[Amps] AL1500 cooling mod?

[jeremy-ca]

>
>> Why would the electrolytics in the AL-1500 require any special airflow 
>> since
>> they are 105* C computer grade and meant to operate in a warm enviroment? 
>> You once claimed that those caps were a special order of the highest 
>> quality.
>
> The fact they say "105C* has NOTHING to do with being safe to run at 105 
> or even being "meant" to work at 105.  105C is the absolute maximum 
> temperature to fall within factory MTBF specs.


I never said that they should be run at that temperature. The fact that 
Ameritron was smart enough to buy that extra overhead compared to cheaper 
85* C caps is a big plus.


>
> Anyone working with electrolytics should be aware that the single most 
> damaging thing to electrolytic life is ambient temperature. This is true 
> for all electrolytics of that general material. There is a large decrease 
> in life as temperature is increased. While voltage is a linear life 
> shortening progression, temperature is a cube law effect.



Thats been well publicized for decades and holds true for old technology in 
particular.
QUALITY caps specifically designed for switching supplies and other high 
ripple use are amazingly long lived under adverse conditions.

Have you ever measured the temperature at the caps in the AL-1500?
In all the AL series of amps Ive worked on Ive never noticed excessive heat 
in the PS area.


> The air system in the AL-12 series amplifiers (82,1200,1500) have 40-50 
> watts total of bleeder heat above the electrolytics plus 35 watts of 
> filament transformer heat dissipation, and it is important to not let that 
> heat collect in that area.


All of the heat goes up. A bit of ventilation in that section of the cover 
might help it from becoming trapped.

I like the idea of taking the tube heat straight up thru the rubber chimney 
and out thru a low restriction mesh. It would reduce the RF component heat 
somewhat. My 3CX1000A7 144 and 222 MHz amps are built that way and there is 
no tuning drift which was quite noticable before adding the exhaust 
chimneys.

Dennys LK-800A RF components run a comfortable warm with the 3 chimneys in 
use. A big change from the DTR-2000L layout with the 8877 blowing right at 
everything horizontally.


Carl
KM1H




> 73 Tom
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