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Author Topic: Thinking of buying an amp.  (Read 2667 times)
N4ZYV
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Posts: 90




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« on: September 28, 2003, 07:52:19 PM »

I've been contemplating the purchase of an amplifier. I've read through several threads here and have a few questions.

I've been reading that I should probably steer clear of the older amps due to aging components. Also, there is the problem of obsolete tubes. I understand that I should also stay away from amps that use sweep tubes in various numbers.

So, what amps to avoid? I just don't know what amps use what tubes.

What brands have distinguished themselves by being lousy amps?

I see Heathkit amps for cheap, Dentrons, Swans. Any of them really stand out as better than the others? Even within the same brand?

I have read some about Ameritrons and they seem to enjoy a good reputation. How about Aplha?

Opinions requested.

Thanks.
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KA9CCH
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Posts: 87




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« Reply #1 on: September 28, 2003, 09:48:36 PM »

Try this intresting article
http://www.eham.net/articles/3722
has a good description of many popular amps.

You are right to avoid sweep and other obsolete tubes, hard to find at a reasonable price.
I purchased an amp on e-bay,  good price (takes patience and will power to stay within a limit) and local pickup.

Good luck
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W8JI
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« Reply #2 on: September 28, 2003, 10:11:39 PM »

I have some technical info about tubes and tube failures on my web site www.w8ji.com/amplifiers

All low and medium power tubes are going obsolete. Eimac dumped the glass tube line several years ago, and Svetlana was actually selling new-old-stock glass tubes like the lousy 572B's they sold.

Your only choice now is to buy glass tubes from limited vendors. Eimac makes smaller ceramic tubes still, and there are many surplus Russian tubes, but the real source where tubes are being manufactured now is mostly China.

Richardsons Electronics, who almost single handedly ruined the tube market for Hams, owns Amperex and they still manufacture 3-500Z's in France.

It looks like your choice is to use Russian Tetrodes or surplus triodes, which may or may not be around for a while, Eimac ceramic triodes, or glass tubes from offshore.

Myself, I'd stay away from tetrodes. They not only have higher splatter, they are touchier to tune. You also can not easily substitute another tube in a tetrode amp, like you can in a trode GG amplifier.

All of my amplifiers (I have about 15 of em) are triode tube type amps, except for solid state ones. You just have to shop around and see what you like.

Stay away from Swans and old Heathkits. Stick with something newer if you can afford it. Simple amps like grounded grid amps are more reliable, and easier to repair.

73 Tom
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WB2WIK
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« Reply #3 on: September 29, 2003, 11:35:13 AM »

I certainly second Tom's remarks.

Added food for thought: As an engineer and long-time tinkerer/homebrewer, I enjoy a lot of the old amps but truly consider them to be long-term projects.  I've painstakingly restored many old amps from Johnson Thunderbolts to BTI 3-1000Z units, to Swan Mark 1's, to the old, original Dentron products -- and some older than any of these.  But when buying an older amp I always assume there's something wrong with it, and that I'll need to invest 20-30-40 hours or more into it...in some cases, a lot more.

I would *never* buy such an item sight-unseen from an eBay (or otherwise) seller.  If you find a "deal" on eBay, great -- but make it a local deal, so you can drive over and inspect the goods.

For new goods, Ameritron products do offer a lot of bang for the buck.  I have a homebrew 4-1000A amp I built in 1984 which runs 1500W output with only about 30W drive (it's grounded cathode, driven grid with tuned input and has a lot of gain) without breathing hard, but since I purchased a little desktop AL80B, which runs just about 1 kW noiselessly, I find myself using the "little" amp all the time, and don't even turn on the "big vacuum cleaner" (4-1000A) unit, which is noisy and blows the dust around the room.  For an extra 1.76 dB, it's not worth it -- plus, the big amp takes two minutes to warm up, and the little one takes three seconds!

WB2WIK/6

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K5XOR
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« Reply #4 on: September 30, 2003, 01:33:27 AM »

You didn't specify if you wanted a tube over a solid state. IMHO, if it's your first amp you are probably better off sticking with a recent solid state amplifier with about 500w of power. Personally I own an Icom IC-2KL solid state 500w amp and it works very well and was had for a reasonable price. Combined with my Icom rig and tuner it is easy to use, quiet, and doesn't require on-air tuneups that are annoying to people on the band. I suspect most other manufacturer's solid state designs work equally as well with their respective radios.

In my situation I own a vertical antenna and I've never had a situation arise where I needed more than 500w for the receiving station to hear me or to break reasonable pile-ups. Lastly, I've found that most modern solid state amps from the reputable radio manufacturers (Yaesu, Icom, etc.) rarely suffer from bad build quality.

All-in-all I only use the amp for very noisy conditions or if I want to ensure the signal makes it through. I'd say that 98% of my time I'm running barefoot at 100w with few issues. We'll see how that figures holds up now that the sunspot cycle is on the decline. Smiley
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N4ZYV
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Posts: 90




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« Reply #5 on: September 30, 2003, 08:10:50 PM »

Well, I was thinking about a tube amp. The big power supply needed for a solid state amp would realy drive the price up where I would start to cry as I wrote the check.

