[R-390] Black Tube Shields, IERC and cooling fans

[Don Heywood]

Another important item to keep in mind is the household AC voltage level.
I use bucking transformers on all my old equipment. I have one large one
that drops the input to my receiver(s) and S-line(s) to 113VAC. It makes
a definite difference, and the tubes love it...
Don WC4G

----- Original Message ----- 
From: "2002tii" <bmw2002tii at nerdshack.com>
To: <R-390 at mailman.qth.net>
Sent: Saturday, April 18, 2009 7:57 PM
Subject: Re: [R-390] Black Tube Shields, IERC and cooling fans


> Roy wrote:
> 
>>- The military folks had relatively unlimited supplies of spare
>>tubes.  Most of us do not.
>>- The military had a regular schedule of operational checks and
>>maintenance - radio overall performance was checked periodically, as
>>were the tubes.
>>- For most operational radios, there was a ready maintenance
>>capability - folks trained and experienced to make the things work
>>right quickly.
>>- If a radio quit, there was likely another one to use in its place
>>upon patching of the antenna and output.   Not all of us R-39x owners
>>are lucky enough to have ready spare radios handy.
>>- Some installations (as in aboard many ships) had lots of air
>>conditioning running and the spaces were quite cold.
> 
> Also, many -- perhaps most -- 390s and 390As were mounted in 
> fan-cooled racks with other receivers and equipment.
> 
> It is just good practice to keep electronics cool.  The rule of thumb 
> is that each 10 degree C rise in operating temperature cuts the 
> MTBF50 time of electronic equipment in half.  (MBTF50 is the average 
> time it takes for half of all units to fail.)  This is especially 
> true of equipment that is already well beyond its MTBF50, like most 
> tube boatanchors.
> 
> Best regards,
> 
> Don
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