[Amps] re cooling of coils

[Ian White, G3SEK]

Will Matney wrote:
>What is poor, is those junky 11 meter solid-state "contesting amps" 
>floating around with better cooling than any amateur amplifier made 
>now! The innards may be junk, but by cracky they do add the fans to 
>them. I've seen as high as four 4-3/4" high output muffin fans mounted 
>on a 1kW model.

Hams - especially the new generation of "baby broadcasters" - want amps 
that sit quietly on the table. In contrast, CB "amp contesters" actually 
*want* to hear those mighty engines roar. In both cases, the maker aims 
to please the market.

Many modern amps share the same through-flow air system as the Alpha 
amps. A particular sound-reducing feature is that the blower is buried 
deep inside the box.

This system is very good for cooling 'external anode' ceramic tubes, and 
it also promotes a general airflow around every component in the amp, 
but its weakest point is cooling the transformer. Although the 
transformer sits in the full incoming air stream, the airflow there is 
quite smooth, not turbulent, so the heat transfer is poor.

The cure for that is to add the optional Muffin-type fan on the air 
inlet. It doesn't increase the total airflow much - its main purpose is 
to make the incoming air very turbulent, so the transformer is cooled 
much more *efficiently* (along with most of the other components on the 
power-supply side). But the price for that is a noisy fan, right onto 
the rear of the amp where you can hear it.

I don't know what type of fan they supply, but low-noise Muffin-type 
fans are available that are at least 10dB quieter than the regular type.


-- 
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek