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Author Topic: Which amp to start with?  (Read 46948 times)
W8JX
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« Reply #15 on: January 14, 2017, 09:18:55 AM »

Stay away from the 811 or 572 b tube amps. You can get tubes but they are very expensive and not as robust as the 3-500 tube that will probably last your life time it taken care properly.

While I agree that a 811 is not robust at all not so with a good 572. There are some old 572's 40 years old still going strong and some high quality reasonably priced 572's on market now too.(I have 4 ea 572's in my Detron dated 1985 that still will make 1000 watts without a fuss and 55 to 60 watts of drive too)  As far as a modern 3-500 lasting a lifetime, not hardly as not are like tubes made 40 years ago. While they can last many years if used properly the AL 80B does not properly cool it (at rated 500 watt dissipation the tube is supposed to have a chimney with air flowing through socket and over tube, not just a small muffin fan blowing across it) and to run 1000 watt or more with a AL80 you have to exceed tubes ratings and cooling and it will shorten life. That being said a AL80b is a solid 850 watt amp and a but marginal at 1000 to 1100 watts because tube life will suffer.
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K1HMS
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« Reply #16 on: January 14, 2017, 10:45:28 AM »

I would look for a Al-80b for good, clean, and reliable power. Second choice would be a ALS-600, but don't over drive it and watch the match. Forgetting to turn the band switch or tturning down the drive will cost you.

But for the same money you would likely have more fun with a Hex beam due to all of the activity you would hear and work.
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VK3BL
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« Reply #17 on: January 14, 2017, 06:23:31 PM »

While I agree that a 811 is not robust at all not so with a good 572. There are some old 572's 40 years old still going strong and some high quality reasonably priced 572's on market now too.(I have 4 ea 572's in my Detron dated 1985 that still will make 1000 watts without a fuss and 55 to 60 watts of drive too)  As far as a modern 3-500 lasting a lifetime, not hardly as not are like tubes made 40 years ago. While they can last many years if used properly the AL 80B does not properly cool it (at rated 500 watt dissipation the tube is supposed to have a chimney with air flowing through socket and over tube, not just a small muffin fan blowing across it) and to run 1000 watt or more with a AL80 you have to exceed tubes ratings and cooling and it will shorten life. That being said a AL80b is a solid 850 watt amp and a but marginal at 1000 to 1100 watts because tube life will suffer.

I agree.  The 811a is not in the same league as the 572b.

Despite what you may find written over at W8JI's website, neither the filaments nor the grids are the same as the 811A. Any cursory glance at both tubes will show this.

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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
N3DT
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« Reply #18 on: January 14, 2017, 07:01:42 PM »

I can vouch for the 80B. It's a solid amp with a good tube and can be had for under $900, sometimes delivered. I've heard of them for much less. Nice if you can find local and shown. No disappointments if it works. I'd stay away from the older amps, they're even older than the 80B and will most likely have issues that you'll spend more money on than if you just bought an 80B that is guaranteed to work and still in production. Puts out a solid 700-800W which is the sweet spot before you have to go to something better than RG8X. As far as your vertical, I never met one I liked. Get a real antenna, dipole at 20' if that's what you can do. Stick to a single or 2 bands for a while, 40 and 20 are good choices with 40 CW the prime choice. You can work the world on 40 CW, especially with the sunspots where they are. Improve your antenna first, it's cheap. Power is nice but only gets you a few S units at best and you won't hear any better. A better antenna will get you there both ways, RX and TX, before the amp. Believe me.
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KB1SNJ
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« Reply #19 on: January 14, 2017, 09:23:24 PM »

Ok I have listed in my notes every amplifier suggestion and antenna suggestion, and noted the tuner consideration and RF management.

because of the replies I can now at least fundamentally see the basic areas to address and I agree that the antenna needs to be dealt with.

here's a few thoughts and questions. I dont necessarily need answers as this was an amplifier topic and I got some great suggestions thank you! but these things are unknowns as to what would be best.

It also makes me wonder how irregular a ground plane can be.

