Cooling the 813s

[W7SOE]

My 2x813 amp project will need some cooling.  I could mount a fan on top of the deck but that would take up room.  The 813s are mounted below the deck with a 4" cavity below.  How about sealing the bottom section with a muffin fan "pressurizing" it?  The holes for the 813's are just big enough now for the tubes, perhaps enlarging the holes or "scalloping" them to allow air to flow up the sides of the tubes?

Thanks

Rich

[ka1tdq]

I used a super quiet bathroom fan and used the 4" duct from it to pump air directly to the bottom of the tube sockets in my old dual 3-500 amp. It's just another option to consider. It had lots of air flow for AM service. Check out my QRZ page about half way down to see what I'm talking about.

Jon
KA1TDQ

[W7SOE]

Jon,
   This will be a compact desktop amp so I will need something on that scale. 

Thanks

Rich

[WBear2GCR]

They generally don't need much cooling, that's the good part.

I'd put in some small DC centrifugal blower, or blowers in the bottom of the chassis.
Or on the back - they are flat and small...
They work better into a back pressure than do regular blade fans.
There are some cheap, small surplus blowers of this type.

For extra air flow, a series of holes around the circumference of the socket hole will add to the flow.
Lantern chimneys from Coleman and similar lanterns withstand high heat and will increase the cooling,
assuming an air flow. Otoh I have been told that one can temper regular glass in an oven... so you can cut
an appropriate glass bottle and make chimneys.

                          _-_-bear

[N2DTS]

Plate modulation or linear service?
A pair in class C plate modulated service loaf along at 600 watts carrier out, 2000 volts and 400 ma.
I have two sockets mounted on a plate with loads of small holes, almost like a screen, with air blowing up over the tubes.
When I built a quad of 813's as a linear for a flex 5000 I recessed the sockets and made the holes bigger and had air blow up past the tubes.
In linear AM service they make a huge amount of heat, all tubes do in that service.

[KL7OF]

2 X 813 modulating 2 X 4-400 ...... pressure chassis  Modified RCA BTA1 S

[W7SOE]

Thank you all for the advice.  I will probably go with forcing air up from the base of the tubes.  This is to be a linear amp for ssb only so it sounds like I won't need an inordinate amount of airflow.

As always, thanks for the help

Rich

[N2DTS]

For ssb service, convection cooling will do. Makes for a quiet amp.

[Opcom]

I agree with the idea of keeping base pins cool but if it is the same amp, the sockets seem to obscure them. I recall some suggestion that if air is needed some should be directed at the glass envelope. If you don't show color on the plates then probably don't need much direct air at all, just move the hot air from the cabinet. No matter what any movement is good.

I have been using the 12V / 32CFM flat style ones here. They are fairly quiet and blast a good amount of air.
http://www.surpluscenter.com/Electrical/Blowers-Fans/DC-Centrifugal-Blowers/
I also had good luck with that vendor on other stuff.