How big does the pressurized subchassis have to be to smooth out the airflow?
My amp under construction (4cx1000a) has the socket in a 7x7x2 inch box with
the blower pushing air into the side. Too small?
Vic K2VCO
On Mar 16, 2013, at 7:16 AM, "Carl" <km1h@jeremy.mv.com> wrote:
> If youre building from scratch then Id think you would make the effort to
> accomodate the cooling system from the beginning. Use a subchassis for the
> tube that is easily pressurized (Ameritron will sell you several types and
> the blower that mates to them) or construct internal walls in a large
> chassis; companies sell those parts. Then mount the blower on the rear of the
> main chassis.
>
> If a duct is required then "Shop Vac" hoses or dryer ducts can be used. I use
> a large Shop Vac hose to cool a military surplus 432 mHz cavity amp and
> fabricated a small box to transition from the hose to the cavity air inlet.
> The hose is very flexible and allows the blower to be conveniently mounted so
> that air is drawn over the PS and control circuitry. The cavity inlet air is
> barely warm and the 2750W Pd tube is only running 1200W out (If I cranked it
> up my feedline and antenna would melt) so everything runs comfortable.
>
> Ductwork has air resistance so use as short a length as possible unless the
> blower has sufficient capacity.
>
> Carl
>
>
> ----- Original Message -----
>> I believe the air system socket connected to a duct is especially useful
>> when
>> you can't have a pressurized cabinet. There are situations where large
>> cabinets
>> are used and sealing them is not possible.
>>
>> 73
>> Bill wa4lav
>>
>> At 09:04 PM 3/15/2013 -0400, KA4INM wrote:
>>> On 03/15/13 16:58, Alan Ibbetson wrote:
>>>
>>>> For minimum airflow resistance for a forced air cooled amplifier it
>>>> would seem the blower needs to discharge in a straight line directly
>>>> into the underside of the valve socket. This leads to a fairly tall
>>>> structure with the blower underneath the RF deck.
>>>
>>>> What is the "right" way to make the physical connection between blower
>>>> and air system socket? Rigid ducting? Something resilient like rubber?
>>>> Or (what intrigues me) how about a fabric transition duct as shown in
>>>> several places here
>>>
>>>> http://users.pipeline.com.au/~burst/stc.htm
>>>
>>>> The "floppy" fabric seems attractive as a way to take up minor (major?)
>>>> misalignment between the blower and RF deck if they are built as
>>>> separate units and should help isolate any blower vibration. A competent
>>>> seamstress (seam-master) would be able to take differences in duct shape
>>>> and size in their stride too.
>>>
>>>> Has anyone got a feel for the pros and cons of the use of fabric rather
>>>> than more rigid blower couplings?
>>>
>>> I should think the difference is negligible and not worth the bother.
>>> Many successful amplifiers using all kinds of air cooled tubes have been
>>> built with the system where they are simply pressurizing the box under the
>>> tube/s with the air passing through or around the tube/s above.
>>> --
>>> Ron KA4INM - Youvan's corollary:
>>> Every action results in unwanted side effects.
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