For example I can bury radials all around the house perimeter (and I just realized that I have 2 fairly short radials off the vertical now one running East, one running west, and a 8ft ground rod right under it). my house is roughly 20x30 and against the boundary on 2 sides, so I can run a radial around the perimeter like a loop, what would that do for RF coming back as well as a pattern if it were under a vertical roughly in the middle above the house?  and does the vertical have to extend down to the ground?  another question is that my property is 40ft wide and faces east west the long way. I suppose I could erect poles at each side maybe at the back lot corners,  and that would span 40ft with the broadside facing east-west.  I wonder what min height would be needed? (I will look that up). what would it take to work 160-6 on a horizontal wire/dipole that spans only 40ft? use traps or coils? that end of my lot faces west, I suppose I could add a reflector wire some distance forward (east) to put some gain to the west?



as to the tuner, I didnt think of the fact that the tuner is between the amp and antenna feed point (duh) and must handle the full power. another cost.

the antenna suggestions are as usual confounding because of the constraints of my lot and building shape. at least i have the 2 big trees and an unlimited budget (KIDDING!)

originally this was "I have an antenna that I can at least match on most bands. if its not very efficient, I can add power".  now I know that wont be optimal due to RF (lack of ground plane), and other things.

btw when I had my bent G5RV over the house RF was worse, tripped a GFCI and fried my router as well as jammed my computer monitor requiring it to be power cycled. the new vertical is not as bad, only the monitor is affected (and the headphone mixer cant be used). so there's still RF inside despite the ground rod and two radials.






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KK4YDR
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« Reply #20 on: January 14, 2017, 10:09:54 PM »

I love how these "What should I buy" threads turn into whos opinion is more important than the next and how much one thing sucks more than another and how it goes around and around.

Just get what you can afford. Get a better or modify your existing antenna to be better. And just be happy.

I recommend the junk 811 as so many people call it because I owned one in the past and it wasn't junk in the least darn bit. I only sold it to get a legal limit amp to upgrade. It was a good little beginner amp for sure.
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KB1SNJ
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« Reply #21 on: January 14, 2017, 10:13:32 PM »

I've found the replies very helpful. They showed me that i cant just buy power and be happy because of likely RF issues and it's about the antenna before the amp. So I appreciated all the info.
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VK3BL
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« Reply #22 on: January 14, 2017, 11:29:50 PM »

btw when I had my bent G5RV over the house RF was worse, tripped a GFCI and fried my router as well as jammed my computer monitor requiring it to be power cycled. the new vertical is not as bad, only the monitor is affected (and the headphone mixer cant be used). so there's still RF inside despite the ground rod and two radials.

I've operated a station with an antenna a similar distance - around 20ft.  I did have one brand of access point that would lose its settings when it TXed at QRO, but it was fed with a 15ft network cable so its not surprising.  Everything else was fine though, although if I used a set of headphones with the rig I'd occasionally get noise in them while TXing, but that was solved with a few turns through a ferrite core.

Could you run a 52ft G5RV without bending it?  That would give you better balance, and you could use all bands 40M up, and probably 80M for local contacts at lower.

If you still have the bent G5RV up, it would we worth seeing if a different balun improved things.  A properly designed 1:1 current balun should keep RF off the outside of the coax and minimal (other than radiated) in the shack.

Keep digging, its definitely possible to operate QRO close to your antennas.  DXPeditions do it all the time, as would many amateurs.

For a balun, buy a FT240-43 core from Fair Rite, and wind 12 turns of LMR-195/RG-58 round it.  Thats as close to the perfect 'do everything' 1:1 balun as you're going to get, and its good for well over 1Kw continuous.

You can add the aforementioned balun to your existing setup, just after the 9:1 at the feed point.  The 9:1 is maybe/probably helping with matching on some bands, but it is likely its doing little to stop RF getting back into the shack via the coax.

« Last Edit: January 14, 2017, 11:35:53 PM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
W9IQ
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« Reply #23 on: January 15, 2017, 03:09:59 AM »

Chris,

Since you are in a compromise situation, I would recommend running any radials you can. It will likely improve the efficiency of your antenna and it may reduce RF in your house. The antenna pattern won't be predictable but it is better than the alternative.

Try to keep the bottom of the vertical wire at the same height as where all the radials meet.

A good 1:1 choking balun where the coax connects to the antenna will also help reduce RF in the house.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
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« Reply #24 on: January 15, 2017, 03:29:56 AM »

Quote
Keep digging, its definitely possible to operate QRO close to your antennas.  DXPeditions do it all the time, as would many amateurs

While this is probably true, it does not properly recognize that in the US, a ham wishing to operate QRO is required by FCC regulations to carry out an RF exposure assessment. If the RF exposure is above the regulatory limits, the licensee is required to bring them into compliance before operating QRO.

- Glenn W9IQ
« Last Edit: January 15, 2017, 03:40:37 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W8JX
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« Reply #25 on: January 15, 2017, 04:32:02 AM »

I recommend the junk 811 as so many people call it because I owned one in the past and it wasn't junk in the least darn bit.

