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Author Topic: Ameritron AL-811H amplifier  (Read 1177 times)
KC4KGU
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« on: January 19, 2002, 04:34:03 AM »

I recently purchased an ameritron AL-811H amplifier.  I am driving the amp with a kenwood ts-2000.  When I tune up, the MFJ-989C shows absolutely zero SWR but, I can't manage to get more than about 500w out of the 811h according to the peak meter on the MFJ-989C.  Since this is somewhere close to the rated SSB output of the 3-hole version of the AL-811, I wonder if I got a bad tube in a brand new amplifier?

Here's what I'm seeing tuning up with CW:

Input power: 50w
Freq: 3.875

Load: 5
Plate: 5.25
Plate Voltage: Just under 1600v
Plate Current: 675mA
Grid Current: 185mA

SWR: needle doesn't move off of zero.
Forward power: 500w

In SSB, I rarely see the peak meter over 400w after tuning for max power in CW.

My question: Is the normal for the 811H or is it a bit soft as I expect?

Many thanks in advance for any help.

73 de kc4kgu
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N8FVJ
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« Reply #1 on: January 19, 2002, 04:49:12 AM »

I do not have my AL-811H anymore, but I needed 80 watts drive to get 750 Watts PEP out. I also remember  about 200 millamps higher plate current over your listed measurement.
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KC4KGU
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« Reply #2 on: January 19, 2002, 05:05:07 AM »

How did you measure your plate current?  The meter only reads up to 750mA.  I can't drive much more into the AL-811H without pegging both the plate current and grid current meters.  50 watts drives them both to near full scale.

73 de kc4kgu
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N8FVJ
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« Reply #3 on: January 19, 2002, 08:19:48 AM »

My plate current meter had a 1 amp scale. I bought it used, and the amp did have some internal changes per previous owner. He stated the amp did not load right on 15 meters before the mods. He did not state the amp had any changes to increase power. My MFJ 986 tuner with internal meter showed about 750 watts out on the 'peak' reading scale while transmitting 75 meter SSB.
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N5TML
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« Reply #4 on: January 19, 2002, 10:23:40 AM »

i wouldnt trust the meter on the amp. they all seem to be different on most of them i see. do the math  1600 x .675 =1080 input  and assuming 60 percent efficiency that would be 648 watts out.   7 3  
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KB9UMT
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« Reply #5 on: January 19, 2002, 11:25:08 AM »

Hello:

Had an 811H and it was a great amp for the money!  Putting all the meters aside (and I sure would not believe the MFJ on SSB) what is your increase to a receiving station??  Do they indicate audio increase..or maybe a couple S units of meter increase??  

de kb9umt Don
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KG6AMW
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« Reply #6 on: January 19, 2002, 11:42:33 AM »

I wouldn't trust meter on the MFJ tuner to accurately measure peak readings.  Since the amp is used, you really don't know the quality of the tubes.  Maybe, that's all they can put out.  Doesn't the 811 put out about 400 watts continuous and 600 on the peaks with SSB.  Therefore, the 811h should put out 600 watts continuous and 800 on the peaks.
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KG6AMW
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« Reply #7 on: January 19, 2002, 11:51:04 AM »

Just noticed you said new.  Forget my comments regarding unknown quality of tubes.
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NG3J
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« Reply #8 on: January 19, 2002, 11:55:23 AM »

I ran into a similiar situation and here's what I've determined.

I also run an Ameritron AL811H and USE to have a MFJ 989c. I purchased the amp a couple of months ago along with the 989c. I read the reviews for the 989 on eham and found that 90 percent of them are NOT favorable towards the tuner. One of the complaints was that the watt meter was far from accurate. I found this to be the case with mine but not as severe. There were a few other problems with the tuner so I ended up returning it for a full refund and purchased a Palstar AT1500CV (costs about $70 more) which is like night and day compared to the 989c. Now that I have a quality tuner, I hopefully can answer your question.

When I tune the amp, for the most part (depending on the band), I get about 500-600 watts CW tone with 50 watts drive. On 160m (the 989c had big time problems tuning the amp on that band), I'm getting close to 800 watts CW with both plate and grid current at acceptable levels! Remember,watch your plate and grid current. Do not exceed 750ma plate and 200ma grid. Once I tuned up on a particular band with a CW tone output of say 500 watts (50 watts drive), I would switch over to SSB and crank the exciter power up to almost 100 watts. On SSB, there is less of a draw on plate and grid and therefore you can crank up the input drive power to 80-100 watts. On the Palstar tuner, I do not have an average PEP indicator like the 989c does. But on peak swings when talking, I see it up around 700 or so. If I threw a watt meter that calculates average PEP, I'm sure I'd see it hovering around 700-800 watts consistantly.

Here's something you may want to think about also. I've read in many reviews of the 811H that if you replace the 811A tubes with Svetlana 572B's, the amp would run much cooler with some seeing a 100-150 watts more on PEP. The downside to this is that the tubes are not cheap. I believe the total cost to change over to the 572B's is around $300-$400. Don't quote me on this, but that's a ball park figure that I've heard. I'll probably switch over to the 572B's but only after I've worked the 811A's to it's life expectancy.

Hope this helps. Any questions, don't hesitate to ask!

