>> To: David VK3EW <vk3ew@rint.com.au>
>> From: philk5pc@connect.net (Phil Clements)
>> Cc: amps@contesting.com
>> Subject: Re: [AMPS] SB-220
To: <amps@contesting.com>
>> Date: Wed, 18 Jun 97 16:52:09 +0000
>> 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.
Eimac says that tube life will not be compromised as long as the filament
inrush overcurrent remains equal to or less than the normal current. In
a SB-220, this is assuredly the case.
>
>A very common reason filaments fail is because of accumulated damage
>from constant exposure to mechanical stress from large temperature
>changes. This damage is accumulated over a period of many temperature
>cycles.
>
RE: 'Very common': We have tested many failed 3-500Zs. We have not
yet seen a 3-500Z filament fail from opening. I find it a bit curious
that Mr. Rauch does not specify the nature of the failure.
Rich---
R. L. Measures, 805-386-3734, AG6K
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