Ambient temperature target

[mashaffer]

In my mini console project the amplifier will be, of course, in an enclosed though vented area. In deciding whether forced air is required I intend to measure ambient temperature in the top of the enclosed area. Of course for this to be meaningful I have to have an idea of what is an acceptable level for long term reliability of the amplifier.

Any rules of thumb to offer?

[kevinkr]

I'd try to keep ambient below 50 degrees celsius if possible, just make sure that no parts are running near their rated operating temperature or service life will be comparatively short.

Spot measurements of hotter running components can be useful.

Use 105 C rated electrolytics if you can, they will have much longer lives particularly in hot environments. Note that electrolytics experience a reduction of half their operating life for every 10 C increase in their operating temperature.

I generally tend not to worry too much, but my gear is not enclosed and is generally well ventilated.

[mashaffer]

Thanks, 50C=122F. Will check and see if there is a rating on my caps. Amp is already built so would be a bit of work to change out caps.

[Wavebourn]

Forced air does not help against radiated heat, mirrors do. For example, mirror between tubes and transformers that are on top of the chassis. Also, my rule of thumb is, to put tubes above chassis, the rest underneath, with electrolytics closer to the air intake. Holes around tubes suck an air from below, without any fans. I.e. hot tubes create conventional air flow that may be regarded as forced cooling, when properly used.

[mashaffer]

Interesting that you should mention mirrors. My wife is bugging me to build it with a transparent front so that you can see the guts. If I put a mirror between the tubes and the PT/can cap I could instantly double my tube compliment. I am resisting her request at the moment since I feel that my layout is a bit too industrial to be considered a true work of art like your amps are (I mean that sincerely).

I have some holes around the perimeter of the tube sockets primarily as alternate mounting orientations since I wasn't sure of the best socket alignment when I drilled the chassis. The holes would provide some ventilation but not very much I think since they are small.





There is about an inch open on each end of the chassis so even sitting flat on a surface there is the ability for air to enter from below but I plan to mount it over an open hole (with screen for safety) to allow outside air in. Two long slots in the top of the cabinet will form a carrying handle which will allow air to escape the top and I plan the normal perforated back panel also.

Here you can see the underside and the clearance on each end.



And the power amp under test.



There will also be a preamp mounted inside but there won't be a lot of heat from that.

Really appreciate the input guys.

[trobbins]

Glass is opaque for the radiated heat temperatures you may want to barrier. It only just starts to become partially transparent at hotter temperatures such as output valve plates at full bore.

Ciao, Tim

[Wavebourn]

Hi Tim;

what about transparency of Lexan for IR radiation? It would be easier to use Lexan mirrors instead of polished metals. Also, Snowroof paint looks promising.

Edit: here is the link http://www.snowroof.com/product_deta...oduct_id=SR104

[trobbins]

If you google on lexan and infra-red and transmission you will see that lexan type products are pretty much opaque at low temperature infra-red radiation (ie. similar to glass).

High reflectance coating appear to work well at visible wavelengths (eg. http://www.solacoat.com.au/rs/7/site...Competitor.pdf) - and I would suggest that they may act with good emittance and reflective characteristics at longer infra-red wavelengths.