[Amps] Warm up and on time question...

[Carl]

----- Original Message ----- 
From: "BJ VOUTE" <fxb1982 at hotmail.com>
To: <dave at nk7z.net>; <amps at contesting.com>
Sent: Wednesday, December 14, 2011 12:38 AM
Subject: Re: [Amps] Warm up and on time question...


>
> This is what I gather:
>
> The AL-82 manual specifies warm up time as "approximately 30 seconds" 
> while the AL-80B manual states "10 seconds".  I am guessing that the 
> chimney type cooling VS the muffin fan cooling method accounts for the 
> different warm up times?


Nope, different manual writers; 30 seconds is better.


>
> W8JI states that to obtain maximum life from an 8877 tube, not to cycle 
> the heater (filament) excessively.  http://www.w8ji.com/8877_failures.htm 
> It stands to reason that this would apply to a 3-500 tube as well.


Thats nothing new and just common sense copied from as far back as the first 
AC operated table radio.The military found that out also as the MTBF went 
way up when electronic equipment was left on 24/7.


>
> The QRO HF-2000 manual states:  "After prolonged operation, let the 
> Amplifier run for several minutes without drive applied so the fan will 
> cool the tubes before you turn the Amplifier off."
>
> When I plan on operating an amplifier for 5 hours I leave it on for 5 
> hours.  I don't think turning an amplifier off and then back on after 30 
> minutes constitutes excessive cycling(subjective?), but I consider a tube 
> filament to be like a light bulb and it is said that the life of a light 
> bulb is shortened by cycling.
>
> I as well warm up my tube amplifiers for about 5 minutes and let them cool 
> down to what physically feels like idling temperature to me before 
> shutting down.  Whether this is necessary or to what extent the tube needs 
> to cool down may likely be a topic of debate but common sense tells me it 
> does not hurt anything.

Anything over 30 seconds is wasting time on direct heated tubes such as the 
3-500, 572B. 811, etc.

For indirect heated tubes (3CX800, 8874, 8877, etc)follow the tube 
manufacturers specs as amp timer circuits tend to vary in accuracy and with 
age. Anything more than spec is another time waster.

Carl
KM1H



>
> I'm looking forward to more info about this topic.
>
> 73, BJ
> k0cwo
>
>
>
>
>
>> From: dave at nk7z.net
>> To: amps at contesting.com
>> Date: Tue, 13 Dec 2011 07:30:30 -0800
>> Subject: [Amps] Warm up and on time question...
>>
>> Hello,
>>
>> I have an AL-82, my habit is to turn it on, allow it to warm for about 5
>> minutes prior to use, use the amp, then turn it back off. Sometimes I
>> find that I will be using the amp again within 10 or 15 minutes, maybe
>> 30 minutes. Is it better to leave it on for the half hour, or turn it
>> off then re power it 30 minutes later.
>>
>> Does this cause any issues over the long term? Should I just leave it
>> on for the half hour? Worried about repeated heating and cooling of the
>> tubes.
>>
>> Dave
>> NK7Z
>>
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