[Premium-Rx] Harris 110A Thermal Management Issues

[S. Schappert]

I would be *very* careful with this one !

Anytime you "quiet" a fan by attenuating the airflow e.g. with a piece of foam, there may be negative consequences. This being from increased heat on the amplifier tubes over the long-term. The amplifiers cooling capacity was engineered and built to a specification constructed to maintain the tube manufacturers cooling specs plus overhead. I believe that the sum of these exercises determines and specifies a specific airflow rate (which may vary by thermal control). It is common knowledge that any increase in heat will result in shortened lifetime of the component(s). The greater the magnitude of heat, the shorter the lifetime.

Unfortunately, many amplifiers like the Harris were not designed for "shack" use. The annoyance from fan noise is the trade-off of using higher powered amplifiers. Maybe you are willing to reverse-engineer the cooling system and use quieter components (like a different fan with specific blade configuration to reduce noise with the same airflow), and maintain the factory-specified airflow rates, that may be the right thing to do. The choice is yours.

Thermal management is critical for both equipment performance and component lifetime. If you are willing to compromise either of these, then your alternatives are many. Else consider that the amplifier was built "as-is", noisy. Thermal management was the objective, not the aural comfort of the operator. There is a tendency to mount and use premium equipment based on *our* requirements as opposed to requirements that the equipment was built for. Cooling configurations that are not well "liked" and modified will ultimately destroy receivers and amplifiers. A little thermal knowledge goes a long way in maintaining equipment and maximizing lifetime.

The warning "not to fool with it" may have been someones "life-lesson" that was costly to them. I think there is hidden wisdom in that warning.

Regards to all,

-Scott 



-----Original Message-----
>From: Berndt Josef Wulf <wulf at ping.net.au>
>Sent: Feb 11, 2011 1:36 AM
>To: premium-rx at mailman.qth.net
>Subject: Re: [Premium-Rx] Harris 110A 1 kwatt rf Amplifier question
>
>On 11/02/11 Blair Batty wrote:
>> Gentlemen:
>> 
>> My Question: Does anyone have any experiance quieting down
>> the fan in the Harris 110a Power Amplifier? I seem to remember
>> someone warning not to fool with it, or I'll melt the tubes...
>> 
>
>G'day,
>
>Lookup VK2BLC on QRZ.com for practical ideas and solutions. 
>
>I only use a piece of foam that I had lying around that reduced the noise so 
>to a more comfortable level - see
>
>http://www.ping.net.au/index.php?mode=equipment
>
>
>73, Berndt
>VK5ABN
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