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Author Topic: Which amp to start with?  (Read 46904 times)
KB1SNJ
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« on: January 13, 2017, 10:10:32 PM »

I know general question but I've seen numerous options in the classifieds, just looking for ideas and experiences.

I have a very tight lot, with a 50ft vertical above a 9:1 unun running 100watts. I really do not have much antenna options, no space for a ground plane array either.

A lot of stations that I can hear, cant hear me. So I think an amplifier may help compensate for the antenna deficiency.

Thinking that 1000 watts would be good. I have had issues with RF in the house tripping GFCI, etc but when I went to the vertical it seems to have gotten better (although my computer monitor still goes wonky with 100 watts)

Anyway, I'd need a robust amplifier because I am going to make mistakes operating initially. Budget is also a big issue.

ideas? experiences?




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KK4YDR
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« Reply #1 on: January 13, 2017, 11:08:39 PM »

Well I am sure you know this already. But an amplifier can only improve upon a poor antenna poorly. But a good antenna an amplifier can make it much better.

However, in the meantime from the sound of it and your limited options, if you have indeed exhausted all antenna options, an amplifier can boost your signal. I HIGHLY recommend seriously looking into your antenna situation before making a jump to an amplifier. My personal experience and many others will tell you that the amplifier is the L A S T item to place in the shack when all other elements have been perfect as much as you can. The antenna is 95% of the performance on the air and the other 5% is the amplifier realistically. I have heard stations running 1000 watts with absolutely poor signals that were hard to hear and found out that their antenna was pure compromise or junk overall. On stations with a great antenna you can hear them quite well without an amplifier then you will hear them exceptionally well with an amplifier.

With that being said - I recommend a few amps based on price range and want/need/performance in reality.

With amplification on HAM radio the first 500 watts absolutely makes the biggest difference, The next and rather large increase is going to 1 kw. Going to 1500 watts is really a waste of money except in the most extreme cases where it matters. Oh and it does make you louder without really increasing signal more than a KW.

If you are on a tight budget, and are willing to accept, or are comfortable with a beginner amplifier - Ameritron AL-811. The tubes are cheap as dirt and if you blow one just change it like a 20 dollar lightbulb.

If you have more money but don't want tubes, get the Ameritron ALS-600 solid state. Good for around 500-600 watts output.

If you want to spend more money, around the same as the ALS-600, I HIGHLY recommend the AL-80B. Single 3-500Z amplifier and is good for a realistic 700-850 watts. More and you are pushing the amp and tube hard.'

Where you say "Anyway, I'd need a robust amplifier because I am going to make mistakes operating initially. Budget is also a big issue."

This is where I recommend the AL-811 to learn on. It is robust in the sense that it is going to be hard to damage the internal components unless you are extremely wrong in your operating habits. The tubes are not made of $$$$$$$$ like more expensive ceramic tubes. They are inexpensive and quite literally pennies compared to say a 3cx800A7 or 3cx1500 tube over $1000 each.

Sometimes for a starter the best amp is the one with the cheapest tubes. I know you want robust and strong tubes, so if you don't want to learn by blowing up a few 20 dollar tubes then I recommend an amp that uses the 3cx1200A7. It is nearly indestructible except under the worst operating conditions. However, an amplifer that can run that tube is going to set you back minimum of 3000 dollars with the replacement tube over $1200-1300 each.

Good luck

« Last Edit: January 13, 2017, 11:12:00 PM by KK4YDR » Logged
VK3BL
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« Reply #2 on: January 14, 2017, 02:25:58 AM »

Thinking that 1000 watts would be good. I have had issues with RF in the house tripping GFCI, etc but when I went to the vertical it seems to have gotten better (although my computer monitor still goes wonky with 100 watts)

The long and the short of it is if you are having RFI problems at 100 watts, it will be a nightmare at 1000 watts.  More than likely, whatever is causing the RFI will burn out.

It sounds like you have an antenna efficiency problem.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
ZENKI
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« Reply #3 on: January 14, 2017, 03:24:26 AM »

Verticals are notorious for generation a  strong near field  equipment and noise which is close enough to pick up and radiate problems

Can you support a open wire fed 40 meter dipole, or even a 30 meter dipole  fed with  balanced coupler or  even a T match with a good external 1:1 balun.

