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Author Topic: Repeated "ON/OFF" cycles vs. "just leave it on"...  (Read 2689 times)
AE5X
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« on: October 20, 2012, 02:04:49 PM »

With the DXpedition season now upon us I find myself cycling the amp (AL-80BQ) on and off maybe 4x a day, primarily for lowband catches. A part of me wonders if it would be better for it just to leave it on if I think I'm going to be using it again in 2 or 3 hours.

I'd be interested in what you sages think...for what period of time of non-use will leave it on, after which you just turn it off?

73,

John AE5X
http://www.ae5x.com/blog

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KC4MOP
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« Reply #1 on: October 20, 2012, 02:27:45 PM »

I would just leave it on. It will save the tube from the cold start shock. 24/7 in stdby may not be good for the tube idling with no plate voltage once in a while.
Others may give better advice for a 3-500 in a stdby mode.

Fred
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W8JX
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« Reply #2 on: October 20, 2012, 02:37:03 PM »

I would turn it off. Directly heated cathodes like on 3-500z are not very fussy and heat up in but a few seconds. The cathode has a finite emissivity life and even idling counts. With indirect heated tubes like 8877 or 3cx800 you might let it idle in that they take 3 minutes to warm up.
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N4CR
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« Reply #3 on: October 20, 2012, 05:52:26 PM »

On my Collins 30L-1, there are some design issues that dictate some usage. On one hand, the tubes light up and are ready to produce full output in a couple of seconds. On the other hand, if the power switch fails it is unobtanium. This is made worse by the lack of a standby switch.

Since I need to favor fewer cycles of the power switch, I have it plugged into a power strip that can be switched on and off. And I put a switch in the keying line for an outboard standby switch.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
WB2WIK
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« Reply #4 on: October 22, 2012, 02:09:56 PM »

On my Collins 30L-1, there are some design issues that dictate some usage. On one hand, the tubes light up and are ready to produce full output in a couple of seconds. On the other hand, if the power switch fails it is unobtanium. This is made worse by the lack of a standby switch.

Since I need to favor fewer cycles of the power switch, I have it plugged into a power strip that can be switched on and off. And I put a switch in the keying line for an outboard standby switch.

It's design dependent for sure; the AL-80B has a "soft start" (inrush current limiting) circuit, standard and part of the design.  The switch isn't slammed very hard at all, nor is anything else; and the switch is readily available, still made, and stocked by Ameritron. Wink

Rather than let the amp sit idling for 2-3 hours at a time, I'd shut it off and turn it back on.
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KD8MJR
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« Reply #5 on: October 22, 2012, 02:39:01 PM »

This is one of those questions that 100 years from now people will be scratching their heads about it.  Shocked

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K0ZN
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« Reply #6 on: October 23, 2012, 03:49:10 PM »

Four times a day is probably pushing it...... but it would probably be very hard to come up with accurate, documented data one way or the other. I would look at it in the
reverse:  how often during the day will you absolutely be sure you WON'T be using it??.....if that runs over 4 hours, I'd probably turn it off.
 
"Typically" (and I use that term loosely...) a fair number of components *may* be more likely to fail when hit with repeated on-off cycling than constant service. Certainly, the one known is that the tube filament's life has a better chance of being shorter with more cycling. I highly suspect that very few ham amplifiers die from excessive hours of idling, but I would bet a large number die from cycling. What is known is that tubes in broadcast applications last for huge numbers of hours in some cases.

If you use it 4 times a day and nearly every day, that would be a LOT of on-off cycles. You do the math....... 

If you end up leaving it on and run up some hours, don't forget that it is important to clean dust from the fan and other interior parts once or twice a year.

I suspect you will get a wide variety of opinions on this question !

73  K0ZN
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WX7G
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« Reply #7 on: October 23, 2012, 06:38:28 PM »

Now it's time to consider the life of the HV aluminum electrolytic capacitors.
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W8JI
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« Reply #8 on: October 24, 2012, 05:20:49 AM »

It is a different world today with import parts, plush use and bause varies, so it is impossible to predict which way is better.

Generally, if I had instant-on type tubes, I would turn the amplifier OFF.

If I had a heater cathode tube of good quality, like an Eimac 8877, I'd most certainly not cycle filaments off and on very often.
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K4JJL
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« Reply #9 on: October 24, 2012, 01:59:26 PM »

Is the cost of the tube going to outweigh your power bill savings?  How about the life of the fan bearings and dust cleanings.
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W8JI
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« Reply #10 on: October 25, 2012, 09:50:14 AM »

It is a different world today with import parts, plush use and bause varies, so it is impossible to predict which way is better.

Generally, if I had instant-on type tubes, I would turn the amplifier OFF.

If I had a heater cathode tube of good quality, like an Eimac 8877, I'd most certainly not cycle filaments off and on very often.


I have troubles with spell check and eHam I guess. That should have been:

It is a different world today with import parts, plus use and abuse varies, so it is impossible to predict which way is better.

Generally, if I had instant-on type tubes, I would turn the amplifier OFF.

If I had a heater cathode tube of good quality, like an Eimac 8877, I'd most certainly not cycle filaments off and on very often.


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