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Author Topic: AL-811 Newbie Questions  (Read 21504 times)
N3QE
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« Reply #15 on: January 11, 2013, 10:07:06 AM »

After reading about the troubles with this amp, I think I will not buy one.  But I do have one question:  Are the 572 tubes better to use in this amp or do they have the same problems as the 811s

Well, hams have been using 811A based amps for 50 to 60 years at this point, and having worked with several over the years (including Collins) and owning an Ameritron, I can tell you that the Ameritron's are the best of the bunch. This is not bleeding edge technology. The Ameritrons are highly evolved designs with the best bang for the buck.

Since you told us you aren't buying an Ameritron AL-811... why the interest in swapping out the tubes in one?

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W8JX
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« Reply #16 on: January 11, 2013, 10:43:52 AM »

AL-811HD HF AMP, 800W, (4) 572B TUBES, US 120VAC.  So if I read your reply correctly, then this amp from Ameritron should not work well either?  At $1250, it is a lot of money to spend on an amp that has "no reserve power left in the power supply".
Or am I reading into your last comment?

Rick wn2c

It is called marketing. Print a HD on it and it is magically a different amp. That being said  572's can actually have shorter lie span in a 811H or HD because the tube may never get hot enough to stay gettered and may arc over internally prematurely due to gas build up. In  3 tube amp you can run the harder.
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N4CR
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« Reply #17 on: January 11, 2013, 01:03:34 PM »

After reading about the troubles with this amp, I think I will not buy one.  But I do have one question:  Are the 572 tubes better to use in this amp or do they have the same problems as the 811s

Don't believe everything you read. These are good amps for the money and 811 amps of this design or one so similar you have to study to tell them apart, have been around for 50 years. Some tubes don't take abuse well at all and the 811 falls into this category.

If you tune this amplifier quickly and correctly and don't over drive it, then 811a tubes should last many years.

If you abuse an amp, mistune it, overdrive it and generally otherwise melt the plates of 811A tubes then the 572 tubes will last longer. A LOT longer.

I've opened many AL-811 (and H) amps only to find the plates melted. This is not the fault of the amplifier and new tubes bring them back to life. In my opinion, if there had been 572's in those same amplifiers,  they would have still been working because there's not enough power supply in these amps to melt 572's graphite plates.

And, that is why Ameritron came out with an amp with 572's in it. Because people abused the 811's and melted the plates out of them. Will 572's getter? Probably not.

If you double the investment, you can get a better amp. That's really the bottom line.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K4RVN
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« Reply #18 on: January 11, 2013, 05:12:44 PM »

I will be anxious to read if the thread starter found out what was causing the 80 meter loading problem. Have you checked the padders? I just don't see how 160 meters would load with bad padders and 80 meters would not. Please follow up and post what you found and I would appreciate it as I have an 811 three tube.

Frank
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W6JHB
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« Reply #19 on: January 11, 2013, 06:38:59 PM »

Have no fear - I will update this thread when I've gotten back into the amp. I had spoken with Rick at Ameritron day before yesterday and the engineer he spoke with (back room guy) said that "maybe" my 360 pf cap was bad. In any case, they mailed me a replacement 360 pf and a 500 pf cap. I got them in this afternoon's mail. THAT was fast shipping!! I hope to pop the cover tomorrow (Saturday) and see what I can do. Rick said to first try replacing the 360 with the new one they shipped. If that didn't fix it, to pull the new 360 and put that second 500 in it's place, giving me a total of 1,000 pf padding. I'll post back what the results are.

In the mean time I've been tearing up our home intercom system, adding ferrite beads on every lead I can. What's been happening is that the speakers on each intercom unit (there are five of them) thump when I operate 40 meter CW at 450 watts out. Doesn't happen with I run the K3 barefoot at 100 watts - only at high power. As I type this note, the intercom system is in total dis-assembly state as I put on the ferrites. Of course, when they built the house in 1990, they didn't leave a lot of slack cable, so on quite a few leads I've had to solder in four or five inches of extension so that I can wind the cable through the bead several times. If all this doesn't resolve the issue, I may have to get out the .357 magnum and put the darn thing out of my misery!  Grin
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Jim / W6JHB
Retired in Folsom, CA - and loving it!!!
WN2C
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« Reply #20 on: January 11, 2013, 07:20:40 PM »

W6JHB  Jim, I didn't mean to hijack the thread.  Please let us know what you find w/ the amp.