Without doubt the AL811 is the cheapest built and most troublesome amp on market by far. To suggest otherwise is very misleading. Landfills have thousands of burnout/melted 811 tubes in them from AL 811 amps. If you use one and run it 30% below rated output it may last for a while but it is very easy to damage tubes in it. The funnest part of this is that Ameritron makes a 800 watt rated AL811H and a 850+ watt rated AL80B yet the AL80B has roughly twice the transformer mass and about 250% more safe plate dissipation in one tube than a AL811 has in all 4 and yet some cannot connect dots and see what a cheap over rated amp it is. There is no other amp made in last 40+ years (except for a few sweep tube amps) that regularly exceeds tube rating for "normal" rated operation. None! If old Heathkit SB200 had been built as cheap and over rated as much as AL811's they would of disappeared decades ago rather than still being quite viable today. It was rated at about 600 watts out with a safe dissipation of 320 watts. The 600 watt AL811 has a safe continuous dissipation of 135 watts. Which is a real amp?
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N8FVJ
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« Reply #26 on: January 15, 2017, 06:50:28 AM »

Quote: 'I have never heard of someone being killed by a tube amp but thousands have died from 120 volt wall current.'

I heard. The ham was on the air in the 1990s on 3898 when it was famous. In the round table a ham did not come back. It was later found he tripped and his hand entered the top of an uncovered home brew amp. He was electrocuted.

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W8JX
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« Reply #27 on: January 15, 2017, 07:19:59 AM »

Quote: 'I have never heard of someone being killed by a tube amp but thousands have died from 120 volt wall current.'

I heard. The ham was on the air in the 1990s on 3898 when it was famous. In the round table a ham did not come back. It was later found he tripped and his hand entered the top of an uncovered home brew amp. He was electrocuted.


Anyone stupid enough to use a HV amp in normal operation without a cover on it is asking for trouble. It is not the fault of it being a HV amp but rather the fault of the operator. Hard to make it idiot proof. Plus if it was a commercially built amp it likely has a HV interlock on cover that you have to disable for this to happen
« Last Edit: January 15, 2017, 07:37:25 AM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
KB1SNJ
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« Reply #28 on: January 15, 2017, 10:46:58 AM »

Regarding the RF issues, I had bought some snap together ferrites years ago and tried them to keep the RF out of the headphone mixer and monitor to absolutely no avail. I think ferrites are tricky, there's different compounds and shapes resulting in varying electrical properties. I had another issue never resolved, with a 12dc-120vac voltage inverter trying to stop the hash from getting to an older tube receiver in my camper (which is quiet on wall power). Tried wrapping the power cord through #43 and #61 Ferrites did nothing.  Adding brute force EMI filters did nothing. Buying a better inverter (samlex) and grounding it, cut the noise about in half. Then I ordered a EMI cord http://emceupen.com/_files/content/pdfs/na201_201507161230060084.pdf
and again, wall power = quiet, inverter power sends hash to the receiver. No noise when running the inverter but radio is on wall power (unless its very close). So the above EMI cord, or 43 and 61 ferrites did not stop whatever is travelling down the power cord.

So my track record on stopping RF from my antenna from getting into things, or whatever is coming from the inverter is batting a zero.

As to the HF antenna issue, obviously I do need to implement an antenna that radiates all the RF and not from the feedline back into the shack/house. Because even if ferrites etc worked to block it from my equipment, I would need a forklift load of them to cover all the cat5, power cords, speaker cables, and everything else.

As to the inverter noise issue, I was surprised at how resilient it really is, making it through ferrites, brute force filters, and that very good EMI power cord!

BTW, is that noise from the inverter RF or something else?



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W9IQ
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« Reply #29 on: January 15, 2017, 12:55:13 PM »

Chris,

RFI problems are often by their nature often difficult to cure. There are engineering professions that deal exclusively with EMI and RFI and there can be very frustrating days even for these well practiced engineers.

Based on your description of your antenna, I would work on reducing common mode current as this will follow your coax into your shack and it brings your RF (and effectively your antenna) that much closer to the balance of the house. Adding a quality choking balun at the feedpoint of your antenna and adding radials (counterpoise) to your antenna will help to reduce the common mode current.

Secondarily, your antenna is located very close to your house. You are therefore subjecting many electrical / electronic things in your house to high RF levels. Most consumer electronics where never designed to work properly in such conditions. Sometimes you get lucky and things work. Other times they get quirky. The most effective cure is to reduce the RF in the house. Possible solutions (in addition to reducing common mode current): move the antenna further away, use a directional antenna pointing away from the house, and lowering your transmit power. Failing success with these, you can attempt to apply counter measures on each effected device with varying degrees of success.

To your inverter question, yes the noise is RF.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
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