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Author Topic: Choosing a Legal Limit Amp  (Read 16894 times)
W6UV
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Posts: 536




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« on: April 14, 2013, 09:49:33 PM »

I'm ready to buy a legal limit amp and have narrowed my choices down to a few. I want something closer to the high-end rather than the low end, so my list doesn't include any Ameritrons.

Prime considerations are durability and availability of tubes/transistors in the future. Here's my list, ordered by preference:

1. Alpha 8410. Alpha is a U.S. company with a very good reputation for building robust, quality products. For almost my entire ham career of 33 years, Alpha has been one of the gold standards. I see only two shortcomings with this amp -- the 4CX1000A tubes may become hard to get in the future, and the use of a microcontroller in the protection circuits may make this amp impossible to repair in the future if the microcontroller (or other components) are not available. Alpha has an excellent reputation for service and support.

2. Tokyo Hy-Power HL-2.5Kfx. SS amp that doesn't need tuning. All of my antennas have SWR < 1.5:1 where I operate, so I won't need an antenna tuner to keep this amp happy (for now). About $600 more than the Alpha 8410. Prime concerns with this amp are the availability of the ARF-1500 MOSFETS in the future and the availability of service since the company is in Japan. Another consideration is RTTY output is only 1KW with a 5 minute limit (I do RTTY contesting) -- the Alpha 8410 is brick-on-the-key 1.5KW all modes with no time limit.

3. Other tube amp, such as an Acom 1500 or Emtron DX-2SP. Concerns are with tube availability (FU-728F for the Emtron and 4CX1000A for the Acom) and support from Bulgaria or Australia.

Opinions on this list? Anything else I should consider?
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K2DC
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« Reply #1 on: April 15, 2013, 03:10:04 AM »

The obsolescence issues you raise are true of any amplifier (or any other peice of electronic equipment), regardless of whether it's a tube or SS amp.  It's interesting that you didn't raise the microprocessor availability issue with the THP, as it has similar protection circuits.

Of your two prime candidates, I would definitely go with the Alpha.  Although bought used, I have a 78 and an 86 that have given me years of great service.  4CX1000's are readily available and reasonably priced compared to other higher power amatur amp tubes.  Given Alpha's known design and build quality and a set of spares, a new 8410 could easily outlive us all.

73,

Don, K2DC
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AD4U
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Posts: 2151




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« Reply #2 on: April 15, 2013, 05:40:33 AM »

Another option is trying to find a good used Alpha 77DX which will actually cost less than most if not all of the amps you mentioned.  Of course the 77DX is manual tune, which will (but should not) baffle some ops.  It covers 160 meters and 3-30 MHz continuous.  The HV filter cap is oil filled and should last a life time.  It will LOAF at the legal limit in ANY mode.  EIMAC 8877 tubes are still available. But then if you get an amp with a good EIMAC 8877 and if you don't abuse it, it will probably last a life time.  

It is probably the best HAM amp ever made.

Dick  AD4U
« Last Edit: April 15, 2013, 06:11:33 AM by AD4U » Logged
W6GX
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Posts: 2307




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« Reply #3 on: April 15, 2013, 04:53:59 PM »

You didn't mention warm up time.  That three minutes may seem like eternity when a rare one is one the line.  Personally I prefer the 2.5 due to the no-tuning and no warm up time.  OTOH I don't do RTTY contesting so I'm not concerned with duty cycle.  For my operating style the 2.5 is a better choice.  If I were you I wouldn't want to run more than 1kw on high-duty RTTY into a trapped antenna.  The traps might be the limiting factor, not the amplifier.

Neither amps could do 6m.  That might be an important consideration if you are into VHF DX'ing.

73,
Jonathan W6GX
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K5RT
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Posts: 122




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« Reply #4 on: April 15, 2013, 07:04:43 PM »

Check out the OM-2500A. It's definitely a high end legal limit amp
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W6UV
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Posts: 536




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« Reply #5 on: April 15, 2013, 09:41:47 PM »

You didn't mention warm up time.  That three minutes may seem like eternity when a rare one is one the line.  Personally I prefer the 2.5 due to the no-tuning and no warm up time.  OTOH I don't do RTTY contesting so I'm not concerned with duty cycle.  For my operating style the 2.5 is a better choice.  If I were you I wouldn't want to run more than 1kw on high-duty RTTY into a trapped antenna.  The traps might be the limiting factor, not the amplifier.

Warm-up time is not much of a consideration, since I power up everything as soon as I go into the shack and the computer takes at least three minutes to boot and load everything. I don't do any operating until the computer is ready.

I'll look into the trap issue on RTTY -- didn't think about that. Worst-case RTTY contesting duty cycle is about 80% when calling CQ and getting no answers. With the traps up in the always prevailing breeze around here, there is some cooling that they'll get. Besides, if I blow the traps, that'll give me an excuse to try a different antenna. Cheesy
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N0PQK
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« Reply #6 on: April 15, 2013, 10:00:24 PM »

QRO Technologies makes some rock solid tube amps. You may want to look into one.
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W6UV
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Posts: 536




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« Reply #7 on: April 15, 2013, 10:47:56 PM »

QRO Technologies makes some rock solid tube amps. You may want to look into one.