Another option would be to use a Vertical like the Hygain AV640  up high on  a pipe or Rohn 25 section 20 to 30ft would be enough to give you a better signal and decrease the field strength.

If you can do that,  and then get a small Amplifier like an Ameritron AL80B, I dont think you will have  the trouble that you are having.

If you want to get on 80  and 40  only a coil loaded dipole will work a lot better for short contacts within the USA
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W8JX
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« Reply #4 on: January 14, 2017, 04:05:50 AM »

I suggest a few things. First change antenna as non resonant antennas are not efficient and are prone to common mode RFI too. These multi-band (via a tuner) non resonant verticals look good in ads but they are for convenience not performance.  I suggest you try a Hustler 6BTV placed as far from house/shack as possible and what ever radials you can fit in (they do not have to be a resonant length on ground). Next on amp, if you had a RFI problem, it will get much worse with power. Avoid a AL811 series amp. They are a over rated POS and eat tubes very easily (because of over rating). If you want a amp, for about same money as a AL 811 (or a bit more) you can get a used AL-80 series amp. It is a rock solid 850+ watt amp. you can push it to 1000 or so but remember that even from 850 to 1100 is not quite one db and will make no difference down range (the extra 250 watts is far more a state of mind/ego than a meaningful help down range) If you can find a clean SB-200 that has been rebuilt it is far more rugged/solid 500 to 600 watt amp than ANY AL811 amp hands down. (two 572's have 50% more safe dissipation than four 811's)

Scrap current antenna first then consider a amp.
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W9IQ
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« Reply #5 on: January 14, 2017, 04:12:57 AM »

Chris,

After reading your description of your antenna installation in the Elmers section, I would encourage you to go through the RF Exposure assessment procedure. My guestimate is that it will not be safe (or legal) for you to use a 1 kW amp in your situation.

If you do pass the assessment, you should then first improve your grounding/counterpoise situation and evaluate the suitability of your 9:1 unun and coax for the anticipated power with additional consideration for your elevated SWR.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
VK3BL
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« Reply #6 on: January 14, 2017, 05:22:56 AM »

Chris,

After reading your description of your antenna installation in the Elmers section, I would encourage you to go through the RF Exposure assessment procedure. My guestimate is that it will not be safe (or legal) for you to use a 1 kW amp in your situation.

If you do pass the assessment, you should then first improve your grounding/counterpoise situation and evaluate the suitability of your 9:1 unun and coax for the anticipated power with additional consideration for your elevated SWR.

- Glenn W9IQ

VK is probably different to you guys, but at HF frequencies with a vertical 1000 watts would be fine in terms of exposure so long as you are a good 20-30 ft from the antenna.  The best way of achieving this if you are too close to the antenna is to elevate it 20-30ft.

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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
VK3BL
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« Reply #7 on: January 14, 2017, 05:43:53 AM »

I have a very tight lot, with a 50ft vertical above a 9:1 unun running 100watts. I really do not have much antenna options, no space for a ground plane array either.

A few things here as well:

1) If you don't have a ground plane, and you're using a vertical monopole, your feed line is your ground plane.  Thats why you still have RFI issues with the computer monitor.

2) Unless your feed line is sufficiently long (think 100ft), you are almost certainly going to fry that balun on one of the bands you try @ 1000 watts.  Contrary to popular belief, baluns - especially 'ratio' baluns - generally only provide optimal performance on a few bands best case scenario.

3) What antenna tuner are you using?  Even my Palstar AT2K can't take more than 250 watts if I try to tune up a 52ft ladder line fed dipole on 80M - the antenna is simply too short electrically, presents a low impedance to the tuner, cooks the inductor and arcs a cap.  You may fair better if you have a less efficient antenna system (you do).

To put things into perspective, even a full 1/4 wave mono band vertical monopole with the typical 4-16 radials fed with 30-50ft of coax is going to be hard to get past 50% efficiency in a typical installation.  If its built well, the power loss won't be in components, but rather the feed line and the earth surrounding the antenna.

In summary, as much as I love amps, I just can't recommend you add one to your station at this stage.  You are already reporting RFI issues at the 100 watt power range, and I highly suspect you'll blow something up if you run at 1000 watts.  You really need to get some radials down.

