On Sun, 2006-10-08 at 17:00 -0400, jamesmozzillo@aol.com wrote:
> Probably the best method is not the instant on but keeping the filament on
> at a warm setting and turning off the high voltage supply. This uses minimal
> electrical energy while keeping the cathode warm and ready to go when the
> amplifier is turned full on!
>
> Regards,
>
> Jim NC9J
>
> -----Original Message-----
> From: john@gotwals.com
> To: tentec@contesting.com
> Sent: Sun, 8 Oct 2006 4:40 PM
> Subject: Re: [TenTec] Centurion Amp Woes
>
> I was intrigued by Rog's longevity recommendation for "Instant On" tubes,
> since I use a Drake L-4B amplifier. For ordinary tungsten light bulbs the
> bulb's life can be shortened by frequent turn-on/off due to the thermal
> expansion/contraction of the tungsten filament. In addition to the two
> 3-500ZGs, my L-4B power supply has two series connected 50 watt bleeder
> resistors which get exceedingly hot while the power is turned on, and I
> would guess that thermal fatigue of these resistors might also be increased
> by frequent turn-on/off.
>
> I would be interested in other comments on the turn-on/off vs. leave it on
> conundrum.
>
> John, N9JG
>
> -----Original Message-----
> Message: 10
> Date: Sun, 8 Oct 2006 15:26:45 -0400
> From: "RB" <K9RB@bellsouth.net>
> Subject: Re: [TenTec] Centurion Amp Woes
> To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
> Message-ID: <070501c6eb0f$b1224dd0$0201a8c0@k9rb8c670f7e81>
> Content-Type: text/plain; charset="us-ascii"
>
> [snip]
> I also might suggest that with an amplifier using 3-500Z type "Instant On"
> tubes, you will increase longevity of the tubes, as well as save on your
> electric bill by turning the amplifier off whenever you do not anticipate it
> use during the upcoming 10-15 minutes. Since the tubes require virtually no
> warm up time, turning them off when not in use is a preferred mode of
> operation. Just the 5 volts at 15 Amps of current to each tube calculates to
> be 150 watts of wasted energy. Add the fan and HV transformer and you're
> likely looking as 250 watts just in the standby mode that you have been
> paying for, expended mostly in generating heat and contributing to shortened
> component life.
> [snip]
> 73, & Good Luck!, Rog-K9RB
>
Sometimes tube filaments are supplied with current limited transformers
to reduce the inrush. Lamp inrush current can be 16 times operating
current, that's why a thin filament seems to nearly always break during
that inrush period. Limiting inrush current to 2 or 3 times running
current should improve tube longevity in the on/off situation. Lamp life
too.
I'm not sure it can be applied to a tungsten tube filament, but rule of
thumb in a quartz lamp handbook is that lowering the supply voltage by
5% lowers the lamp light output by 10% and doubles the life. Conversely,
increasing lamp voltage by 5% raises the visible light 10% and cuts the
life in half.
Tubes at WWV are run with all votages cut way back and achieve tens of
thousands of hours of continuous operation.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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