[Amps] Step-start and 3-500Z filament life

[Carl]

You might ask Merit Arnold, W6NQ, of RF Parts that question as he is a 
regular reader of this forum.

The SB-220 filament transformer is self limiting by design and allows a 
rather gentle start up. Ive yet to hear of  a filament failure using a Heath 
transformer.

I do make it a point to ensure that the actual socket voltage is 5.0V or a 
bit less. The LK-500ZC I bought new in 86  still shows full output on 10M 
and the filaments are at 4.85V, well within the 5% tolerance spec.

Carl
KM1H


----- Original Message ----- 
From: "Bill W5WVO" <w5wvo at cybermesa.net>
To: <amps at contesting.com>
Sent: Saturday, December 05, 2009 10:41 PM
Subject: [Amps] Step-start and 3-500Z filament life


>I understand why turning a tube's filaments off and on repeatedly
> shortens the tube's useful life. However, I'm not clear about the
> effects of doing this when a step-start circuit is included (as in
> the Harbaugh step-start kit, which I have installed in my
> 6m-converted SB-220). How much difference does this really make in
> the life of the tubes? I would like to stop worrying about the
> tubes degrading due to filament deterioration. The tubes are brand
> new RF Parts 3-500ZGs, and I would like them to last another 20
> years or so while enduring being turned off and on once or twice a
> day. Will the step-start process ensure that kind of longevity?
> Leaving the amp running 24x7 isn't an option due to fan noise and
> power consumption.
>
> Bill W5WVO
>
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