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Author Topic: How to choose a linear.....  (Read 7987 times)
KB8BAB
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Posts: 101




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« on: July 22, 2012, 06:42:37 PM »

Probably a loaded question....

In the near future I'll be looking to upgrade with a linear of some sort. There are a few choices out there. I'm looking for something in the perhaps 800 to 1KW range.
Solid state for me is out of the question (and budget) so it would become a tube amp, which quite honestly I have "zilch" knowledge about. (but willing to learn)
I also have no intention on driving the amp (whatever I get) at 100%,but rather let it "loaf" (to speak) at 70 or 80% which should help the longevity.
The question is new or used...

The "old" (used)...
Looking at the classifieds and flea-bay, I can find Collins 30L-1 (1200W PEP Input?), Heathkit SB200 (1200W PEP Input?) Heathkit SB220/221 (2KW PEP Input?).These seem to be the favorites...
Prices ranging from $300 up to $800 (sometimes more). Now these are amps in various conditions, but regardless, the technologies in these are ~30 yrs old.
Some have tubes that are "relatively" cheap to replace, others are more expensive.
However in all the material I have read thus far, it is obvious that the tube life depends on the use or abuse that the amp has seen.

The "new"....
Within my budget ($1500 max), I see the Ameritron line...(are there others?).
Are the newer amps better in their design (technologie)? Does this make them more reliable? Improved signal quality?

Regards, Bart





 
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N3JBH
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« Reply #1 on: July 22, 2012, 07:06:30 PM »

I say the AL 80B is best bet.... Unless you know  how to look over and update the older amp's. I stay way from the Collins and SB 200
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K7MH
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Posts: 339




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« Reply #2 on: July 22, 2012, 07:11:41 PM »

There are several factors to consider.
If used can you repair it?
Availability and reliability of tubes or semiconductors and replacement cost.
WARC bands can be used with it or do you care about that?
Does it have a tuned input? Do you need one?
Budget is of course a concern.
Do you have a 240V outlet you can use or get one wired for higher power amps?
Or would you rather have a lower power amp that runs ok on 120Vac?
Do you want QSK?

One big question is do you have good antennas already?
They are always a more worthwhile investment.
You can't work what you can't hear.

The Ameritron AL-80B is usually considered the best bang for buck amp out there.
I have had a Clipperton L, a Henry 2KD4, an AL-1200 I never even fired up in about 4 years and sold, and an AL-811 that I regularly use for several years now. I got them all used from the same person a friend of mine...good salesman I guess!!
IF I were to buy another amp, it would be an AL-80B.
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W8JX
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« Reply #3 on: July 22, 2012, 07:18:36 PM »

I say the AL 80B is best bet.... Unless you know  how to look over and update the older amp's. I stay way from the Collins and SB 200

AL-80B is a good amp but nothing wrong with SB-200 either. Well built amp and still a solid performer and easy to rebuild/repair. Many of them 40+ years old are still in use today which is testimony to their design and reliability. Stay away from AL 811 amps.
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N3JBH
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« Reply #4 on: July 22, 2012, 07:25:07 PM »

I say the AL 80B is best bet.... Unless you know  how to look over and update the older amp's. I stay way from the Collins and SB 200

AL-80B is a good amp but nothing wrong with SB-200 either. Well built amp and still a solid performer and easy to rebuild/repair. Many of them 40+ years old are still in use today which is testimony to their design and reliability. Stay away from AL 811 amps.


I was was primarily concerned about the quality of replacement tubes. That was the reasoning behind the two amp's i did not seem to recommend was all
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N4CR
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Posts: 1672




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« Reply #5 on: July 22, 2012, 09:41:10 PM »

In 'Real' S units, there is 1/2 S unit difference between 800 watts and 1500 watts. So to get to full legal limit, you spend a lot more money and get a lot less for it. And you'll need 220 volts wired up to get to full legal limit.

Remember, you don't run a linear for you, you run it for the other guy. He won't be able to hear the difference.