I was thinking around 500-800 watts for power. there's a hamfest coming up in St.Paul Mn. this Oct 25 and I thought I would look for something there. See what the prices are like.

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W1DY
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Posts: 29




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« Reply #6 on: September 30, 2003, 11:17:11 PM »

My Husband Just bought me my first amp...
An Ameritron AL-80B.

I had been running barefoot out of my Yaesu FT-990 for years.

It was a TOTAL Suprise when this Huge box arrived!

About 2 weeks later an Ameritron ATR-15 antenna tuner also found it's way to our door!

Let me tell you...it has been quite a learning experiance!..
But...If I knew then What I know now...!!

This has totally opened up a new world of DX for me!
I am completely sold on Ameritron products...But as this is my first amp..I am also COMPLETELY biased!

Sure I'd love to buy a new QRO amp....but I'd like to hit the lottery too!

All I can say is that I LOVE Mine..
I don't think you could go wrong with one as well!

Good Luck...and trust me...make the plunge..you'll never look back !

Wendy
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KD5VHF
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Posts: 84




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« Reply #7 on: October 01, 2003, 10:33:14 AM »

How is your antenna system? Is it the absolute best it can be(within your limits)? If the answer is yes and you are still having problems, then a amp would be the next step.
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W4ILT
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Posts: 5




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« Reply #8 on: October 01, 2003, 04:03:02 PM »

Recently received a Tokyo Hy-Power HL-1KFX solid state amplifier that I ordered direct from THP and I have been thrilled with the construction and preformance of this amp. 300 to 400 watts makes the difference between being heard and the common----you are just at my noise level.


Good luck on your decision!

73,

Wayne
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N4ZYV
Member

Posts: 90




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« Reply #9 on: October 01, 2003, 11:42:48 PM »

Well Mike, my antenna is non-existant right now. I'm just now getting back into HF after being mostly out of the hobby. I know that with my very small lot, any antenna is going to be less than ideal. I also live in a valley surrounded by bluffs.

I don't even have a decent radio yet. Just an old Swan 400 for now. I'm going to be purchasing equipment this fall and wanted to get a better idea of which way to go with the amp. I've learned a lot by reading through the other threads in this forum and from advice given to my questions.

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W7VP
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Posts: 26




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« Reply #10 on: October 02, 2003, 07:29:33 PM »

I have to agree with some and not with others on this thread.  I love my Ameritron AL 800 amp, even though it takes more than 3 minutes to warm up.  Still I love my 4-1000A even more.  It is the second one I have had and It seems to get better with age.

Mind you, though, I am not a grounded grid fan.  Most of them do not operate in the linear part of the transfer characteristic and thus are subject to a lot of distortion.  I converted mine to class AB2 with 4000 vdc on the plate, 500 vdc on the screen and -67 vdc on the control grid.  Drive is through a 4:1 balun terminated with 200 non-reactive ohms and fed to the control grid.  As one of the other replies stated, you get a lot of gain.  I get more than 1200 watts out of a relatively new tube for less than 50 watts in, most of which is being sunk in the balun resistor.

Still I only use it on 20 and use the other amp on all the other bankd.

So you may be able to find a decent old amp out there but you will very likely need to redo it to make it clean enough for today's conditions.

73's
Bill
W7VP
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WB4M
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Posts: 124




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« Reply #11 on: October 05, 2003, 11:02:46 PM »

The best reply so far.  Spend the money on your antenna system first.  An amplifer is useless on receive.
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NI0C
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Posts: 2433




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« Reply #12 on: October 08, 2003, 04:43:08 PM »

I wonder if anyone else caught W1DY's pun above: "completely biased."  That was a good one!

Cheers,
Chuck  NI0C
 
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W5ZZG
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Posts: 7




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« Reply #13 on: October 12, 2003, 12:04:15 AM »

I too am looking for an Amp.  The problem that I have is that I have no access to a good ground or anything that I could use as a ground.  Anyone know anything about MFJ's artificial ground "box" and if it might work with any kind of power?  

I wonder if I had a "500" watt amp and then used it with a ballanced type antenna.... Could I get away without a ground?  Any ideas on this?

Regards, Jim
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K7KBN
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Posts: 2835




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« Reply #14 on: October 12, 2003, 08:17:13 PM »

The MFJ 'Artificial Ground' is not designed for use with a coax-fed antenna.  I've tried mine just to see if there's any difference with it, and there isn't.  However, on a random wire, or just about anything fed with a single wire or open line, it does improve the amount of signal radiated.  All cases will be different, but with a 475-foot, end-fed wire over some pretty dry desert soil, the MFJ consistently gave me a better indication of good power forward, and 2-3 s-units improvement on the other end.  This was a few years back, right after the MFJ Artificial Ground first hit the market.
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73
Pat K7KBN
CWO4 USNR Ret.
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