On 4/6/2011 8:38 PM, Al Kozakiewicz wrote:
> Thanks.
>
> You've reminded me that there is a blower speed selector in the cabinet and I
> should definitely make sure that it's running at the max for RTTY contests.
If it's capable of 1500 for 30 minutes key down or 2500 for 30 seconds,
then the 10 on, 10 off, 10 on for 30 minutes is 67%. "I'd think" it
would do fine running 1500 as long as it's given enough time to cool.
OTOH I'd stick some thermocouples, or thermistors in so I could measure
the exhaust air temp as close to the tube as safety would permit. I'd
also put one on the transformer core which is probably the most
pertinent at the legal limit.
As the tube is going to reach max temp within a minute when running at
1500 out, key down and they are talking 30 minutes it almost has to be
the transformer temps doing that limiting. OTOH at 2500 out which is at
the limits of the tubes dissipation rating, that may be due to the
ability to cool the tube. Of course it could also be related to the size
wire in the transformer. I don't know how many KVA it's rated for and
at what temperature rise.
73
Roger (K8RI)
> 73
>
> Al
> AB2ZY
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Roger (sub1)
> Sent: Wednesday, April 06, 2011 6:23 PM
> To: amps@contesting.com
> Subject: Re: [Amps] Alpha vs Henry
>
> On 4/6/2011 5:05 PM, Al Kozakiewicz wrote:
>> Can anyone tell me how much power an AL-1500 is rated to produce at a 100%
>> duty cycle?
>>
>> During RTTY contests and outputting about 1000 watts, the tube side of the
>> cabinet gets mighty warm.
> It should. Running 100% duty cycle and 1500 watts out at 60% efficiency
> means you are dissipating 1000 watts. That is a LOT of heat. The temp of the
> exhaust air depends on how much air (CFM @ however many inches of
> H20) the fan can push. The 8877 is a relatively small tube for its ratings,
> but it has a fairly efficient radiator. OTOH that means a blower that can
> produce a fair amount of back pressure is required to get full output from
> the tube.
>
> As a comparison, when I had an all electric house I heated the basement and
> ham shack with 4400 watt space heaters mounted in the walls. In the dead of
> winter it only took a few minutes to heat the 13 X 21' den to about 70
> degrees. After that the heater would only kick on a few times for only a few
> minutes per hour. That means your amp running under these conditions puts out
> enough heat to require opening the den door to keep a reasonable temp. IOW
> you could heat a good sized room with that amp on RTTY.
>
>> The power supply side seems cool - but then, that's with the cover on. I
>> don't know how hot is too hot and it would be useful to know at least how
>> much continuous power the supply is rated for.
> If you were running large glass tubes that depend on radiation that cabinet
> would be too hot to touch.
>
> 73
>
> Roger (K8RI)
>
>> Tube cooling is probably another issue...
>>
>> Al
>> AB2ZY
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