[Amps] Layout of tube

[Roger]

It depends some what on the fan construction, but generally the stacked 
fans should be capable of a higher pressure at roughly the same air 
flow.  When the flow is restricted as it would be with the tiny 4CX-250s 
the amount of air would be notably increased.  Unfortunately there is no 
way to know how much change you will get when stacking fans like that.  
It's more a "do it" and then "measure the change".  The specs are around 
some where that will give the flow through a given tube for a given back 
pressure assuming there are no leaks in the compartment. It's easy to 
build a U-tube manometer to measure the back pressure in inches of water 
just using some clear plastic tubing of a 1/4 to 3/8" diameter. The 
construction was in the older Handbooks and may still be in them or the 
book on classic amp design.


73

Roger (K8RI)


donroden at hiwaay.net wrote:
> I used stacked muffin fans on a 4 x 4CX250 amp, and one fan wouldn't  
> get the job done. Two worked great, and three didn't seem to be  
> proportionally better.
> Don WA4NPL
>
>
>
>
> Quoting vk3pa at vk3pa.com:
>
>   
>> Quoting James Colville <jimw7ry at gmail.com>:
>> EMTRON uses 2 fans one under the tube blowing es the other a pc type
>> fan on top
>> sucking..
>>
>>
>>     
>>> Fans in series? How are you going to figure the airflow out? Just use a
>>> single BLOWER like 100% of the other amp builders use? What tube or tubes?
>>>
>>> 73
>>> Jim W7RY
>>>
>>>
>>>
>>> On Mon, Jan 25, 2010 at 12:28 PM, MIKE DURKIN <patriot121 at msn.com> wrote:
>>>
>>>       
>>>> Ok, yea its not for VHF, Just HF but was thinking about parasitics and all
>>>> ....
>>>>
>>>>
>>>>
>>>> Next thought is there a rule of thumb when stacking fans back-to-back to
>>>> figure CFM and pressure ....
>>>>
>>>> Like if i had 2 fans with 98.1CFM/0.28" blowing in series?
>>>>
>>>>
>>>>
>>>> Mike
>>>>
>>>> KC7NOA
>>>>
>>>>
>>>>
>>>>
>>>> snip>
>>>>         
>>>>> Hi Mike,
>>>>>
>>>>>           
>>>>>> I'm wanting to supply the tube on one side of the tube and put the
>>>>>>             
>>>> blocking cap for the C.L.C. output
>>>>         
>>>>> about 110Deg off around the tube. Will that make for any internal issues
>>>>>           
>>>> ETC. from
>>>>         
>>>>> misbalance on the Anode ??
>>>>>
>>>>> If I understand you correctly, looking down at the tube, the HV supply
>>>>>           
>>>> (connection to
>>>>         
>>>>> the anode RF choke) is at 12 o'clock, and the blocking capacitor to the
>>>>>           
>>>> output tank
>>>>         
>>>>> comes off at about 4 o'clock (or 8 o'clock). If that's what you mean,
>>>>>           
>>>> that should be
>>>>         
>>>>> fine. (Unless you're working at VHF or UHF frequencies... then I don't
>>>>>           
>>>> have a clue as
>>>>         
>>>>> to whether it's OK.)
>>>>>
>>>>> 73,
>>>>>
>>>>>
>>>>>
>>>>> George T Daughters, K6GT
>>>>> CU in the California QSO Party (CQP)
>>>>> October 2-3, 2010
>>>>>
>>>>>
>>>>>           
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