If you really must have an amp, my advice is to pick a band and setup an efficient mono band antenna, or a G5RV variant.  I assume you can't install a dipole, so as far as verticals go, the best bet is probably something like a 43ft vertical with the tuner at the feed point (think MFJ-998RT) and a 1:1 current balun just before the ATU.  You would still need radials. 

If you truly cannot manage a horizontal dipole or a vertical with 8+ radials, your only real option is a vertical dipole.  Gap antenna and a few other companies make them, and they truly are your only option if you want to run 1kw into a vertical with no radials and not suffer RFI.

As far as first amps go, a very good to excellent condition second hand AL-80B should be at the top of your list.  Run it at 800 watts and it will take a licking.  They are a (relatively) modern design, and full manufacturer support including all replacement parts are available.  The AL-80 series mainframe is simple to work on, and the 3-500ZG is a monster tube with 500 watts+ of dissipation.

Only consider an AL-811 series if funds are really limited, and you only intend on once a week SSB Phone usage.  Tube life will be pretty short irrespective of how hard you drive them, as they are biased to idle at around 35-40 watts per tube.  Thats over half the tubes rated dissipation (45w CCS / 65w ICAS) just in idle bias current, and its continuous.  On the other hand, the tubes are plentiful and cheap, but you should only expect 500-1000 hours from a good set.

Much better to buy an AL-80B if you can.  It will literally pay for the extra cost in tube savings with a few years or regular use.
« Last Edit: January 14, 2017, 05:52:49 AM by VK3BL » Logged

J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
W8JX
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« Reply #8 on: January 14, 2017, 06:40:26 AM »

Only consider an AL-811 series if funds are really limited,

If funds are that limited do not waste money on a AL811 and save for a real amp. That being said though a SB200 in good order can be had for a lot less than a new AL811 and is a MUCH better amp. The fact they are still in use and demand nearly 50 years after they were first designed tells you a lot about the ruggedness of design.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W9IQ
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« Reply #9 on: January 14, 2017, 06:41:22 AM »

Quote
VK is probably different to you guys, but at HF frequencies with a vertical 1000 watts would be fine in terms of exposure so long as you are a good 20-30 ft from the antenna

The FCC requirements for analysis are more prescriptive and are required to be done at these power levels.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W2BLC
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« Reply #10 on: January 14, 2017, 06:57:52 AM »

1. The SB200 is too old - worn wafer switches and other stuff are showing their age.
2. You can get the AL811 with 572B tubes - makes it a little stronger. No increase of power.
3. Dipoles up to 50% size reduced with coil loading work well - just are narrow banded.
4. I now have a solid state amp, due to the reduced size and weight. Puts out 500 Watts.
5. First 500 Watts is the most important. I have found no times when I cannot make contacts.
6. More powerful amp requires bigger size, increased weight, and probably tuning (tube type).
7. If you can stand the size and need for tuning, then a tube amp will do more for you cheaper than solid state.
8. Voltages in a tube amp can kill you!
9. House wiring must be able to support an amp. A 220 dedicated 20 amp line is recommended.
10. Plugging into the wall plug 110 won't do much except cause modulated lamps.
11. Improve the antenna situation before putting an amp in. Much cheaper than an amp.

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KB1SNJ
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« Reply #11 on: January 14, 2017, 07:17:43 AM »

all great info thanks.     the base of my vertical is 10-12ft from where I sit inside the house, and on the fence line. If I use a shorter vertical, and assuming I can not radiate from the feedline, it could start higher, above the roof and away from the property edge. (see pic).  as someone who has not operated an linear amplifier, i appreciate the advice. such as the SB200 idea, and that the first 500 watts gets the most bang for the buck. A quick check on fleabay shows sb200's going for 300-500 generally, often near the top of that range. how do those sound? why is it 'MUCH better' than AL811? in what way?

thanks for all the info

Here is my small lot property layout:  https://flic.kr/p/QZj9r9



« Last Edit: January 14, 2017, 07:28:51 AM by CHRISDX » Logged
N8FVJ
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« Reply #12 on: January 14, 2017, 07:31:56 AM »

Two amps come to mind. Ameritron AL-811 with three 811A tubes or Heathkit SB-200 with Harbach upgrades. 500 watts out from the Ameritron AL-811 and 600 watts from the Heathkit.

