[Amps] Coupling a blower to an air system socket

[Carl]

It all depends upon the blower cfm/backpressure rating and the socket plus 
tube contribution. If you look at the Ameritron bases they are not very 
large or look at the various Alpha 8874 amps which are mighty small. A 
blower that is too big is not the answer either.

Carl
KM1H



----- Original Message ----- 
From: "Vic Rosenthal" <k2vco.vic at gmail.com>
To: "Carl" <km1h at jeremy.mv.com>
Cc: "amps" <amps at contesting.com>; "Bill Fuqua" <wlfuqu00 at uky.edu>
Sent: Saturday, March 16, 2013 2:30 PM
Subject: Re: [Amps] Coupling a blower to an air system socket


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 at 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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