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Author Topic: Ameritron AL-811 'fixes'  (Read 17597 times)
N8FVJ
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Posts: 910




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« on: January 11, 2018, 07:12:12 PM »

I have stood behind the entry level AL-811 despite much criticism. Many hams have come to the fact it is a reasonably reliable amplifier. But, Ameritron did over-rate the AL-811 power output with the low plate dissipation of the 811A tubes. The old RCA 811A were 65 watt ICAS tubes, but the newer tubes without the horizontal fins are about 55 watts plate dissipation at best. The amp will perform at 600 watts PEP, but tube life will suffer. Even your SSB speech processor will increase the duty cycle, And, for higher duty cycle modes I recommend 350 watts CW and even less output with SSTV/RTTY. The only reliable 811A tube is the Russian G811. These tubes are available on ebay for about $20 each.

The AL-811 can be upgraded to a more reliable amplifier of about 700 PEP watts out with 75 watts drive. I have not measured the IMD products at 700 watts PEP, but suspect they are acceptable.

First upgrade is replacing the 450 volt DC power supply capacitors. I use 500 volt 220uF snap in capacitors. The four capacitors are available at Mouser or Digikey for about $30. Frankly, although I read a capacitor can be operated at full voltage per the manufacture at less than 80C operating temperature, I want a 50 volt per capacitor buffer. 500 volt capacitors will provide that at 120 volts AC line input.

Second issue is I want a soft-start module to limit vacuum tube filament current inrush. Soft starting the tube filaments should lead to increased tube life. It is a fact tubes last longer at continuous duty use vs many on-off cycles. Harbach Electronics sells soft start modules. I bought the Heathkit SB-200 model for 120 volts that works well with the AL-811 amplifier. Harbach also sells 240 volt soft start modules.

Third issue are the 811A tubes. I use NOS Cetron 572B tubes. I will not pay the same for inferior Chinese 572B tubes. The Cetron 572B are far superior to the 811A. At 160 watts plate dissipation three tubes are close to a 3-500Z tube dissipation. The Cetron 572B tubes in new old stock (NOS) will cost about $80 each. The Cetron are getting somewhat scarce, but placing a want ad at QTH.com will get you a set of three tubes in about a week. The Cetron also come up on ebay at times.

I bought my amp for $450 shipped. I bought three tubes for $230. Also paid $30 for capacitors & $30 for the soft-start module. I have $710 in my amplifier with tubes that will likely last me for perhaps 3000-5000 hours.

Or, the next step up in an amplifier is the Heathkit SB-1000, Ameritron AL-80A or AL-80B. These are very good amplifiers & better built vs any AL-811! However, the cost is about $1000 used for the Heathkit SB-1000 or Ameritron AL-80A/AL80B amplifier and the tube condition is unknown. (I would not buy the early AL-80 amp).

So, the AL-811 used is a good deal IMO. The more expensive used AL-811H is not a great deal when one considers the three Cetron 572Bs in the AL-811 amplifier. And, both amps use the same power transformer. The AL-811 at 700 watts PEP output does not tax the transformer in the least.

However, if you want to take a chance on the 811A tubes, four 811A tubes beats three 811A tubes. I would limit the AL-811H at 600 watts PEP with the Russian G811 tubes only.
« Last Edit: January 11, 2018, 07:15:25 PM by N8FVJ » Logged
W8JX
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« Reply #1 on: January 11, 2018, 07:48:06 PM »

The AL-811 at 700 watts PEP output does not tax the transformer in the least.

You are being a bit to generous here. That transformer is not that stout.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
N8FVJ
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Posts: 910




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« Reply #2 on: January 11, 2018, 08:04:34 PM »

The AL-811 at 700 watts PEP output does not tax the transformer in the least.

You are being a bit to generous here. That transformer is not that stout.

17lbs is sufficient. Holds 1500 volts at 800 watts PEP out, but I operate at 700 watts PEP. I admit the 19lb Heathkit SB-200 may be a little stronger.
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VK3BL
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« Reply #3 on: January 12, 2018, 12:54:14 AM »

Second issue is I want a soft-start module to limit vacuum tube filament current inrush. Soft starting the tube filaments should lead to increased tube life. It is a fact tubes last longer at continuous duty use vs many on-off cycles. Harbach Electronics sells soft start modules. I bought the Heathkit SB-200 model for 120 volts that works well with the AL-811 amplifier. Harbach also sells 240 volt soft start modules.