Putting the intercom system out of it's misery (and yours) may be the easier route to go!

Rick  wn2c
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W6JHB
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« Reply #21 on: January 11, 2013, 08:35:07 PM »

W6JHB  Jim, I didn't mean to hijack the thread.  Please let us know what you find w/ the amp.

Putting the intercom system out of it's misery (and yours) may be the easier route to go!

Rick  wn2c
No problem! Got the intercom fixed - put ferrite beads on every wire entering the control box, in addition to the wires going to each remote unit. No more RFI hitting the intercom!! Now I can concentrate on that 80 meter loading issue on the amp. Stay tuned (literally!).

Jim / W6JHB
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Jim / W6JHB
Retired in Folsom, CA - and loving it!!!
W6JHB
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« Reply #22 on: January 12, 2013, 10:35:59 AM »

This morning I removed the 360 pf cap that was factory installed. Put it on my meter and it read 385 pf. The new one I got from Ameritron read exactly the same, so I did not bother inserting it in place of the factory installed cap. Instead, I went directly to plan "B", which was to put the second 500 pf cap in parallel with the original 500 pf cap. Put the cabinet back together and fired up the K3 and amp. It works better, but not perfect. On 3.560 mHz, with 70 watts of drive from the K3, I get 475 watts out, with Load at 1.5 and Tune at 3.0 - I'm sitting at 450 ma Ip and 100 ma Ig. Up ten more kHz (3.570) and the load sits at 2.5, Tune at 3, Ip at 475, Ig at 90 and about 475 watts out. However, moving to the bottom of the band, 3.510 - not so good. At that frequency, even with 80 watts drive, the Load goes to zero, with Tune at 2.75 - 525 ma Ip and 90 ma Ig. So, it looks to my untrained eyes that 1,000 pf is still not enough for the very bottom of 80 meters. I could care less about 75 SSB, so adding more to make the CW part of the band work "may" be the answer. I was tempted to slide that new 360 pf cap in parallel with the two 500's already there, but I'll wait to speak with Ameritron on Monday and see what they say. One poster replied that he had moved the tap on the tank coil a bit. I hope I don't have to do something that drastic!

As a side note, I took another look at the 160 tuning data. No problem. On 1.810 kHz, with 50 watts drive, the Load sits at 5, Tune at .5 and I've got 375 ma Ip, 90 ma Ig, 450 watts out. And yes, the antennas for 80 and 160 ARE different. Both are Inverted L's and both are resonant at the bottom of the band.

Dang 80 meters - the ONE band I really need some oomph in my signal!! Well, I'm not done yet, so once again - stay tuned.
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Jim / W6JHB
Retired in Folsom, CA - and loving it!!!
K4RVN
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« Reply #23 on: January 12, 2013, 10:57:58 AM »

The procedure that would identify the problem is with the amp, or the antenna system would be to use a dummy load straight off the antenna connector on the amp. Perhaps you have done this and I missed it. Anyway good luck. I still will be anxious to catalog your solution for future use if I ever have the problem. Thanks for the post.

Frank
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W6JHB
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« Reply #24 on: January 13, 2013, 10:59:20 AM »

Frank - I have NOT tried the amp with a dummy load, as the only one I have at this point is a 300w air-cooled unit.

However I did some more testing this morning. Thought I'd explore as many avenues as possible before I either called Ameritron or heated up the soldering gun again. The testing I've been doing had been with my 80 meter Inverted L with a K2AV FoldedCounter Poise (FCP). I have an AIM-4170C analyzer and connected it to the Inverted L this morning, just to be sure I was not messing with a broken antenna! This antenna has a flat 1.4:1 or better SWR from just below 3.500 up to 3.600. The impedance showing on the '4170 graph runs from about 40 to 42 ohms from 3.500 to 3.600. Return loss runs from 19 dB to 24 dB in that same frequency range. Phase is around -6.4 in this range. All in all, it appears to me that this antenna should be liked by just about any tuner, exciter, or amp. In fact, the K3 and LDG AT-600ProII have no issue "tuning" it. I did the amplifier Loading / Tuning testing with this antenna going through the LDG tuner AND with it in bypass mode. No change in the readings - the Load control winds up down at zero when I'm on 3.510 and moves up into the 2-1/2+ range up at 3.570.

