----- Original Message -----
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
To: <amps@contesting.com>
Sent: Monday, September 07, 2009 12:06 PM
Subject: Re: [Amps] 3CX800 and blower
> ORIGINAL MESSAGE:
>
> On Mon, 7 Sep 2009 10:26:42 -0400, "David J Windisch"
> <davidjw@cinci.rr.com>
> wrote:
>
>>Does a 3CX800A7 require airflow any time the filament is lit, like, say,
>>3-500Z glass tubes with tender seals and 70-watt filaments?
>>
>>I'm thinking of leaving the (unobtanium) blower turned off, to lower wear
>>and tear, until I need the power.
>>
>>Yep, I'm aware of the potential hazard of a senior moment: I have in mind
>>a no-blower-no-operate interlock scheme.
>
> REPLY:
>
> Personally, I would not risk it with such an expensive tube. The answer to
> your
> question, and the only way to be sure is to measure the temperature of the
> metal-to-creamic seals and make sure they do not exceed 250 degrees C.
>
> As the data sheet says: "It should also be noted that it is not good
> practice
> to operate at, or close to, the absolute maximum temperature rating for
> the
> metal/ceramic seals. Where long life and consistent performance are
> factors
> cooling in excess of normal requirements is normally beneficial."
>
> Words for the wise.
>
> 73, Bill W6WRT
>
The Eimac data sheet also plainly states: "Cooling must be applied before or
simultaneously with electrode voltages, including the heater,
......................"
It also goes on to suggest the use of temperature sensitive paint or other
temperature sensitive devices as part of the design phase.
Carl
KM1H
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