I'd recommend a new AL-811H. Run it around 650 watts and it will last forever. Replacement tube sets are $140 and still being manufactured. If you want a bulletproof one, get the one that has 572B's in it, the AL-811HD. It's got grid current protection built in so it's going to be about impossible to hurt it.

But before you do the amplifier thing, have you made sure your audio is top notch and gotten up a great antenna? Either of those can trump an amplifier if what you have now is inadequate.

I like the W2IHY EQplus with any good ball microphone on a boom for audio.

I have up a Cushcraft R-8 and I've gotten 125 DX entities confirmed since last July with 650 watts or less.

What are you trying to accomplish? That may well dictate the choices.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
ZENKI
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Posts: 960




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« Reply #6 on: July 23, 2012, 03:21:54 AM »

Dont forget the IMD performance of the amplifier. This is one aspect of a amplifiers technical performance that everyone ignores.

Its disturbing that so many hams are now deciding to use CB amplifiers without considering the impact that these poor designs have on the ham bands. The IMD performance and design class of these amplifiers
must rank as the worst decision a ham can make in his or her equipment choice. They certainly cause  a lot of splatter and interference.

I would always choose a  triode amplifier over any  hard to obtain Russian Tetrode amplifiers. Tubes such as the 3-500. 572b's, 3cx800s and 8877's are  far superior to the Russian Tetrodes in IMD performance.
Tetrode amplifiers are also not the ideal design if you are new to using  a high power amplifier.

 Because of the typical poor transceiver ALC designs which cause power overshoots, most modern ham radio transceivers  when matched with a
tetrode amplifier cause a lot of unnecessary interference in adjacent frequencies. Tetrodes are very sensitive to power spikes and mistuning which results in the splatter..
Tetrodes are also a lot harder to tune because mistuning and causing  a lot of splatter can be easily done even by experienced operators. These days its easy spotting stations using tetrodes because
they have a characteristic splatter signature. The are great at causing leading edge splatter that is very wide.

If I wanted the cleanest signal I would always choose a triode amplifier design.  The prices being asked for Russian Tubes dont make them a bargain anymore and you certainly get less IMD performance.

How clean and by how much  any amplifier splatters should be a major concern for any ham considering buying a new amplifier.


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WX7G
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Posts: 6134




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« Reply #7 on: July 23, 2012, 06:13:27 AM »

Running the amp at 70% only will do nothing to reduce tube plate dissipation if tuned by the manual. That is, if you tune for rated maximum power by peaking LOAD and PLATE it will achieve maximum efficiency at full power and of course reduced efficiency at reduced power. Linear amplifiers are "efficiency" modulated.

Now if you tune for 70% of rated power by peaking LOAD and PLATE (and reducing input power) plate dissipation will be reduced but linearity may suffer. What to do? Run the amp as it was designed to be run. Full rated power and tuned by the book.

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W4VR
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« Reply #8 on: July 23, 2012, 01:30:43 PM »

The AL-80B is not a bad choice if you can find one that was assembled correctly.  MFJ has had quality control problems, but I understand they are doing something to improve that.  You can buy an ALS-600 for the same price, but you won't get quite as much power out as you will with the 80B.  I had the ALS-600 for a couple of years and never had a problem with it at 500 watts output.  If you have an external tuner a solid state amp is the way to go.  Whatever you do, buy something new so you won't have to replace the tubes right away.  There are lots of folks out there that are very hard on amplifier tubes, trying to squeeze out that last watt.
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KB8BAB
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Posts: 101




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« Reply #9 on: July 23, 2012, 02:23:41 PM »

Thanks guys...
Some very use-full info.
Answer to some questions posted.

- Supply power: I have 110 but could relatively easily get 220V in the shack.
- Antenna OK? (Good?): Well I have a Hygain 14 w/40mtr kit at about 45ft and a Solarcon stick on top of that. Have a GRV5 as well just not put up yet.
- What do I want to do?: Rag-chewing with others from anywhere, I've also been listening to the mail on the other bands (still a techie here) but am beginning to like the DX-ing as well.

