[Amps] Miller-Larson effect on thoriated tungsten filaments

[Carl]

> Actually Carl, not to disagree but I saw a lot of 3-500's with "bad 
> filiments".  But in truth, they were not bad.  Instead a cold solder joint 
> had formed in the tube pins themselves.

** Mark, those were almost always due to horizontal fans and insufficient 
air on the filament pins. Very common in the Heath SB-220 family and a few 
other brands.


 Resoldering them normally fixed the
> problem, and so did keeping a close eye on the sockets.

** Once the nickel plating on the Johnson socket pins turned black they were 
beyond salvage. I dont know how many pins I bought from Johnson but I had to 
order 100 minimum.


> When I was in the Marine Corps (which is to the Navy as is the chain on an 
> old toilet... part of it, but not IN it), we used to modify the Collins S 
> Lines so as to keep the filiments on ALL the tubes turned on constantly. 
> The primary goal was to reduce drift, but the Reps from Collins also 
> claimed it would extend the life of the tubes.  Hard to make specific 
> claims as to whether it worked or not.

** When I was in the Navy is, I believe, when the 24/7/365 rule came into 
play on radio gear with miniature and octal tubes. OTOH the radar along with 
displays and fathometer were turned off in port. This would be in the early 
60's. The equipment in Emergency Radio was only turned on for exercises, PM, 
and me operating  /MM, SWLing, or piping music and other requested items 
into various crew areas from the RBB most of the time.

> Much ado about nothing to some.... interesting information to others.

** It made interesting reading but was more application specific to the 
broadcasters and others using those tubes. Also filaments improved over the 
decades and those that were fragile in the 30's had a long life in the 60's 
comparing identical designators.

RCA also made a late 30's study on useful power tube hours and concluded 
that running the filaments at a reduced filament voltage when in standby 
gave longer service, and less electric cost, than the other options but 
these were also tube type specific. Im sure there are additional studies 
from other manufacturers.

Carl
KM1H


> ----- Original Message ----- 
> From: "Carl" <km1h at jeremy.mv.com>
> To: "Mike Waters" <mikewate at gmail.com>; <amps at contesting.com>
> Sent: Tuesday, June 25, 2013 9:14 AM
> Subject: Re: [Amps] Miller-Larson effect on thoriated tungsten filaments
>
>
>>I doubt if that has much effect on our low power tubes Mike but the "boys" 
>>with the 10-20KW rigs might be interested.
>>
>> I also never had to replace any of the WW2 era TX tubes while in the USN 
>> and those were cycled on only when necessary.
>>
>> Much ado about nothing for this forum. When was the last time you saw a 
>> 3-500 with a bad filament?
>>
>>
>> ----- Original Message ----- 
>> From: "Mike Waters" <mikewate at gmail.com>
>> To: <amps at contesting.com>
>> Sent: Tuesday, June 25, 2013 12:32 AM
>> Subject: [Amps] Miller-Larson effect on thoriated tungsten filaments
>>
>>
>>>I discovered some new (to me) information on maximizing the life of
>>> amplifier tubes with thoriated-tungsten filaments. I just uploaded it 
>>> to:
>>> http://www.w0btu.com/miller-larson_effect.html
>>>
>>> Basically, every time the tube filament passes through a certain
>>> temperature range as we turn it on (or power it down?), we shorten the 
>>> life
>>> of the filament, due to the Miller-Larson effect.
>>>
>>> I would appreciate any comments on it, good or bad.
>>>
>>> 73, Mike
>>> www.w0btu.com
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>> -----
>>> No virus found in this message.
>>> Checked by AVG - www.avg.com
>>> Version: 10.0.1432 / Virus Database: 3199/5939 - Release Date: 06/25/13
>>>
>>
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1432 / Virus Database: 3199/5940 - Release Date: 06/25/13
>