Adding a soft start module is like putting a huge spoiler on a small economy car.

I have burnt out every 811A type I could get my hands on, but not once have I snapped a filament.

in fact, the best thing you can do to increase tube life is to turn the amp off when you are not using it.  The filaments lose emission during idle.

I doubt the modification you've made hurts in any way, but I certainly don't believe it would be of benefit to the average AL-811 owner, especially if they are using '811A' tubes.

Anyway, it sounds like you've got a nice amplifier there.  The only thing I'd look into is the stability on 10M; normally 2x 572Bs require neutralisation for 10M, let alone 3. 

Despite what a well known Ham has written, the 572B cathode and grid ARE NOT the same as the 811A; a cursory glance at both tubes side by side is all that is required to verify this.

As you have mentioned, the 572B is a significantly better tube.

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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N2EY
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« Reply #4 on: January 12, 2018, 03:50:41 AM »

"Anything can be fixed if you replace enough parts"

The question is....if you start replacing parts with better ones, at what point does it stop being an AL-811?

New carpenter to old carpenter: "What do you think of my hammer?"

Old carpenter to new carpenter: "It looks nice but they just don't make 'em like they used to."

New carpenter to old carpenter: "How so?"

Old carpenter to new carpenter: "Look at my hammer. Had it 40 years.......of course, it's had six new handles and three new heads......"

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N8FVJ
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« Reply #5 on: January 12, 2018, 05:21:56 AM »

Despite what a well known Ham has written, the 572B cathode and grid ARE NOT the same as the 811A; a cursory glance at both tubes side by side is all that is required to verify this.

As you have mentioned, the 572B is a significantly better tube.[/b]

[/quote]

I know the 572B is not an 811A with just a heavy duty plate. The amp tunes differently into a perfect 50 ohm dummy load. A 1000pf replacing the 500pf fixed capacitor on the load variable cap allows full tuning range down to 3.5mHz at close to fully engaged and about 1/4 load cap engagement at 4mHz with 811A tubes. The 572B just allows full output at 4mHz with the loading cap at minimum capacitance. That is about 200pF less capacitance at 4mhz vs the 811A tubes. Both tubes were measured at 600 watts PEP output.
« Last Edit: January 12, 2018, 05:28:41 AM by N8FVJ » Logged
WY7CHY
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Posts: 1018




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« Reply #6 on: January 12, 2018, 07:40:43 AM »

While I have definitely been a proponent of the AL-811 series amps, I am not one for justifying putting too much time or money into trying to "Upgrade/Fix" this amp. At $400-$550 for the amp, (Depending on the model), it's a good amp for what it is. The only upgrade I'd recommend is getting the G-811 Ryazan tubes. After that, there's no real advantage. As for 572b tubes; I wouldn't invest $250-$350 for 572b tubes. Only if you happen to have them on hand or got them at dirt cheap price.

Guess what I'm saying is: Once you hit that $700-$750 price range, you'd be better off looking at a different/better amp. An AL-80A or AL-80B can be found for $900-$1000. You can even get solid state amps starting at the $1000 area. So; if you can save/spend $750 for an AL-811 series amp; with upgrades; you can definitely save up another month or two for another $250. And remember; Ameritron isn't the only manufacturer of amps. There's a lot of good amps out there.

Again; I have nothing bad to say about the AL-811 series amps. As long as you buy them used in the $400-$550 price range. Spend another $60-$80 for some Ryazan tubes (or use 572b tubes if you have them on hand) and ENJOY the amp. It will treat you right. If you're going to spend more than that, start looking at other amps.

Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
KM1H
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Posts: 5570




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« Reply #7 on: January 12, 2018, 08:37:48 AM »

Quote
First upgrade is replacing the 450 volt DC power supply capacitors. I use 500 volt 220uF snap in capacitors. The four capacitors are available at Mouser or Digikey for about $30. Frankly, although I read a capacitor can be operated at full voltage per the manufacture at less than 80C operating temperature, I want a 50 volt per capacitor buffer. 500 volt capacitors will provide that at 120 volts AC line input.


Ameritron does not use Snap In caps, unless it is a recent change that I am not aware of, and requires a PC board mod that many may not be able to do.
The old 70's style "computer grade" format is a simple screw terminal.
 and are around $10-11 each from Ameritron last I bought them for the senior series amps.

