On Mar 28, 2005, at 5:57 PM, Steven Cook wrote:
> Mega - Ditto's...
>
> Tubes are still the way to go unless you need your amp on battery
> power.
>
> At ~ $50 each, the 4CX800 is hard to beat. For the money, they are a
> better deal than the 3-500Z, even in it's heyday. If you purchase an
> extra
> set of 800's at the get-go, you could very well be set for life.
>
> Life's too short for QRP...
In Purgatory, all signals are so hellishly weak they can't be copied
more than 50%.
>
> Steve - WG7K
>
>
> ----- Original Message -----
> From: "Will Matney" <craxd1@ezwv.com>
> To: <amps@contesting.com>
> Sent: Monday, March 28, 2005 6:03 PM
> Subject: Re: [Amps] Solid State HF High power linear amps
>
>
>> Yup,
>>
>> Plus the solid state designs splatter something awful without a
>> filter on
>> the end. Most amateur amps have a switchable filter on the output
>> (switchable between each band). Also, if you have a high SWR
>> condition, a
>> transistor is generally toast unless you have a bunch of safety
>> circuitry
>> to prevent it. A tube can handle the beating with no ill effects for a
>> period of time. Some of the large ones I've seen using up to 32
>> transistors had to use welding cable to supply the power due to the
>> very
>> high current involved. Most transistors for this frequency range (2-30
>> MHz) run on 12-18 Vdc and just a few higher. The transistors were
>> really
>> designed to be used as a single push-pull stage even though they can
>> be
>> split and combined.
>>
>> If it were me, and were going to start a new one, I'd build using a
>> couple
>> of 4CX800's.
>>
>> Best,
>>
>> Will
>>
>> *********** REPLY SEPARATOR ***********
>>
>> On 3/28/05 at 12:13 PM David Kirkby wrote:
>>
>>> Prasad Agrahar wrote:
>>>
>>>> Group
>>>>
>>>> Once a very active ham, I have been inactive for many years.
>>>>
>>> Same here
>>>
>>>> I have
>>>> started dreaming about getting back into this exciting hobby. Signs
>>>> are clear that the day is fast approaching. I was a home brewer and
>>>> I
>>>> will still be one. My wish is to gather parts to build a decent HF
>>>> high power linear soon.
>>>>
>>>> That made me wonder whether I must focus on building a tube (valve)
>>>> amp or is there any other choice? Tubes are not made any longer.
>>>> Tubes
>>>> that are available in the market are old leftovers and soon, there
>>>> will be no more.
>>>>
>>>>
>>> There are still made. There are numerous manufacturers still in
>>> business, with Eimac the best known, and probably the largest.
>>>
>>>> I noted that discussion on this group is mostly about tube (valve)
>>>> amps. But it is fact that all commercial rigs are all fully solid
>>>> state and with transistor finals. If so, why no one talks about
>>>> building high power transistor amps? Is any one working on home
>>>> brewing project? Is it the cost of transistors or is it the
>>>> technology
>>>> that makes it difficult?
>>>>
>>> One issue I see is that for very high power you are going to need
>>> either:
>>>
>>> a) Lots of transistors
>>> b) One tube
>>>
>>> The chances of you finding the matched transistors on the surplus
>>> market
>>> at sensible prices is very low. So you will probably have to buy
>>> multiple devices at full commercial prices. There are numerous tubes,
>>> like the YC156 (5kW) on the surplus market at very reasonable
>>> prices. I
>>> think the cost of transistors/kW new will be more than the cost of
>>> tubes/kW, but I have not priced them up.
>>>
>>> There are very few solid state designs for multi-kW published in
>>> amateur
>>> journals. High power is usually obtained by combining the output of
>>> various modules (more complexity). Motorola had some application
>>> notes
>>> on reasonably high power. No doubt there are application notes from
>>> the
>>> manufacturers of transistors that describe ways of getting high
>>> power. I
>>> think you will find the design will be complex.
>>>
>>> Tubes are more rugged.
>>>
>>> High voltage power supplies for a few kW are easy to build, whereas
>>> 28 V
>>> or so at 100's of Amps is no trivial task.
>>>
>>> There seems to be lots of good reasons tubes are more attractive for
>>> amateur use at high power.
>>>
>>> --
>>> Dr. David Kirkby,
>>> G8WRB
>>>
>>> Please check out http://www.g8wrb.org/
>>> of if you live in Essex http://www.southminster-branch-line.org.uk/
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>>
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>
Rich Measures, 805.386.3734, AG6K, www.somis.org
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