 'em off your hands. Always looking for a source for spare parts! ;>)

Doug

[W1RKW]

I say go for it.   Just run it. Be cautious.  Get on AM and have fun.  I've run a quad of sweep tubes on AM without trouble. As Clint says, man's got to know his limitations.

[w1vtp]

Assuming 4 X 811A's  That's a total dissipation of around 250 watt.  I wouldn't run much more than 100 watts of carrier. As far as peak env.. power.  At 100 watts power and 125% modulation posi.. peak = a tad over 500 watts PEP.  Probably safe to run it at that level

[Pete, WA2CWA]

Assuming 4 X 811A's  That's a total dissipation of around 250 watt.  I wouldn't run much more than 100 watts of carrier. As far as peak env.. power.  At 100 watts power and 125% modulation posi.. peak = a tad over 500 watts PEP.  Probably safe to run it at that level

He said in the first post:  "The -HD variant has 4 572B's instead of 811A's."

[ka4koe]

Pete

The Valiant statement had a distinct ring of truth to it.

PAN

[KB2WIG]

"  You've got to ask yourself one question: 'Do I feel lucky?  "


klc

[kb3ouk]

Assuming 4 X 811A's  That's a total dissipation of around 250 watt.  I wouldn't run much more than 100 watts of carrier. As far as peak env.. power.  At 100 watts power and 125% modulation posi.. peak = a tad over 500 watts PEP.  Probably safe to run it at that level

He said in the first post:  "The -HD variant has 4 572B's instead of 811A's."

But probably has the same power supply as the 811A version, so you would still be limited there.

[W1KSZ]

Au contraire mon ami ....

I did my due diligence and checked the manuals for both versions,
AL-811H with 811A'a and AL-811HD with 572B's.

Both Power Xfmrs have the same MFJ Part Number. Makes sense,
why stock two versions when the difference is probably minor
in terms of manufacturing cost.

In any case, I have shelved the idea. Anyone want an Amp ??

73, Dick, W1KSZ

[K1JJ]

It is quoted in the Official AM Handbook somewhere: "When all the searching, crap-outs, trials and tribulations and "valiant" cruises thru hell are finally over, all good AMers build a class e rig (or buy a Flex) and go to heaven."  

[KA2DZT]

It is quoted in the Official AM Handbook somewhere: "When all the searching, crap-outs, trials and tribulations and "valiant" cruises thru hell are finally over, all good AMers finally build a class e rig and go to heaven."  

I just got back from heaven (nice place to visit) and I still wouldn't build a class E rig.  Too many easy failures for me.

Tom, what happened to your class E rig??  Probably something bad that you're trying to forget.

Fred

[KB2WIG]

There's always the DX 60 screne mod / amp method of am.....



klc

[W1KSZ]

OK, you have gotten my interest up.

Anyone have any links to a Class E Amp that can be built ??
Not one of these pie-in-the-sky articles I see in some magazine,
but something with some reality to it.

Something around 500 Watts for 160/80/40 would be nice.

73, Dick, W1KSZ

[Pete, WA2CWA]

This will get you started:
http://www.classeradio.com/
Note that these rigs only glow when you burn the MOSFET's up!

[K1JJ]

Tom, what happened to your class E rig??  Probably something bad that you're trying to forget.
Fred

Fred,

The link below is similar to the 24 pill class E rig design I built 4 years ago. It ran fine until I stuffed some towels around the ferrite cores to quiet them down from talk-back.  Evidently they caused heat to take out some transorbs.  Bill/ W1LLY now has the RF module, modulator, PDM filter and shut down board - and should have it on the air in the future once he adds the missing parts.

To be honest, it became boring to run because it was so reliable, like an appliance.  I wanted more action, so built Fabio II. Isn't that a hoot?

http://www.classeradio.com/24_fet.htm


Dick,

Talk with the guys on 3873 at night about class E. They will help you make sense of the website. There are kit boards and parts available for everything except the RF module and PDM filter, which you can make yourself.  The whole project is somewhat more complicated than building a Heathkit.  The rig produces great audio at very high efficiency. They can be bandswitched with relays.   And, you can run them in the summertime!

T

[W2VW]

I just got back from heaven (nice place to visit) and I still wouldn't build a class E rig. 

Fred

You would if they used more iron core transformers.

[K1JJ]

OK, you have gotten my interest up.

Anyone have any links to a Class E Amp that can be built ??
Not one of these pie-in-the-sky articles I see in some magazine,
but something with some reality to it.

Something around 500 Watts for 160/80/40 would be nice.

73, Dick, W1KSZ

Dick,

Here's a thread on the AMfone BB about building Rico Suave, a 24 pill class E rig.  It will show you some of the things you will need to address to successfully build one.  (It now has over 26,000 hits, probably due to Google searches)


You don't have to do 24 pills, of course.    Six pills would be plenty - and simpler.  It's about 50 watts per MOSFET.

http://amfone.net/Amforum/index.php?topic=23354.0

T