[Coco] Linux RBF filesystem support
gene.heskett at verizon.net
Sun Nov 2 00:35:31 EDT 2008
On Sunday 02 November 2008, jdaggett at gate.net wrote:
>Nice pics in the txpix section. The Harris transmitter looks real clean.
>Do you actually fire those two transmitters up? It sure looks like you do
> with all that wiring and hardware.
>What tubes are used in the finals?
So that's where all my bandwidth went :)
Yes, the old GE is on the air, and has been since the late 50's. The Harris
is recent and I'm in the process of restoring it for use as the amplifier for
our digital channel when we go up to full power, and digital on our original
channel, 5. Currently our digital is a 200 watt puny-power on channel 6. The
amplifiers in the Harris are identical, and the aural one could be retuned
for full bandwidth and used as a spare, or if the hassle of combiners could
be handled, even as a parallel setup.
The GE has quite a lineup of ancient tubes, one of which is the 4-1000, and
the last decent pair of them on the planet is in there now. By February and
analog shutdown time, we will be probably down to 75% power because they are
fading slowly. Those tubes haven't been made in about 15 years now. The RF
stages are, a pair of 4cx250b's as the modulated stage, they drive the pair
of 4-1000's, which in turn drive a pair of 3cx2500's to make nominally 5 kw.
That gets fed to the next cabinet, with a big old honk of a water cooled
triode (5681?) in it for the final. Rated at some large plate dissipation
I've forgotten, it supposedly can make 75kw synch tip peak on channel 6, when
tuned a full 6 mhz wide. Our setup only hits 26.7 kw synch tip peak, so one
of the first things I did when I walked in the door in 84 was to turn its 12
volt heater down to 10.5. The one in the socket now is running at 11.25
volts and is several years old. We've used 3 of them, rebuilt by econco,
since 84. One failed shorted when we slammed the cabinet door (its a bitch
to close fully), and another failed gassy. The previous engineer ran them at
full voltage which ran them out in 6 months. That was $24k a year for tubes
we destroyed by sheer stupidity. Then there were 2 of them as the aural also
used one, but after looking over the engineering I realized we were still
running on a grandfathered license that spec'd equal power for both carriers.
Since the aural only needs a few percent of the visual to work correctly, and
actually work a lot better than when both at at full power, the commission
allowed us to reduce the aural power about 30 years ago, so I bypassed the
final, which put about a kilowatt of aural on the air direct from the aurals
driver (another pair of 4-1000's) and figured I could always put it back when
the phone rang with a complaint. It hasn't in 15 years, so I even cut the
water lines to it a couple of years ago. One less set of leaks to worry
Probably more than you asked for, James. :)
And that Harris is older than it looks at first glance, it was made in '71.
It was the first IF modulated transmitter. And this one is first generation.
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