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/
>
>
>
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