- Fred NG3J
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KC5NIS
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« Reply #9 on: January 19, 2002, 09:31:15 PM »

If one of the tubes was bad you would see a mismatch on the input of the amp and some abnormal plate and load settings.  The amp does need more than 50 watts to reach full output.  Don't increase your drive after tuning the amp.  Lowering your drive is ok after tuning but never increase the drive over the level it was tuned at.  Raising your drive to 100w on ssb will overdrive and detune the amp.  The plate and grid meters read average current, not peak, so switching to ssb will cause the meters to read much lower. I don't know how familiar you are with tube amps but the load setting need to be higher with more drive.  A good trick is that both the plate and grid meter should deflect about the same when the amp is in tune.  The meters on the amp can be used to calculate output. If haven't already, call Ameritron, they will be happy to help you in any way.  
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WB2WIK
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« Reply #10 on: January 21, 2002, 11:20:31 AM »

Something is wrong with either the amplifier or the tuning process.  It was stated that with higher drive power, "both meters" (plate and grid current) can be "pegged."  That's a very bad sign.

The final adjustment of any such amplifier is to increase loading to reduce grid current, followed by a minor touch-up of the tuning to peak output power.  When the antenna system VSWR is reasonable, the 811H can be operated at >700W PEP output power with very little grid current indicated.  Crank the LOAD control clockwise, to decrease load capacitance and increase antenna loading.  If you do this while watching the grid current, you'll see it comes down.  The best adjustment for any such amplifier, including the 811H, is maximum output power achievable with minimum grid current.  On the 811H's I've used, I could get 700W output with <100mA grid current.

Thus, I would surmise that either this particular amplifier is defective (bad tube or tubes, or bad plate tank components that won't allow tuning for resonance), or the operator is not tuning it properly.

WB2WIK/6
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KC4KGU
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« Reply #11 on: January 21, 2002, 02:38:34 PM »

OK.  Here's what I've got.

7.0 Mhz
SWR = 1:1 (needle doesn't move)
Drive = 60W

Load = 4.5
Plate = 7.5
HV = 1550V (while TX)
Ip = 650mA
Ig = 185mA
Output (as indicated on the MFJ-989C) = 600W CW

If I switch to SSB and drive with PSK31 software I get:

HV = 1600V (while TX)
Ip = 500mA
Ig = 100mA
Output (as indicated on the MFJ-989C) = 600W


Is this more in line with what it should be?

73 de kc4kgu
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WV4I
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« Reply #12 on: January 22, 2002, 05:42:18 PM »

Hope this helps, from my AL-811H amp:

-Exciter: FT-990 w/built in SWR and Power Out meters
-Daiwa Watt Meter
-MFJ Dry Load rated 1.5kw
-AL-811H
-7.0Mhz
-SWR@FT-990>AL-811H=1.1 or less
-Drive=65w
-Load=4.3
-Plate=7.5
-HV=1525(idle), 1225(load)
-Ip=640
-Ig=135
-Power Out re Daiwa meter to Dry load = 560 watts

Ameritron advertises the AL-811 as 600w out PEP SSB, 500w out on CW, and 400w out RTTY. Extrapolating out with one extra tube and an efficiency of 60%, the numbers you're seeing and I'm seeing are consistent
with their claims.

Overall, I'm quite pleased with this amp. For the money, it's hard to beat. For comparison, I have an old Hallicrafters amp using a single 3-400. Only problem is that it requires a separate VERY heavy power supply. It is built/designed far better/more rugged than the Ameritrons, but would also cost far more today.
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WB9WHE
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« Reply #13 on: January 28, 2002, 11:21:59 AM »

I also had an 811H and a 986C tuner. Great little amp! Two things to keep in mind:

FIRST:  Remember that the MFJ tuner is NOT A TRUE PEAK READING meter. It is just fine for RMS/AM/FM modes...but it will allways real "low" for PEP.

SECOND: My 811H never put out 800 wats on 10 meters, because the amp was not all that efficent on 10M. So what power do you get on 20M?
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WA4DOU
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« Reply #14 on: January 30, 2002, 12:07:00 PM »

I don't understand why you want to run the amplifier so hard, despite what Ameritron says. If I remember correctly, RCA's plate dissipation rateing was 65 watts. I've read that some of these presently available 811A's are only rated at 45 watts. Using RCA's rateing, 3 of them form a composite plate dissipation rateing of 195 watts. Using 4 of them would be 260 watts. If the rateing is 45 watts per then 3 = 135 watts and 4 = 180 watts. At 67% efficiency the RCA tubes probably shouldn't be run at over about 400 watts output for 3 tubes and 520 watts for 4 tubes. With the inferior tubes the power ought not to exceed 300 with 3 tubes or 400 for 4 tubes.
  These are properly considered "light duty amplifiers." Run the hell out of them if you think a db or 2 is a good tradeoff for poor tube life. I don't think the trade is worth it.
  My above references to power are properly understood as c.w. power out. On ssb the plate voltage doesn't "sag" quite as much at a sylabic rate and therefore power output is a little higher. If the amp isn't being driven hard then this is not detrimental to the tubes as the output is only hitting these peaks on occasional voice peaks.
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