On 8/16/2011 2:01 PM, John Lyles wrote:<snip>
>
> As a designer of power amplifiers using both tubes and transistors, I
> see a good trend in solid state, with 1200 watts or more per device. But
> I don't expect to see a megawatt in a device, something that I can and
> do see with new tubes. Ham radio will eventually quit using tubes except
> for nostalgia reasons;
I really don't see wide adoption of SS legal limit amps until the
devices can be made more rugged, can be cooled more easily, and become
available at much lower prices. Prices are based on tooling set up
costs, number of units produced per batch, amount of silicon in the die
compared to the base wafer size, and yield efficiency. At present they
are just too fragile and the protective circuitry (which is more
complicated than the amp) really pushes the prices far too high for wide
spread adoption.
Semiconductor devices have the potential for eventually resulting in
rather inexpensive, legal limit amps with plenty of overhead. I don't
see that happening within the next 10 years and maybe 20, but advances
in solid state tend to come in jumps rather than a slow steady pace so
it *could* happen tomorrow to quote a TV show. Unlikely but it could
happen.
Except for quite expensive and complex amps (or medium power) I really
don't see solid state amps becoming wide spread. 800 to 1000 watts
seems to be the current limit or dividing line between the high priced
spread and the rest of the pack.
> we are still seeing a few 304TL and 450TH
> amplifiers getting built due to having the parts and for fun. As long as
> their is a market, the Far East will provide bottles for building simple
> amplifiers. Don't expect any new tubes for this,
Some of those "Far East" tubes are very expensive while others are quite
reasonable.
The "Glass bottles" seem to be disproportionately expensive. I know of
one Chinese builder who imports tubes rather than using the Chinese
versions due to price. OTOH tubes like the FU728F which is
interchangeable with the 4CX1500B except for the filament voltage are
very reasonable at substantially less than the Chinese version of the
8877 and you can get 2500 watts PEP or 2 KW nominal out of one which
gives plenty of overhead for running digital at the legal limit. OTOH
unfortunately they seem to be suffering a rather high rate of infant
mortality. If they run past a month or two you probably have one that
will last for years.
Too bad the RUSSIAN tube industry is pretty well shot. They had some
very good tubes for high end amps but availability became a problem.
OTOH if you purchase a 100 FU728F's and have to test every one for 50 or
100 hours "under load" that in itself becomes a substantial portion of
what you have to charge for the tube.
My experience with the 728F's has been mixed. I've used new ones and
also NOS. I've had several fail within the first 50 hours. The ones I'm
using (rotating) through my one amp at present appear to be good ones.
However I'm planning on building up 3 amps using the 4CX3000A7 running
class A with the legal limit out. (HF, 6-meters, and 2-meters) My only
complaint about the tube is the size. It's just too big for a compact
desk top amp. With the tube being over 9" tall, I'll end up with an RF
deck about 14" tall and fan noise is likely to be a problem. I may have
to either remote a large fan or remote the amp with a control head
mounted in a compact desktop cabinet that appears like a compact amp.
Still running the legal limit out in Class A means the tube will be
close to it's dissipation limits and I won't need much additional heat
in the winter. <:-)) OTOH I have a couple of tested 4-1000As I'd like
to build into HF amps just for (as you say) nostalgia. I also have some
of the RUSSIAN GU81M which is also a large glass bottle (Pentode)
although its performance fall off rapidly with frequency compared to the
4-1000A.
By far the best bargain are the YC156 pulls IF you can stand the long
warm up time. I don't have that much patience.
> however. HV power is
> getting harder to come by due to cost of iron and copper. Switch mode
> technology comes just in time.
I still like Iron, but they can run a 1/4 of the amps cost and one that
will run the legal limit and stay cool is both large and heavy. IOW 1500
out class A can take as much as 6 KVA input @ 25% efficency. That's
about a 100# even with the new hypersil construction and I've not found
a "switcher" that I really feel is satisfactory for running the legal
limit at roughly 3 to 4 KV.
73
Roger (K8RI)
> 73
> John
> K5PRO
>
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