You can retrofit Chinese 572Bs in the Ameritron three tube AL- 811. The three tuber Ameritron shares the same power transformer of the four tube AL-811H Ameritron, thus you can get 600 watts out of the Ameritron 811A with three 572Bs. The Chinese tubes have proven to be reliable.
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W8JX
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« Reply #13 on: January 14, 2017, 07:53:54 AM »

The SB200 is too old - worn wafer switches and other stuff are showing their age.

If this was really true all SB200's and 201's would be in junk pile but they are not. (neither are SB220's of same age) I own a SB200 and it is still nice and tight. Quality of switchs when new was much better than what is used is a AL811

You can get the AL811 with 572B tubes - makes it a little stronger. No increase of power.

Not quite true. While you can swap in 572's you do not need as many and you can increase power because you can safely run a 50% higher plate current. 3 572's can handle more power than a AL811 power supply can make and while safely make more power than 4 811's (putting 4 ea 572's in a AL811H is a waste of money as 3 will make just as much power as power supply cannot begin to exploit 4 of them as 811H use exact same power supply as base 811)  You could even try 2 ea 572 in a AL 811 and use same current setting as in manual as two 572's can handle more than 3 811's and still have over twice the safe dissipation as 3 ea  811's and should be able to get 450 watts or so. (I mention this to show what a weak amp tube a 811 truely is. Nothing remotely HD about it)  Furthermore when compared to a SB 200 the 200 has 50% higher plate voltage than AL811 and can use 572's far more efficiently. Also same money spent to retube a AL 811 a few times or upgrade to 572's will easily buy a used AL80 (a real amp). AL 811 look cheap to buy but when you factor in tube replacements it is not (just like inkjet printer look cheap but you pay a lot for ink for it)

I now have a solid state amp, due to the reduced size and weight. Puts out 500 Watts.

SS amps are not as rugged or forgiving and require very low SWR. A tube amp can run with 2 to1 or so SWR without any concern

First 500 Watts is the most important. I have found no times when I cannot make contacts.

 I say first 600 to 800 watts mean most for a few reasons. First 600 watts is a little over 6 db (one S-unit) and 800 watts is 9 db (1 1/2 S-units). Going from 800 to legal limit (though many go way beyond that today) is abt 3 db and not a big deal (and this is way many quietly run far more power)

If you can stand the size and need for tuning, then a tube amp will do more for you cheaper than solid state.

In bang for buck and ruggedness you cannot beat a tube amp (except overrated POS 811 amp which should be avoided)

Voltages in a tube amp can kill you!

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

House wiring must be able to support an amp. A 220 dedicated 20 amp line is recommended.

Not really, I have used a 15 amp 240 volt circuit feed with 14/3 for over 20 years and never had a problem. It will easily feed a legal limit amp and 14 ga is a bit easier to route in tight places too. (you do not really need a 20 amp circuit unless you plan to regularly exceed legal limit by a good bit)

Plugging into the wall plug 110 won't do much except cause modulated lamps.

It depends on size of amp. A SB200 plays nicely on 120 but if you get a AL80B and plan to run it hard you want a stiff 120 volt circuit. Also you have to look at total draw on circuit. If you are using a old technology linear supply you wil draw close to 500 watts (a bit over 4 amps) from wall to power a SS rig at 100 watts due to efficiency losses. Use a switching power supply and peak draw for rig from wall will be close to 3 amps and every little bit helps with a amp on a 120 volt circuit

Improve the antenna situation before putting an amp in. Much cheaper than an amp.

True but not easy to get 6 to 9 db on HF with a new antenna unless other one is very bad.
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KB4MNG
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« Reply #14 on: January 14, 2017, 08:54:34 AM »

IMO the best amp on the market is the al 80 b. Simple design, one tube that is easily obtainable and priced fairly, and a great company. Yeah, there are other amps that are much better but they are expensive and complicated. If you have a solid state radio, I would really consider the als 600, also another great amp for the same reasons. I have both.

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.

There are some heathkit models that employ the 3-500 tube that are really good if you can get them at a good price. It may require some repair or maintenance.
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