Consensus here seems to lean towards the newer amps AL-80B or AL-811H (or HD version)......
Yes I guess I'm kind-off putting the "Cart before the Horse"....but I'm having fun building my station...next is the step up to the General class...

73's everyone...

Bart
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N4CR
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Posts: 1672




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« Reply #10 on: July 23, 2012, 02:59:21 PM »

- Antenna OK? (Good?): Well I have a Hygain 14 w/40mtr kit at about 45ft and a Solarcon stick on top of that. Have a GRV5 as well just not put up yet.

What kind of radials do you have on the 14AVQ ?

Your G5RV is a good 20 meter antenna that works passably on a few other bands, but it's only a good performer on 20 and not a stellar performer anywhere else.

Quote
- What do I want to do?: Rag-chewing with others from anywhere, I've also been listening to the mail on the other bands (still a techie here) but am beginning to like the DX-ing as well.

If you want to rag chew you'll probably want to be on 75 meters at night. If that's the case, then you'll want to put up a 75 meter dipole. I prefer one fed with ladder line but that's a choice you'll have to make.

For DX, you'll not find many rag chewers. Many of them are English language challenged enough that giving contact information is the limit of their capability.

When you do find a DX station willing to rag chew, you may want to gnaw your microphone cord in two before it's over. They can be long winded.

Quote
Consensus here seems to lean towards the newer amps AL-80B or AL-811H (or HD version)

You'd be happy with either of them. DX generally depends on conditions, operator savvy and timing. Very seldom is power the one thing that makes it happen. When conditions are right you'll eventually break through the pileups if you keep trying. Without conditions, you might as well find someone local to rag chew with.

Quote
Yes I guess I'm kind-off putting the "Cart before the Horse"....but I'm having fun building my station...next is the step up to the General class...

Bart, it's great that you have big plans and aspirations. Don't let anyone stop you.

Now, go pass your general license and get going!
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
KB8BAB
Member

Posts: 101




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« Reply #11 on: July 23, 2012, 03:17:40 PM »

- Antenna OK? (Good?): Well I have a Hygain 14 w/40mtr kit at about 45ft and a Solarcon stick on top of that. Have a GRV5 as well just not put up yet.

What kind of radials do you have on the 14AVQ ?

None actually....I should have written it as a Hygain Explorer 14...sorry.
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W8JX
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Posts: 6060




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« Reply #12 on: July 23, 2012, 03:28:21 PM »


Consensus here seems to lean towards the newer amps AL-80B or AL-811H (or HD version)......
Yes I guess I'm kind-off putting the "Cart before the Horse"....but I'm having fun building my station...next is the step up to the General class...


The 811HD is a waste of money. Nothing HD about it. It uses same power supply as 3 tube amp. It would offer no real advantage over a 3 tube version retubed with 572's as power supply is LD in it and cannot begin to exploit 572's. If you look at a 811h and 80b with cover off, the 80b has about twice the transformer mass and its single tube has over 2x the continuous rated plate dissipation as four 811's combined. Which one do you think is the true 800 watt amp?
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N4CR
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« Reply #13 on: July 23, 2012, 07:12:10 PM »

The 811HD is a waste of money. Nothing HD about it. It uses same power supply as 3 tube amp. It would offer no real advantage over a 3 tube version retubed with 572's as power supply is LD in it and cannot begin to exploit 572's. If you look at a 811h and 80b with cover off, the 80b has about twice the transformer mass and its single tube has over 2x the continuous rated plate dissipation as four 811's combined. Which one do you think is the true 800 watt amp?

First you talk about an 811HD not being heavier duty and then you say how a 811H doesn't match up. Seems like apples and oranges to me.

1. There is a grid protection circuit in place in the HD to prevent overdrive and over current. This protects the grids, not the plates which don't need protecting on 572b tubes in this lower voltage application.

