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Author Topic: Tube Warm up Time  (Read 14420 times)
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Posts: 13290

« Reply #25 on: February 02, 2011, 12:17:54 PM »

I just read a few days ago that tubes that are designed to operate at high temperature, are best maintained at those temperatures for
so the tube will remain within manufacturing specification. That is to say that the mechanical alignment of the elements are within specification when at operating temperature.

Who else knew that??  Perhaps I can find the article??

The secrecy of my job prevents me from knowing what I am doing.
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Posts: 3483

« Reply #26 on: February 02, 2011, 12:30:04 PM »

FWIW which is probably close to nothing.

UHF TV MSDC IOTs and even regular IOTs are indirectly heated.

One example of heater burn is:

Cabinet can make 25 KW 8VSB out the pipe. Fil is 5.6 volts @ 22 amps. This thing isn't much more than a big linear amp.

Recently software was added to allow the fils to stay on. They used to extinguish after 5 minutes with no high voltage. We run the fil standby voltage slightly reduced from operating voltage.

Older UHF TV txs used a thyratron crowbar which must be fully warmed up to protect the tube when it acrs. Repeat - when it arcs. Newer sets use much less filter capacitance to limit energy with a fault. Primary power is dumped at any sign of overcurrent. All HV goes through fiber optic isolated toroid current sensors. to facilitate close monitoring.

The latest Care And Feeding has a chapter on MSDC IOTs.

Last one I replaced was $55,000.00. We got a deal.

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