Your right, I did as one is just down the road from the other. However the 500
kW was WLW owned by Crosley Radio. How would ya like to be able to afford that
station and run it legal?
Best,
Wil
*********** REPLY SEPARATOR ***********
On 4/1/05 at 6:52 PM Radioal wrote:
>I think you are mixing memories of both VOA and WLW, which were both
>located
>north of Cincinnatti.
>
>----- Original Message -----
>From: "Will Matney" <craxd1@ezwv.com>
>To: <amps@contesting.com>
>Sent: Friday, April 01, 2005 6:25 PM
>Subject: Re: [Amps] Standby tubes (was: Even more power solid-state amp's)
>
>
>> Dave your correct, the do still change them out on a time line. That's
>> where a lot of the pulls on eBay come from. However, I have seen some
>> large stations with a standby final stage, two cabinets side by side
>which
>> are switched over in case of failure. I doubt they fire up the tubes
>> heater unless it's needed. Matter of fact, the biggie here in Ohio which
>> was Voice Of America had a standby PA. It wasnt near the power of the
>big
>> monstter though. Of course they dont run that big amp any more and is
>now
>> a tourist attraction. Actually, they had to shut it down over shutting
>> Canada down. At its hay day, the Royal Family of England used to make
>> music requests if I recall. This one is just outside of Cincinnatti. It
>> was something like 500,000 watts if I recall or maybe a little more. The
>> Blaw Knox tower still stands, and the cooling ponds are still outside,
>> just grew up with cat tails. I think a group did overhaul it and fire it
>> up for the 2000 shebang. They didn't run it very long
>> though.
>>
>> Best,
>>
>> Will
>>
>>
>> *********** REPLY SEPARATOR ***********
>>
>> On 4/1/05 at 1:02 PM Dave Haupt wrote:
>>
>>>> From: "Joe Subich, K4IK" <k4ik@subich.com>
>>>> Subject: Re: [Amps] Even more power solid-state
>>>> amp's
>>>> To: <craxd1@ezwv.com>, <amps@contesting.com>
>>>> Message-ID: <000d01c536ca$a1aab4a0$c080a8c0@laptop>
>>>> Content-Type: text/plain; charset="us-ascii"
>>>>
>>>>
>>>> Will writes:
>>>>
>>>> > What if you had two final tubes, one idle until
>>>> the other
>>>> > gave up the ghost. It's easy to change over the
>>>> same way with
>>>> > way less circuitry.
>>>>
>>>> The cost of a "hot standby" transmitter using vacuum
>>>> tubes is
>>>> far higher than just the tube alone. It really is a
>>>> completely
>>>> separate transmitter with the exception of, perhaps,
>>>> the low-
>>>> level stages. In television, since pre-correction
>>>> adjustments
>>>> (linearity) generally need to be set up based on
>>>> amplifier
>>>> tuning, it is far better to 'marry' a low level
>>>> stage and
>>>> final amplifier.
>>>>
>>>> When one considers the relatively small premium for
>>>> solid-state
>>>> TV transmitters at low/high VHF and in some cases
>>>> lower UHF,
>>>> tubes did not make a lot of sense in the last
>>>> equipment replacement
>>>> cycle.
>>>>
>>>> Now, with HDTV's (digital TV) 12 to 16 dB peak to
>>>> average ratio
>>>> and the need to make up to 60 KW average output in
>>>> some cases,
>>>> specialized tubes have reasserted themselves at UHF
>>>> (though I doubt
>>>> any ham rig will ever use a multi-depressed
>>>> collector Inductive
>>>> Output Tube - MDCIOT).
>>>>
>>>> 73,
>>>>
>>>> ... Joe, K4IK
>>>
>>>As Joe says, a standby tube is a monumental task.
>>>Broadcast-sized rigs have fractional to multiple
>>>horsepower blowers, and it's a daunting task to
>>>auto-switch anodes, cathodes, etc. So you'd end up
>>>having a completely redundant PA stage with its own
>>>cooling. If the tube involved is an indirectly heated
>>>type, you'd also keep the heater running, which means
>>>a separate heater supply. And that's a dubious
>>>notion, as the wearout of an indirectly-heated tube is
>>>dependent on heater time, not cathode emission time.
>>>
>>>Further, who says it's going to be the PA that fails?
>>>Drivers fail, also, so you may as well have a
>>>redundant one of those. In the solid state designs,
>>>you often have one solid state module driving eight
>>>more, then another 64, all identical. Therefore, one
>>>module suffices as a quickly replaceable unit for any
>>>of PA, driver, pre-driver.
>>>
>>>In my days in broadcasting, stations would simply
>>>acquire the replacement tubes when the present PA and
>>>driver tubes reached a certain number of hours. Then
>>>they'd watch the PA currents and so forth, looking for
>>>signs of degradation, so that they could schedule the
>>>tube replacement at a time when the cost per minute
>>>off-air was less (2am). The major market stations I
>>>was familiar with (all in Denver, CO), had entire
>>>backup sites - a 50kW station might have a 5kW station
>>>on an adjacent mountain top, on hot standby. It would
>>>go on the air when anything failed at the main site.
>>>Stations just as often lose the audio feed as a PA.
>>>Typically, the smaller TX was the station's earlier
>>>rig, prior to their approval for higher power. But
>>>that was 20 years ago.
>>>
>>>Nowadays, most projects I work on are intended for
>>>production volumes of millions per month. You'd think
>>>a standby Pentium would be a good idea, but I suppose
>>>they don't fail very often!
>>>
>>>73,
>>>
>>>Dave W8NF
>>>
>>>
>>>
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>>
>>
>>
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