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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