[Amps] Coupling a blower to an air system socket

[Roger (K8RI)]

On 3/18/2013 10:12 AM, Jim Thomson wrote:
> Date: Sun, 17 Mar 2013 15:37:50 -0400
> From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
> Cc: amps at contesting.com
> Subject: Re: [Amps] Coupling a blower to an air system socket
>
>>> One thing to remember about external anode tubes. They often have
>> cooling requirements listed as so many cfm at a given back pressure,
>>>
>>> I do not know of any way to achieve the required air flow at a reduced
>> back  pressure other than an exhaust fan reducing the exhaust pressure thus
>> making it a little easier to get more cooling air through.
>>> I believe Emtron and OM both use this approach on some models.
>
> ###  Roger, you have missed the basic concept of the k2riw design.

No, I have missed nothing. We are talking about two different concepts.

I am only talking about the physics involved and how much air needs to 
go through the anode structure, not the whole assembly and particularly 
not the socket restrictions.  That is why you often find even with the 
so called conventional approach that additional openings are made to 
bypass the socket restrictions.  Even the Chinese FU728F socket bypasses 
a fair amount that goes into a tapered chimney to get back down to the 
anode diameter. So these restrictions were recognized, if not cured.

What k2irw did was a study and published the results making the approach 
widely known and popular.
k2riw did not come up with the concept as it had been in use for some 
time but he is given credit and justly so because of his work showing 
how well the approach works caused it to become widely used.

When it comes to tubes like the 4CX3000 run at their ratings, whether 
you pressurize the anode compartment and let some bleed air cool the 
base and seals while ducting the anode flow out, or use the so called 
conventional approach it is going to make a lot of noise.  Done properly 
it is not a 50:50 proposition, but more like 90:10. The base and seals 
take a fraction of what the anode needs.  You don't need all that air 
flow to cool the base and seals which just get in the way  with the 
unmodified conventional approach.

Actually the 4CX3000 isn't big enough to run class A at the legal limit
25% efficiency at 1500 out makes a lot of heat.  About twice what the 
4CX3000 is rated for.

Legal limit at class A takes a big tube, lots of power and lots of air 
making lots of noise.  to get the legal limit out at 25% is 1500/0.25 = 
6000 watts input. 6000 - 1500 = 4500 watts of heat at the anode to get 
rid of.  I used to heat my basement with a 4500 watt heater.

Eimac did make some concessions with the 4CX3000 socket as it has a 
rather large ring of slots that let most of the air bypass the base of 
the tube and go directly to the anode structure.  Looking at the socket 
I'd say it runs about 4:1 as far as air flow.  I'm talking about the 
entire, very expensive socket, not the ones normally seen on e-bay 
referred to as the bikini version.

Yes, I agree that the k2riw approach works well, but that was not the 
point of my post.

73

Roger (K8RI)