2. It has a heavier duty tank circuit and can do 600 watts RTTY. This would melt the tubes in an 811H. The AL-80B is rated 500 watts RTTY.

3. The fact that the 811 uses the same transformer as the 811H doesn't mean the 811H transformer is inadequate. It means they save money by sourcing and stocking a single transformer that is more than good enough for the smaller 811 3 tube amp.

4. The 811H(D) amplifiers are able to do 600 watts continuous and 800 icas SSB. I've measured it personally. The power supply exploits a 572b exactly the same as it exploits an 811. They didn't claim it outputs more power. Both tubes have the same gain at the same voltage. But you'll have a hard time hurting the 572b's in this application. They will virtually last forever even when run maxed out all the time. The three tube amp with 572's won't quite do this. I've measured it and they don't.

5. 4 x 572b's have more plate dissipation capability than 1 3-500z. The fact that 811a's don't is a red herring here since that's not the tube that's installed.

If you think it's a waste of money, that's your opinion, but there's no reason to obfuscate the facts with mixed references.

With that said, the AL-80B is probably their best selling amp ever and their tech support claims it has the least warranty claims of all amplifiers they sell. That's a very good recommendation. But lets stick to the facts here.
« Last Edit: July 23, 2012, 07:25:59 PM by N4CR » Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
W8JX
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Posts: 6060




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« Reply #14 on: July 23, 2012, 07:45:07 PM »

First you talk about an 811HD not being heavier duty and then you say how a 811H doesn't match up. Seems like apples and oranges to me.

A 811H was created as a after fact after 3 tube one. Same power supply nothing HD here. MD at very best.

1. There is a grid protection circuit in place in the HD to prevent overdrive and over current. This protects the grids, not the plates which don't need protecting on 572b tubes in this lower voltage application.

Chances of over driving/damaging the grids of four 572's in parallel with 100 watts are pretty slim. Nice window dressing though.

2. It has a heavier duty tank circuit and can do 600 watts RTTY. This would melt the tubes in an 811H. The AL-80B is rated 500 watts RTTY.

Not sure how they come up with this number. 80b has a much bigger power supply. 600 watts out on 811HD would put about a 1kw load on smallish power transformer and would heat it up quickly.

3. The fact that the 811 uses the same transformer as the 811H doesn't mean the 811H transformer is inadequate. It means they save money by sourcing and stocking a single transformer that is more than good enough for the smaller 811 3 tube amp.

You got it backwards. 3 tube came first and then they simply added another tube and socket and used same power supply to cut costs.

4. The 811H(D) amplifiers are able to do 600 watts continuous and 800 icas SSB. I've measured it personally. The power supply exploits a 572b exactly the same as it exploits an 811. They didn't claim it outputs more power. Both tubes have the same gain at the same voltage. But you'll have a hard time hurting the 572b's in this application. They will virtually last forever even when run maxed out all the time. The three tube amp with 572's won't quite do this. I've measured it and they don't.

Exploit is not the word use for 572's in a 811 amp. Under utilize is a much better term. There is a good chance that tubes will never get warm enough to properly getter and fail due to gas sooner than they should.   I have a 28 year old Dentron Clipperton QRO with 4 - 572's and it will do 1000 watts all day long with 55 watts of drive on SSB and more if you push it and tubes are 20+ years old. It has the power supply to properly utilize 572's

5. 4 x 572b's have more plate dissipation capability than 1 3-500z. The fact that 811a's don't is a red herring here since that's not the tube that's installed.
 

stock cooling is lacking on that amp to really use the rated capacity of the 572's

If you think it's a waste of money, that's your opinion, but there's no reason to obfuscate the facts with mixed references.

Not sugar coating anything here.

With that said, the AL-80B is probably their best selling amp ever and their tech support claims it has the least warranty claims of all amplifiers they sell. That's a very good recommendation. But lets stick to the facts here.

I have
« Last Edit: July 23, 2012, 07:47:23 PM by W8JX » Logged

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