On Sun, Apr 29, 2012 at 10:27 AM, W2XJ <w2xj@nyc.rr.com> wrote:
> I agree with Joe
>
> Look at the broadcast industry where the TX is usually 24/7 CCS
> operation. Solid state has replaced tubes on MW up to 2 megawatts in
> power. ON VHF FM transmitters go to 40 Kw with solid state
> amplification and there are high powered solid state UHF TV
> transmitters. The key to a good solid state amp is thermodynamics. If
> the solid state junctions can not be cooled fast enough, there will
> eventually be a failure. The new LDMOS fets get more heat from the
> junction to the outside of the case than do earlier style of FETs. They
> can also withstand infinite SWR and other abuse.
>
Using the bc industry as an analogy for hams is flawed. broadcasters
have a revenue stream from which they can pay $$$ for top of the line
s.s. gear. it is cost effective for them for several reasons--lower
utility bills, less maint. costs....none of this applies to a ham who
gets on the air for a few hours / week and will not recover the extra
expense of fool proof s.s. gear. bc station = for-profit business;
ham station = hobby and money black hole
>
> Tubes are going away, especially at amateur power levels. I just spoke
> with Richardson last week. Most new non Chinese tubes are NOS at the
> manufacturer but are not being produced. This means once they are gone,
> they are gone.
Gone from some outfit like Richardson perhaps, but millions were
manufactured and will be around after we're all in the ground. You
can get on eBay right now and find 3-500z made around 1970; 866As (if
you want them), every flea market has zillions of old rx tubes and tx
and power supply tubes out of production for 50 years; I've seen
3-1000z turn up a couple of times lately for $150 to $200; it may be
maudlin but as hams go SK their tube stashes show up at hamfests and
on eBay--I assure you, don't worry about not finding a tube, unless it
is something odd like 5-500A, 5-125A, or 4cx1600B. All you need to
know is the few hard to finds and steer clear. Actually the 5-500
and 5-125 are around, they just take more diligence.
73
Rob
K5UJ
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