Let's see where to begin....okay two comments: First, please explain what
you mean by "commercial practice." If you mean broadcasting, no
broadcaster in his right mind today is running a tube rig unless he has to
(where you came up with that 1 kw and above factor I have no idea), but "has
to" is almost unimaginable now since you can get a 250 w. s.s. AM BC rig for
less than a lot of ham transceivers, and any of them including 50 kw boxes
practically pay for themselves in about 3 years because they are 90%
efficient, need essentially no maint., and just sit in a rack or cabinet and
tx night and day for years--no tube tx does that...and if an RF module does
fail, no big deal they are hot swappable, you loose a few hundred watts, pop
in a good module and on she goes unlike failure of a final tube where you
hope the aux fires up okay or ur off the air....go to NAB, ask any broadcast
engineer if he'd like to run a tube rig...I've never had any of them tell me
yes to that question.
secondly, all statements below were made pretty much 35 years ago when solid
state exciters started coming out and the last time I checked on the bands,
lots of hams were operating s.s. rigs into all kinds of loads albeit with
matching networks, and not many are giving up and going back to tube rigs so
they can tx into a bedspring or some bizarre load without a tuner. So, no,
I think the market for what is basically a 1.5 kw 2nd PA on your exciter is
going to soon spring open as hams retire their tube amps for one reason or
another and the costs of these amps start to drop as more mfrs. enter the
market. Now, that doesn't mean everyone is going to run out and get one,
to be sure. I for example ragchew and park on a single frequency for hours
sometimes and I don't mind manually tuning everything; in fact I enjoy it,
so I won't be in any big hurry to get rid of my Centurion. But if Mother
Nature got rid of it for me, and I had the $$$, sure, I'd go s.s. and never
look back and I doubt if I'm the only one.
73,
rob / k5uj
Unsigned message posted below:
<<<Commercial practice STILL uses tubes for 1KW and above. I have a Icom
2KL which works nicely IF the SWR is less than 2:1 - IT NEEDS its
companion AT-500 (which I also have) to keep it happy Also have a
Harris AM-7223 and a Collins 30-S1 both the Harris and the Collins will
load up into a bedspring without a external tuner the Harris will tune
automatically the collins we do the old fashioned way. I think tubes
will be around for a while yet until truly HV junctions can be devised
at a economical cost at which point the impedance mismatch issue will
become moot and hollow state devices will pass into history
Part of the issue here is that SS finals are designed to load up into a
50 ohm characteristic impedance ONLY where a tube anplifier is designed
to compensate for a complex impedance and it considers the antenna
system as part of the tank circuit since the tube can handle the high RF
voltage created by a impedance mismatch it is possible to tune the
circuit until it comes into resonance and a reasonable impedance
value. Since the transistors junctions cannot handle a high RF
voltage the protection circuits need to reduce power until the reflected
voltage is within the junctions ability to handle the voltage.
>>>
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