So, this morning I tried a different antenna with the amp. This is an 88-foot long doublet at 45 feet. It goes from the LDG tuner through six feet or so of RG-8X into a home brew 1KW 1:1 balun, 100 feet or so of 450 ohm ladder line, 15 feet or so of 600 ohm open line and then the antenna. With the amp in standby and the LDG tuner in bypass, I can turn on the K3's tuner and surprisingly it is able to get a match to the antenna. I turned off the K3's internal tuner, took the LDG out of bypass and told it to give it a try. It was also able to get a 1.5:1 or so match to this antenna. OK, now I put the AL-811 into Operate mode. Hmmmmm.... I was able to load it up without the Load control going to zero. When fully "tuned", the amp had it's Load control sitting at about 3. However, even with 90 watts of drive, I was unable to get more than 400 watts output. Interesting, but I don't want to use this antenna to operate - it's pretty much an NVIS antenna on 80.

So, now I'm confused. Why would the amp balk at operating properly with what is, in my view, at very well tuned antenna, but instead work fairly well with one that must be off the charts as far as resonance without the tuner in line? Arrrghhhhhh!!!!! Huh
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Jim / W6JHB
Retired in Folsom, CA - and loving it!!!
KF7CG
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« Reply #25 on: January 13, 2013, 01:31:28 PM »

The reactance present as part of the antenna impedance is such that it counteracts enough of the capacitive reactance of the tank circuit to prevent obtain a good match to the antenna. Your antenna tuner if it would handle the power can solve the problem. If you were to use an antenna analyer on this antenna I expect that though you might get a reasonable SWR, the inductive reactance of the antenna is enough to mess up tuning. Your amplifier tank circuit is performing the function of both tuner and amplifier tank circuit and doesn't have enough capacitance to accomplish this.

KF7CG
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K4RVN
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Posts: 778




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« Reply #26 on: January 13, 2013, 01:44:55 PM »

Tuned input not correct on the amp, tank coil maybe tapped a winding off or so are a couple of things. I would certainly check the solder joints in the 80 meter switch position as well as  on the coil. The sure fire way to check it would be to connect a watt meter to the amp, then a dummy load after that. If your dummy load is rated at 300 watts, you could make the hook up, use 20 watts driving power, then turn drive up to 60 with a fan blowing on a dry dummy load. Peak the load and plate for max out. This would have to be done in a hurry on power exceeding the dummy load rating. If the watt meter indicates over 400 watts for a couple of seconds then you know the amp is OK. Of course it would be best to borrow a higher rated dummy load as there is always a chance of burning the  underated load. Ameritron can tell you the coil turns count for the 80 meter tap. The swr readings on an antenna that is not loaded with power can change under power which may not show up with an analyzer. Besides that the 811 amp will load 2 to 1 impedance OK so I am suspect of your antenna system which includes all the components  in the 80 meter feed to your antenna. No real scientific reason, just a hunch.

Good luck and I hope it works out to your satisfaction.

Frank
« Last Edit: January 13, 2013, 01:48:07 PM by K4RVN » Logged
KU6X
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« Reply #27 on: January 13, 2013, 03:27:15 PM »

Why don't you just add a few hundred pF at the antenna (use an SO-239 Tee at the amp's output)
You shouldn't have to go inside the amp. Or, just use a tuner and mistune it a bit so the amp will load properly.

John, KU6X
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K4RVN
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« Reply #28 on: January 13, 2013, 04:49:19 PM »

I meant to write 2 to 1 SWR. Can correct it in my post.
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W6JHB
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« Reply #29 on: January 13, 2013, 07:19:53 PM »

The reactance present as part of the antenna impedance is such that it counteracts enough of the capacitive reactance of the tank circuit to prevent obtain a good match to the antenna. Your antenna tuner if it would handle the power can solve the problem. If you were to use an antenna analyer on this antenna I expect that though you might get a reasonable SWR, the inductive reactance of the antenna is enough to mess up tuning. Your amplifier tank circuit is performing the function of both tuner and amplifier tank circuit and doesn't have enough capacitance to accomplish this.

KF7CG

But, as I posted, the reactance on that Inverted L is almost zero, so I don't understand why you feel that the reactance of the antenna counteracts the capacitance of the tank circuit. The amp IS followed by a tuner - the LDG AT-600ProII, which I figure would deal with any inductive or capacitive reactances as it finds a match. At any rate, the tuner has the ability to add C or L values to what it's computer came up with, so I can try simply adding some C to it after it goes through a tuning cycle and see if that makes the AL-811 happy. Will give that a try on Monday morning.
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Jim / W6JHB
Retired in Folsom, CA - and loving it!!!
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