I agree that the transformer is fully adequate for 800W PEP and one of the best bargains for the DIYer or repair of other brand amps; Ive bought several.

While not cheap the current RFP and Machlett (Penta) 572B's are holding up well and Ive started up SB-200 6M conversions again.

I have not experienced any 572B loading problems on any band but it is drive dependent as with any other GG amp. It is always possible that the L coil is miswired/miswound or a wrong value fixed cap, this is MFJitron after all.
My amp bench has dedicated 20A 120V and 30A 240V feeds of about 25' from the main panel. Not all dummy loads are created equal and there is an outside chance of prior damage.  I use a custom built for RCA 3000W Bird and measure the big Carborundum resistor frequently since I do push it at times.

Carl
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N8FVJ
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Posts: 910




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« Reply #8 on: January 12, 2018, 12:06:00 PM »

Ameritron does not use Snap In caps, unless it is a recent change that I am not aware of, and requires a PC board mod that many may not be able to do.
Carl
[/quote]

Again, not true. A new CB board is not necessary. The snap-in capacitors fits in the CB screw holes. Bend over the snap-in capacitor leads and solder in place. A simple operation and all that is needed is soldering skills.
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KM1H
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Posts: 5570




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« Reply #9 on: January 12, 2018, 12:54:35 PM »

Quote
Again, not true. A new CB board is not necessary. The snap-in capacitors fits in the CB screw holes. Bend over the snap-in capacitor leads and solder in place. A simple operation and all that is needed is soldering skills.

I havent tried that, do others agree?

Do you have a photo to show your soldering skills?
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N8FVJ
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Posts: 910




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« Reply #10 on: January 12, 2018, 02:05:10 PM »

Quote
Again, not true. A new CB board is not necessary. The snap-in capacitors fits in the CB screw holes. Bend over the snap-in capacitor leads and solder in place. A simple operation and all that is needed is soldering skills.

I havent tried that, do others agree?

Do you have a photo to show your soldering skills?

I do not know how to put a picture on this forum. I been soldering for over 50 years. If the caps fit and they did, end of discussion! It is ok to be in error Carl. No big deal.
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KM1H
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Posts: 5570




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« Reply #11 on: January 12, 2018, 02:53:29 PM »

Quote
Again, not true. A new CB board is not necessary. The snap-in capacitors fits in the CB screw holes. Bend over the snap-in capacitor leads and solder in place. A simple operation and all that is needed is soldering skills.

Im just looking for confirmation...you got a problem with that?

I do not do Hammy Hambone repairs to customer amps and my soldering skills predate yours by a decade.

For photos:

https://www.eham.net/ehamforum/smf/index.php?action=printpage;topic=113912.0
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N8FVJ
Member

Posts: 910




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« Reply #12 on: January 12, 2018, 02:59:05 PM »

Quote
Again, not true. A new CB board is not necessary. The snap-in capacitors fits in the CB screw holes. Bend over the snap-in capacitor leads and solder in place. A simple operation and all that is needed is soldering skills.

Im just looking for confirmation...you got a problem with that?

I do not do Hammy Hambone repairs to customer amps and my soldering skills predate yours by a decade.

For photos:

https://www.eham.net/ehamforum/smf/index.php?action=printpage;topic=113912.0

No problem for conformation. But, I do have a working amp with snap-in caps. I agree it is not exactly a perfect appearing swap as the screw holes do show as I cannot bridge the solder across the screw hole. But, it is not truly unsightly and is under a cover. The amp will perform for many years. 500 volt screw type caps are rare & expensive plus will not outperform the snap-in type in this application.
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K9AXN
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« Reply #13 on: January 13, 2018, 07:46:24 AM »

Is there a complete list of fixes, reasons for, and opinion of successful or not available anywhere.  Best I can find is fragments.

The 811 series amp has the most profound love hate relationship of any ever built.

The whole story is incredibly complex and interesting.

Regards Jim
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MM0IMC
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Posts: 255




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« Reply #14 on: January 13, 2018, 02:12:16 PM »

Fixes for the AL-811(H)?

Better rear band switch, pain in the bum to replace and easily damaged.
Better case screws, as you'll need to remove them often.
Switches are a bit cheap and nasty.
Rear circuit is a pain to work on.

Fixing these would be a start...
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