[AMPS] Rapid Warmup Indirectly Heated Cathode Tubes

[John Fielding]

In the broadcasting industry the use of low heater voltage for a
standby transmitter is common practice.  It is known as running the
filament at "black-heat".  Virtually all modern tv transmitters in the
UK use this technique.  Advantages claimed are:

1)	Rapid warm-up of the filament when the transmitter has to take over
duty.
2)	Reduced stress of the filament on warm-up, the most common failure
in large tubes.
3)	No apparent decrease in tube life.

BTW  The cooling is applied to all transmitters in a bay from a central
cooling plant with multiple heat-exchangers.  

Typically the air circulates through the tubes and a closed circuit
heat-exchanger.  The first heat-exchanger discharges its load to an
air-water interface.  The heated water is then fed to another
heat-exchanger.  Therefore the primary air (for the tubes) is kept free
of dust particles which can cause arcing in the transmitters.

The second heat-exchanger has a different air cooling system to the
outside world.  Our local tv transmitters have a 3 stage heat-exchanger
with the final water to air exchanger built onto the outside of the
transmitter house.

Hope this is of some interest to the "reflectees".

John	ZS5JF

----------
> From: km1h@juno.com
> To: amps@contesting.com
> Subject: Re: [AMPS] Rapid Warmup Indirectly Heated Cathode Tubes
> Date: 11 January 1999 07:09
> 
> 
> 
> 
> On Mon, 11 Jan 1999 07:40:29 -0800 dan hearn <dhearn@ix.netcom.com>
> writes:
> >
> >Jon: I didn't make top of the honor roll (365 cfmd ) and 199 zones 
> >while
> >sitting on my thumbs as my amp warmed up. Obviously I call barefoot 
> >while the
> >amp warms up and sometimes make the contact that way.  73, Dan
> >
> 
> Great retort Dan!  
> 
> I believe it was mentioned on the reflector that leaving the
filaments on
> indirectly heated tubes continuously would have very little effect on
> life. Perhaps someone could elaborate....John Brosnahan or Dick
Ehrhorn
> maybe?
> 
> When I still ran the NCL-2000 I would turn it on when I came home
from
> work and leave it on until I went to bed; actual time at the radio
was
> minimal. Did the same with a 
> LK-780 ( two 3CX800's) and never experienced loss of output during
the 8
> years I owned it.
> 
> 73  Carl   KM1H
> 
> 
> 
> 
> >Jon Ogden wrote:
> >
> >> >I do
> >> >not like to think of how many times I have waited on my 8877 to 
> >warm up
> >> >while a rare DX station was calling CQ or getting ready to QRT.  
> >73,
> >> >Dan  N5AR
> >>
> >> No one says you have to wait for your amp to warm up in order to 
> >work the
> >> DX station.  Put your amp on standby while it's heating up and
call 
> >the
> >> guy barefoot.  You just might be surprised - you might work him.  
> >Lots of
> >> us work DX on 100 or 200 Watts.
> >>
> >> 73,
> >>
> >> Jon
> >> KE9NA
> >>
> >> -------------------------------------
> >> Jon Ogden
> >> KE9NA
> >>
> >> http://www.qsl.net/ke9na    <--- CHECK IT OUT!  It's been 
> >updated!!!!!
> >>
> >> "A life lived in fear is a life half lived."
> >>
> >> --
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> >
> >
> >
> >
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