Hmmmm. The HF-3KDX looks pretty interesting. How would it compare with the Alpha 8410?
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N4ATS
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Posts: 798




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« Reply #8 on: April 16, 2013, 03:59:44 AM »

Alpha all the way , there is NOTHING better. You can get a great price on an Alpha 89 right now , older amp with a new style that packs it all. Indestructible and 1.5 KW all day long.
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KH6DC
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Posts: 634




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« Reply #9 on: April 16, 2013, 10:00:00 PM »

The obsolescence issues you raise are true of any amplifier (or any other peice of electronic equipment), regardless of whether it's a tube or SS amp.  It's interesting that you didn't raise the microprocessor availability issue with the THP, as it has similar protection circuits.

Of your two prime candidates, I would definitely go with the Alpha.  Although bought used, I have a 78 and an 86 that have given me years of great service.  4CX1000's are readily available and reasonably priced compared to other higher power amatur amp tubes.  Given Alpha's known design and build quality and a set of spares, a new 8410 could easily outlive us all.

73,

Don, K2DC


I second the Alpha or Tokyo Hy-Power.  But another one you might take a look is SPE Expert.

73,

Delwyn, KH6DC
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73 and Aloha,
de Delwyn, KH6DC
NO9E
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Posts: 382




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« Reply #10 on: April 17, 2013, 07:12:36 AM »

The choice depends on criteria.

1. Cost. Lowest? Good value? The best that there is?
2. Value of automation.
3. Willingness for risk taking.
4. Needed headroom.

Lowest cost with good value would be AL-1500. Alpha 8410 would extra higher quality. ACOM 2000 and Alpha 9500 seem both highly rated automated amps. OM3500 would add extra headroom. Expert 2k-fa would provide the highest level of convenience ( 6 automatically switched and tuned antennas to 2 radios) but with uncertain (but seemingly very high) reliability and less headroom while covering legal-limit 6m.   

I chose 2k-fa.

Ignacy

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W6UV
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Posts: 536




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« Reply #11 on: April 17, 2013, 09:00:11 AM »

As always, one has a budget for such things. In my case, the Alpha 8410 is comfortably within my budget. The Tokyo HL-2.5Kfx is stretching it to the limit, but doable. The Alpha 9500 is outside my budget, as is the Acom 2000A and OM3500.
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PA1ZP
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Posts: 203




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« Reply #12 on: April 17, 2013, 09:05:28 AM »

Hi All of you

Why not the Acom 2000?
Acom used to build amps for Alpha.

I hear great things of this amp.

maybe in the chaep range the AL82 with 2 x 3-500

I am using a AL572B and that produces more then 2 times legal limit in the Netherlands.
I do not use it much but I put in a new set of tubes 3 yrs ago and besides a set of warn tubes I had not trouble in 6 yrs of service.

Now I only put out between 400-500 PEP watts and that is enough though my antenna system for 10-40 mtrs can cope with 5 Kw PEP.

I used to use the AL572B daily but last few years only about 2 times a week for  few hours.
It does the job I needed it to do very good.

I never use it on CW because strange enough sigs on CW are always strong enough, so I can do without the amp.
A set of 4 new 572B tubes from China costed me 140 Euro's about  $200   

73 Jos
« Last Edit: April 17, 2013, 09:13:54 AM by PA1ZP » Logged
W6GX
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Posts: 2307




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« Reply #13 on: April 17, 2013, 10:46:16 AM »

If you are still interested in the HL-2.5kfx I want you to be aware of some new developments in regards to this amp.

- HL-2.5kfx will be replaced by HL-2500kfx.  I don't know the timing but Tom Rum (US rep. for THP) should know.  There's nothing wrong with the HL-2.5kfx other than the ARF-1500 won't do 6m.  THP felt that there's a demand for an amp. that will do 160-6m.  The HL-2500kfx uses six THP2933 PAs.  THP2933 is a custom and rugged version of the ST Micro SD2933.  You should expect a price increase on the HL-2500kfx.
- The weak dollar against the yen has hurt THP's margin in the last few years.  However the dollar has gained significant ground against the yen recently.  This means that there's a potential for a price discount for the outgoing HL-2.5kfx.  Contact Tom Rum or HRO for more details.  Dayton might be a good place to purchase either amps.
- Lastly, I typically don't buy used ham equipment.  I took exception to that rule and purchased my HL-2.5kfx used.  I knew the history of the amp. so that helped my buying decision tremendously.  The upside is that I saved $2000.  The dowside is that I don't have a factory warranty.  The amp. works like a champ (see my review of it on eham).  Used ones go for $4000 however I wouldn't buy one unless you know the amp. hasn't been abused prior.  Occasionally HRO will sell an open box HL-2.5kfx at a 10% and it comes with full factory warranty.

73,
Jonathan W6GX
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N4ATS
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Posts: 798




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« Reply #14 on: April 17, 2013, 11:56:05 AM »

There is nothing more dreamy than a set of 3CX800A's tuned up. Get an Alpha 89
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