Kind of like babying fuses.
Do you run them at 100% or at 10% ?
Don W4DNR
Quoting Carl <km1h@jeremy.mv.com>:
>
> ----- Original Message -----
> From: "Charles Harpole" <k4vud@hotmail.com>
> To: <amps@contesting.com>
> Sent: Thursday, June 14, 2012 3:17 AM
> Subject: [Amps] "babying" radios and tubes, can do or not?
>
>
>>
>> I want to know if there are any REAL benefits from babying a radio
>> or an amp?
>
> ** Yes but you have to seperate facts from myths
>
>
>>
>>
>>
>> I hear lots of talk about running lower RF power to "save the
>> finals" or "save the tubes" and even hear people talk about turning
>> radios off for taking a one hour (or less) break.
>
>
> ** Ive managed to keep the original Eimac 3-500's in my 1964
> LK-500ZC by running at 1200W and regularly gettering them. At the
> same time the TS-940/TS-950SD are run at 80W which cools down the PS
> a bit plus has better IMD. Only one PS board failure since 1987 in
> the 940 and they are notorious for that.
> I also have a 3 holer Alpha 76PA that also runs 1200W as its not
> worth the ~1db difference based upon replacement cost of 8874's.
>
> On the shelf is a Dentron MLA-2500 and DTR-2000L both with original
> tubes, 2X 8875 and 8877 respectively. They get used once in awhile
> to keep the replacement caps reformed and the tubes gettered.
>
>
>>
>>
>> We do know, probably, that high inrush current may stress parts
>> inside tubes. But, there must be some smart folks who test things
>> to destruction who can speak with scientific instead of parental
>> certainty about this.
>
> ** For most ham style amps that is a myth as the cold resistance of
> the filament causes a properly designed transformer to be self
> limiting. This is especially important with directly heated tubes
> such as the 3-500 where way too many go into a panic and get poorly
> designed step starts. Consider that the 3-400/3-500 filament is the
> same as used in the 4-250A/400A since the 40's with no such
> silliness required.
> The only benefit of a step start is to save undersized power on
> switches and then the step start fails and takes out the resistor
> when least wanted.In the SB-220 the switch is almost unobtanium but
> there are work arounds. In an Ameritron the usual step start
> failure blows the resistor and line fuse and if the owner keeps
> trying fuses the transformer complains or the damage is already
> done. Its a very poor design.
>
> Unless overly high C caps (totally unnecessary) have been stuffed in
> a commercial amp the PS doesnt need a step start, the transfomer
> clunk at turn on is non destructive and the 1N5408 and larger diodes
> can easily take the surge. The 270uF caps available from Ameritron
> are more sufficient for the normal user; forget about the obsessive
> ones. If buying elsewhere the 330uF are OK but 470uF is pushing it.
> I use 330uF Snap-Ins in SB-220's since they fit the blocks
> perfectly, always turn on in the CW position and the switch survives
> if it hasnt already been beat to hell and back over 30-40 years.
>
>>
>> It seems to be true that one can run any of the usual amp tubes at
>> rated specs for hundreds of thousands of hours before they really
>> go bad?
>
>
> ** Pure myth. The average tube is good for 10K hours in proper use
> and running at proper full spec before emission starts to noticably
> fall off. Many do more and others less, especially the latter for
> Chinese tubes. If I average 1 hour a day over the 26 years on my
> LK-500ZC it hasnt reached 10K yet. At 2hrs/day thats a hair under 19K.
>
>
>>
>> I guess tiny impurities in the metal and not a perfect vacuum does
>> lead to failure eventually, but what are the real reasons?
>
>
> ** GAS and not to be confused with seal leage to outside air. Ive
> gone over the gettering process on here enough times and Im not
> going to keep repeating myself.
> All glass tubes outgass and destructive internal arcs do happen that
> are preventable. Most ceramic-metal tubes do it a lot less and the
> gettering process is simply normal use. Seal leakage is almost non
> existant altho certain tubes with glass seals in the base are prone,
> ask anyone with PL-172's.
>
>
>>
>> What is the real physics condition of a so called "soft" tube? Why?
>
>
> ** Loss of filament/cathode emission due to
> .. hours
> .. under/over filament voltage
> .. excessive dissipation, this can also be due to dirty cooling
> systems and nicotine covered glass tubes. Heat is a killer.
>
>
>>
>> What is really the cause of transistor failure if always operated
>> within specs?
>>
>
> ** Gremlins
> .. parasitics
> .. voltage spikes
> .. poor VSWR/intermittent relays coupled to insufficient protection circuits
> .. Other component failures
>
> The average power transistor is made up of many small transistors in
> parallel under the cover. If say 24 are on the wafer and ony 18 are
> needed to meet spec they get shipped as there is no way to know how
> many are good to start with. Each wafer is not inspected and its a
> rare case that any are ever perfect.
> As each subsequent one fails the others carry the load until there
> is total failure.
>
>
>
>>
>>
>> And, if you run your 100 watt radio at 80 watts, are you "saving"
>> the radio or just your electric bill?
>
> ** I dont pay attention to my electric bill, if I cant afford it I
> should get rid of the 5 PC's and 3 TV's first.
> To me it only means less stress and better IMD. The sweet point
> varies in a curve and 50W may be horrible but 80 is just about a
> given with a nominal 100W rig.
>
>> Inquiring minds want to know. Please.
>> 73
>> >
>> Charles Harpole
>> k4vud@hotmail.com
>>
>
>
> ** Hope Ive answered a few questions before proceeding to Part Deux
>
> Carl
> KM1H
>
>
>
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