[AMPS] SB-220

[Phil Clements]

At 11:18 PM 6/18/97 +0000, you wrote:
>
>> Why screw up a near-perfect circuit? The filament transformer is specially
>> designed to be self-limiting on inrush current. The 3-500Z has instant-heat
>> filaments. You are not hurting a thing when you turn it on and off. You are
>> eliminating a major source of failure...HEAT.
>
>Hi Phil,
>
>As I understand what you are saying, you seem to be  indicating 
>turning the filament off and on does not decrease tube life.
>
>If so, I disagree with that.

Everything that happens to a tube after it leaves the factory decreases
its life....even sitting on a shelf. (especially sitting with the plate
horizontal on a shelf) My experience is that the tube will outlast the
SB-220 if it is treated per instructions in the manual. If it is not,
something other than the filaments will usually fail first. The typical
amateur should live so long to worry about an inrush protected instant
heat filament. 

snip.... 
>This damage is accumulated over a period of many temperature 
>cycles.

I would guess thousands on the SB-220.
>
>If I intended to drop the amp in and out of line during one 
>operating session, I'd simply open the relay line while leaving the 
>filament on, avoiding needless wear and tear on the filament.

You and I both do this, but why do so many Heath owners out there think
they have to go in and add internal switches, relays etc.? Just kill the
key line, and you are done!

(((73)))
Phil, K5PC

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