Fan cfm

[Wilson Lamb]

A fan that close to the tubes may cause some thermal stress problems.  I 
know this is  a factor with Eimac tubes.  The most critical area is the 
seals around the pins coming through the glass, so pushing through the 
sockets is good, but I don't know how the 200 is laid out.  I had one long 
ago, but no fan trouble.
Wilson
W4BOH
----- Original Message ----- 
From: "Jan Ditzian" <ditzian at ALLTEL.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Friday, January 12, 2007 12:47 PM
Subject: Fan cfm


> OK, while I am plotting modifications to the SB-201, I am also thinking 
> about the fan.  I have already disconnected the noise generator that is 
> built into the bottom of the chassis, and I am using an external muffin 
> fan (junk box, 117VAC, circa 25 years old) on top of the rig to cool the 
> tubes.  The amp is nearly dead silent.  However, in the spirit of not 
> laving things well enough alone, I am considering installing a fan into 
> the case.
>
> I measured, and there is barely 25 mm clearance above the Chinese 572B and 
> the top cover.  This means that a 25 mm depth fan might touch the glass 
> envelopes, which is probably not a good plan.  I do not know the required 
> cfm for these tubes, so perhaps someone can guide me here. There are 
> smaller fans (e.g., 40x40x20 mm) that run on 12VDC and would provide 8 
> cfm.  My original plan was to use a big 40x40x25 117 VAC fan and get 81 
> cfm.
>
> If someone has gone through this exercise and concluded that you really 
> cannot do it safely inside on top, please let me know.  I do not think 
> that the pusher approach works as well, and I would be willing to 
> compromise and put a permanent outboard 117VAC fan on top of the the top 
> cover.  I figure that it can be screwed through the holes with really 
> skinny screws.
>
> I expect to power the fan from 117 VAC in the chassis.  I am running on 
> 220 VAC (249 actually), so I could also use a 220 VAC fan and bypass all 
> internal power.
>
> The top internal plate was removed long ago and far away.
>
> 73,
> Jan, KX2A
>
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